A longitudinal study of four-year changes in physical fitness among university students before and after COVID-19: 2019–2022

Liangru Guo; Liang Jiang; Huizhi Huang

doi:10.1371/journal.pone.0334088

. 2025 Oct 10;20(10):e0334088. doi: 10.1371/journal.pone.0334088

A longitudinal study of four-year changes in physical fitness among university students before and after COVID-19: 2019–2022

Liangru Guo ¹, Liang Jiang ^1,^*, Huizhi Huang ¹

Editor: Mohamed Ahmed Said²

PMCID: PMC12513638 PMID: 41071790

Abstract

Background

Physical fitness is a key indicator of health in youth and was significantly affected by the COVID-19 pandemic. However, longitudinal studies tracking pandemic-related fitness changes over four years in university students, particularly those enrolled before the pandemic, remain scarce. Understanding these long-term effects on body composition, fitness, and obesity prevalence—with attention to sex differences—is essential.

Methods

This four-year cohort study included 4,413 Chinese university students (27% male, 73% female). From 2019 to 2022, participants underwent annual physical fitness assessments, measuring height, weight, vital capacity, long-jump, sit-reach, 50-m run, and sex-specific tests (1,000-m run/pull-ups for males; 800-m run/sit-ups for females). Statistical analyses included one-way ANOVA, LSD tests, and Chi-squared tests.

Results

Weight and obesity rates increased significantly, with male obesity rising from 6.97% to 11.6% and female obesity from 1.9% to 3.45%. Overweight prevalence also grew slightly. Vital capacity peaked in 2021 but declined sharply in 2022 (males: 4,114.16 mL to 3,934.31 mL; females: 3,314.69 mL to 2,957.8 mL). Long-jump and sit-reach performance declined, and cardiorespiratory endurance (1,000-m/800-m runs) worsened post-2020. Female students improved in 50-m runs and sit-ups, while males showed no significant changes in 50-m runs or pull-ups.

Conclusions

The pandemic significantly impacted university students’ physical fitness over four years, exacerbating obesity risks and declining cardiorespiratory endurance, particularly in males. Schools should prioritize BMI management, obesity prevention, and targeted fitness interventions—emphasizing agility, strength, and late-stage cardiorespiratory training—to mitigate long-term health consequences.

1 Introduction

Coronavirus Disease 2019 (COVID-19) was first identified in 2019 and subsequently spread rapidly to most countries around the world in just a few months, becoming a global public health crisis [1]. The pandemic has not only put enormous pressure on global healthcare systems, but has also had a profound impact on human physical and mental health. An international online survey study covering multiple countries showed that home quarantine measures during the COVID-19 pandemic had a significant negative impact on all physical activity (PA) intensity levels, including vigorous, moderate, walking, and overall activity. In addition, it was found that people’s daily sitting time increased significantly from an average of 5–8 hours during the pandemic, and that this increase in sedentary behavior severely impacted the public’s level of physical fitness [2].

The university years represent a critical transition period from adolescence to adulthood, during which individuals establish long-term lifestyle and behavioral patterns [3]. However, the COVID-19 pandemic and its associated restrictions disrupted this formative phase. In China, strict containment measures—including prolonged campus closures and a rapid shift to online learning (December 2019–September 2020)—fundamentally altered daily life. While effective in curbing viral transmission, these policies inadvertently reduced PA levels among university students, a population particularly vulnerable to lifestyle-related health risks. Emerging evidence links sedentary behavior during the pandemic to adverse health outcomes, including obesity, hypertension, and metabolic disorders [4–7]. Among university students, studies report significant PA declines and weight gain due to restricted mobility and reduced sports participation [8]. Given PA’s established role in preventing chronic diseases, these trends raise concerns about lasting health implications for this demographic.

Declining physical fitness has become a global social problem that has been further exacerbated, especially during the COVID-19 pandemic [9]. Several studies worldwide have focused on how the restrictions resulting from the COVID-19 pandemic exerted impacts on the physical fitness of children and adolescents, with the vast majority of findings suggesting significant negative impacts on physical fitness due to decreased PA and increased sedentary behavior [10–14]. However, recent studies have also revealed the complexity of this issue. One of these studies showed that not all health indicators were negatively affected by the lockdown, with body mass index (BMI), muscle strength, and flexibility qualities being the main ones affected [15]; another study pointed out that Chinese university students experienced an increase in BMI both during and after the lockdown [16]. These two studies are important references: the first study conducted a one-year follow-up of the effects of the COVID-19 lockdown on BMI and physical fitness of Chinese university students; the second study analyzed the changes in BMI mainly over a three-year follow-up period.

Although these studies provide valuable insights, their shorter-term designs (1–3 years) limit the ability to distinguish between transient disruptions and sustained shifts in physical fitness. A four-year longitudinal study (2019–2022) offers unique advantages by capturing: (1) pre-pandemic baseline measures (2019), essential for isolating true pandemic effects; (2) acute-phase declines during strict lockdowns (2020); (3) post-lockdown recovery or adaptation patterns (2021–2022); and (4) potential sex- or policy-specific trajectories that shorter studies may overlook. Crucially, this extended timeframe allows us to assess whether observed changes represent temporary fluctuations or sustained trends—a distinction essential not only for public health planning but also for developing targeted strategies to prevent and treat long-term health outcomes related to PA.

This longitudinal study uniquely examines four-year changes in body composition (2019–2022) among university freshmen enrolled pre-pandemic (2019 cohort). We assessed body size through standardized anthropometric measurements (height, weight and BMI), alongside physical fitness tests. Our analysis focuses on temporal patterns and sex differences in overweight/obesity prevalence and fitness parameters, providing critical evidence to guide policymakers in preventing and mitigating long-term health outcomes associated with reduced PA under pandemic containment measures among student populations.

2 Materials and methods

The study was conducted in accordance with the Declaration of Helsinki, and approved by the Institutional Review Board of the School of Sports Science, Hengyang Normal University OF INSTITUTE(September 18, 2019).

2.1 Study population

The recruitment period for this study spanned from September 5, 2019, to September 28, 2019. A total of 4,413 subjects, including 1,206 male and 3,207 female students (mean age = 17.90 years, SD = 0.90), were selected from freshmen enrolled during this period at a teacher training university in Hunan Province and were followed up for four years throughout their university study.

The study utilized a convenience sample consisting of incoming freshmen from the class of 2019 who were both available and willing to participate. Inclusion required students to provide written informed consent and complete baseline health and demographic questionnaires. Individuals with pre-existing chronic health conditions—such as cardiovascular disease or severe musculoskeletal disorders—or other physical limitations affecting exercise participation were excluded. Despite this, the sample maintained representativeness by encompassing all consenting students from the admitted cohort, thereby reducing potential selection bias.

All physical fitness tests were conducted using uniform, calibrated measuring devices to ensure the comparability of results across different testing periods. According to the “China Student Physical Fitness and Health Research Workbook” [17], the physical fitness and health data of these university students were investigated in 2019 (freshman stage, before the pandemic), 2020 (sophomore stage, during the pandemic), 2021 (junior stage, after the pandemic), and 2022 (senior stage, after the pandemic). A total of 4572 students participated in the baseline survey in 2019. Over the four-year period, 159 participants were lost to follow-up due to [briefly state reasons, e.g., voluntary withdrawal, transfer, or incomplete testing], resulting in a final analytical sample of 4413 students (1206 males and 3207 females) who completed all assessments across all four years, representing a retention rate of 96.5%. Informed consent was obtained from all participants prior to inclusion in the study.

2.2 Physical fitness test

To ensure consistency in data collection, all physical fitness tests throughout the four-year study period were administered by the same team of trained physical education professors. Prior to the study, all test administrators underwent a standardized training protocol to ensure uniform assessment procedures. Physical fitness tests for both male and female included height, weight, vital capacity, long-jump, sit-reach, and 50-m run. Sex-specific tests were included to account for physiological differences: pull-ups and a 1,000-m run for male assess upper-body strength and endurance, while sit-ups and an 800-m run for female measure core strength and aerobic capacity. To ensure measurement consistency, all subjective assessments were conducted following unified training, with standardized scoring criteria strictly enforced among all testers. Physical fitness tests were administered by physical education professors and conducted annually from October through November. All tests were performed under consistent conditions, including indoor venues with standardized equipment (temperature maintained at 20–24°C and relative humidity at 40–60%), and scheduled at the same time of day (morning sessions) to minimize environmental variability. Potential variations were documented and accounted for in the statistical analysis. Before each fitness test, participants completed a standardized 15-minute warm-up routine consisting of light jogging (5 minutes), dynamic stretching (5 minutes for major muscle groups), and sport-specific activation exercises (5 minutes). To maintain adherence to protocols, test administrators received annual training, and participant engagement was monitored through attendance records and real-time supervision during testing.

2.2.1 Vital capacity.

The vital capacity was measured using an air spirometer (GMCS-IV; Jianmin, Beijing, China) with a dry and sterilized plastic mouthpiece. Participants took a deep breath and slowly exhaled into the mouthpiece until they could no longer exhale. The air spirometer automatically calculated the maximum air volume (vital capacity per milliliter) and displayed the result upon completion of the exhalation maneuver. Participants performed the test twice with a 15-second interval between trials, and the higher of the two values, as determined by the standardized scoring protocol, was recorded.

2.2.2 Long-jump.

Participants were asked to stand behind the starting line with their feet apart and jump forward in a natural position. Participants were also instructed that both feet should jump at the same time from a standing position and that no additional movements should be made. Horizontal distance was measured from the trailing edge of the starting point to the trailing edge of the nearest landing point. Each student was allowed for three attempts. The longest jump was recorded in centimeters.

2.2.3 Sit-reach.

Participants were tested for sitting and stretching using a seated stretch box device, in a seated position and keeping their legs straight. The participant’s upper body was leaned forward, with his/her arms straightened forward and his/her feet separated by 10–15 centimeters while pushing horizontally forward against the test board (GMCS-IV; Jianmin, Beijing, China). The participant’s fingertips extended and gradually pushed the test bar forward until he/she was unable to push further. Each student was given two attempts. The farthest distance was recorded in centimeters.

2.2.4 Pull-ups.

The test is aimed to check a participant’s upper body strength. The participant held the bar in a shoulder-width hand to form a straight-arm suspension position, and then pulled the entire weight upward simultaneously using only the arms while keeping the body and arms straight. In addition, the participant’s body could not make additional movements, such as swinging or oscillating. In order to complete a pull-up, the participants were required to pull themselves up until their chins cleared the horizontal level of the bar. The final number of correctly completed pull-ups was recorded. No strict time limit was imposed; participants performed pull-ups continuously until exhaustion.

2.2.5 Running tests (50-m, 800-m, and 1,000-m Runs).

50-m Run: Participants began in a standing position at the starting line of a 50-meter straight track. Upon the physical education professor’s verbal signal (“ready-and-go”), the timekeeper started recording. Time stopped when the participant’s chest crossed the finish line. The recorded time (in seconds, to one decimal place) was rounded up if the second decimal digit was non-zero. Each participant completed two trials, with the better performance was recorded.

800-m Run: Female students performed an 800-meter run, starting behind the line upon the physical education professor’s “ready-and-go” command. Time (in minutes:seconds, to one decimal place) was recorded upon chest crossing the finish line, with the recorded time rounded to the nearest tenth of a second. Only one attempt was allowed.

1,000-m Run: Male students completed a 1,000-meter run under identical protocols to the 800-m and 50-m runs regarding starting procedure, timing method, and rounding rule (single attempt, recorded time rounded to the nearest tenth of a second).

2.2.7 Body mass index (BMI).

BMI was used to measure the degree of overweight and obesity of the participants, expressed as weight (kg)/height (m)². The WHO-defined BMI criteria were used, with a BMI ≥ 28 (kg/m²) defined as obesity and 24 ≤ BMI < 27.9 defined as overweight. Participants’ height and weight were measured by using electronic weight and height scales. Participants were instructed to remove their shoes and wear light indoor clothing before standing upright on the electronic scale. The scale then automatically measured weight and height to the nearest 0.1 cm.

2.3 Statistical analysis

Data were initially entered using Excel 2016 and statistically analyzed using the software SPSS 27.0; quantitative data were expressed using mean ± standard deviation. Given the repeated measurements across multiple years, one-way analysis of variance (ANOVA) was selected to compare adjacent years stratified by sex, as it provides a straightforward method for detecting interannual differences while accounting for within-group variability. Potential confounding variables such as age, baseline fitness, and socioeconomic status were not explicitly adjusted for in the analysis. The χ² test in SPSS 27.0 was used to analyze differences in the detection rates of overweight and obesity in the same year for different sex groups; and χ² linear trend test was used to analyze the trends in the detection rates of overweight and obesity in the whole population, both sex, for the years 2019–2022. The annual growth rate (%/year) of the detection rate of each sex-age group in different periods was calculated (or folded): Annual growth rate = (detection rate in a certain year – detection rate in the previous year)/ (a certain year – the previous year) × 100%. To ensure measurement consistency, all physical fitness testing procedures were standardized, and trained personnel conducted the assessments using calibrated equipment. A two-sided test was used, and a difference of P < 0.05 was considered statistically significant. In this study, data distribution was visualized using box plots (also known as box-and-whisker plots), which display the minimum, lower quartile (Q1), median (Q2), upper quartile (Q3), and maximum values. The box plots were generated using Microsoft Excel.

3 Results

3.1 Demographic characteristics of participants

Table 1 summarizes the demographic characteristics of the participants: female students outnumbered male students (72.7% to 27.3%); their age was calculated based on the enrollment in September 2019, with the 17 ≤ YEAR ≤ 19 year old age group accounting for 91.9% of the total participants, followed by the < 17 year old age group accounting for 4.7% and the > 19 year old age group accounting for 3.4%; 89.2% of the university students were Han Chinese and 10.8% were ethnic minorities.

Table 1. Demographic characteristics.

Variable	Category	Frequency	Percent valid	Effective percentage	Cumulative percentage
Sex	Male	1,206	27.3	27.3	27.3
Sex	Female	3,207	72.7	72.7	100.0
Age	<17	208	4.7	4.7	4.7
	17 ≤ year≤19	4,055	91.9	91.9	96.6
	>19	150	3.4	3.4	100.0
Ethnicity	Han Chinese	3,935	89.2	89.2	89.2
Ethnicity	Ethnic minority	478	10.8	10.8	100.0

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3.2. Results of ANOVA for university students’ physical fitness

3.2.1 Changes in body shape.

In terms of height changes, the male group did not show a significant difference in the mean height between the four years (F = 1.745, p > 0.05). In contrast, the female group showed a significant difference in the mean height (F = 7.375, p < 0.01). The LSD test, a post-hoc test, showed that the difference in the height of the females was not significant between 2019 and 2020, nor between 2021 and 2022, but those in the latter two years (2021–2022) were significantly higher than those in the first two years (2019–2020) (Table 2).

Table 2. Results of ANOVA.

Variable	Sex	N	2019	2020	2021	2022	F	LSD
Height	Male	1206	172.50 (6.15)	172.50 (6.15)	172.93 (6.23)	172.89 (6.20)	1.75
Height	Female	3207	160.15 (5.48)	160.15 (5.48)	160.56 (5.62)	160.64 (5.51)	7.36**	1&2 < 3&4
Weight	Male	1206	65.75 (12.33)	65.75 (12.33)	66.91 (12.68)	69.16 (12.95)	19.70**	1&2 < 3 < 4
Weight	Female	3207	53.96 (7.54)	53.92 (7.74)	53.96 (7.94)	54.90 (8.73)	11.45**	1&2&3 < 4
BMI	Male	1206	22.06 (3.75)	21.07 (2.67)	20.94 (2.79)	21.22 (3.01)	20.10**	1&2&3 < 4
BMI	Female	3207	21.38 (3.17)	21.00 (2.68)	21.97 (3.57)	21.26 (3.10)	8.27**	1&2&3 < 4
Vital capacity	Male	1206	3880.37 (475.95)	3778.78 (459.56)	4114.16 (446.12)	3934.31 (283.98)	132.75**	2 < 1 < 4 < 3
Vital capacity	Female	3207	2939.28 (337.19)	2941.09 (336.51)	3314.69 (343.61)	2957.80 (344.47)	941.84**	1&2 < 4 < 3
50-m run	Male	1206	7.16 (0.48)	7.16 (0.48)	7.18 (0.46)	7.18 (0.47)	0.69
50-m run	Female	3207	9.39 (0.42)	9.39 (0.42)	9.38 (0.42)	8.91 (0.31)	1,187.22**	4 < 1&2&3
Long-jump	Male	1206	228.94 (14.68)	218.18 (18.54)	229.19 (18.94)	221.75 (14.17)	128.24**	2 < 4 < 3&1
Long-jump	Female	3207	161.80 (13.33)	163.06 (12.59)	176.55 (13.70)	161.21 (13.00)	988.04**	1&4 < 2 < 3
Sit-reach	Male	1206	16.07 (6.44)	16.07 (6.44)	15.49 (7.34)	14.7 (6.85)	11.03**	4 < 3 < 1&2
Sit-reach	Female	3207	19.63 (6.00)	19.63 (6.00)	18.5 (6.30)	16.89 (6.08)	144.36**	4 < 3 < 1&2
1,000-m-run	Male	1206	236.83 (23.54)	236.83 (23.54)	253.19 (17.57)	252.92 (17.46)	246.01**	1&2 < 3&4
800-m-run	Female	3207	251.69 (17.85)	251.69 (17.85)	253.6 (17.10)	253.36 (17.35)	11.16**	1&2 < 3&4
Pull-ups	Male	1206	12.16 (3.53)	12.16 (3.53)	12.23 (3.48)	12.24 (3.35)	0.17
1-min-sit-ups	Female	3207	35.06 (5.66)	35.21 (5.60)	39.54 (5.78)	41.1 (5.88)	912.35**	1&2 < 3 < 4

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Note: **P < 0.01; 1 = 2019; 2 = 2020; 3 = 2021; 4 = 2022. Body mass index (BMI)

Regarding weight changes, there was a significant difference in the mean weight of the male group (F = 19.698, p < 0.01). LSD analysis showed that there was no significant difference in weight between 2019 and 2020, but there was a trend of increasing year by year from 2021 to 2022. A significant difference was also observed in females (F = 11.446, p < 0.01). Their weight remained stable between 2019 and 2021 but increased significantly in 2022 compared to the preceding three years (Table 2).

In terms of BMI, there was a significant difference in the males (F = 20.095, p < 0.01), whose BMI remained stable between 2019–2021 and was significantly higher in 2022. A similar trend was observed in the females (F = 8.269, p < 0.01), whose BMI did not change significantly between 2019, 2020 and 2021 and was significantly higher in 2022 than those in the previous three years. (Table 2)

3.2.2 Changes in physical fitness.

Significant differences were observed across years in the vital capacity test for both males (F = 132.75, p < 0.01) and females (F = 941.83, p < 0.01). In males, vital capacity increased from 2019 to 2021, peaked in 2021, and then declined in 2022. Females showed lower values during 2019–2020 compared to 2022, with both periods being significantly lower than the peak in 2021.

In the 50-m run test, no significant difference was found in males (F = 0.69, p > 0.05), whereas a significant difference was observed in females (F = 1,187.2, p < 0.01), with performance remaining stable during 2019–2021 and improving significantly in 2022.

Both the long-jump and sit-reach tests revealed similar trends across sexes. In the long-jump, significant differences were detected in males (F = 128.238, p < 0.01) and females (F = 988.04, p < 0.01). Male scores were lower in 2020 than in 2022, and both were lower than in 2019 and 2021, with no difference between the latter two years. Female scores were significantly lower in 2019 and 2022 than in 2020, and all three years were lower than 2021, with no difference between 2019 and 2022. For the sit-reach test, both males (F = 11.032, p < 0.01) and females (F = 144.36, p < 0.01) exhibited a decreasing trend over time, with no significant difference between 2019 and 2020 in either group.

Similarly, the endurance running test (1,000-m for males, F = 246.005, p < 0.01; 800-m for females, F = 11.161, p < 0.01) showed comparable patterns: performance was significantly better in 2019 and 2020 than in 2021 and 2022, with no significant differences within the earlier or later pairs of years.

Additionally, a significant difference was found in the 1-min sit-ups test for females (F = 912.35, p < 0.01), with scores in 2019 and 2020 being lower than in 2021, and all three years lower than 2022, and no difference between 2019 and 2020. (Table 2)

3.3 Detection of overweight and obesity among university students

3.3.1 Detection of obesity.

In the longitudinal study on the university students’ obesity detection rates, an increasing trend year by year was observed. The obesity detection rate for the males increased from 6.97% in 2019 to 11.6% in 2022, showing a linear increase over time [χ² (trend)=18.44, P < 0.001)]. The obesity detection rate for the females increased from 1.9% in 2019 to 3.45% in 2022, with a linear increase over time [χ² (trend)=19.81, P < 0.001)]. The figure for the whole population increased from 3.29% to 5.69%, indicating a linear trend over time [χ² (trend)=37.39, P < 0.001]. The boxplot analysis revealed a progressive increase in BMI values across the study period (2019–2022) for both sex, with a clear upward trend observed year by year (Figs 1 and 2). Sex-stratified χ² tests revealed significantly higher obesity rates in males versus females annually (P < 0.01). Notably, 2020 (first COVID-19 year) showed no significant obesity rate increase for either sex (Table 3).

Table 3. Comparison of obesity detection rates.

Groups	2019			2020			2021			2022			χ²(trend)
Groups	Statistical value	Total number of people	Number of detections (detection rate)	Statistical value	Total number of people	Number of detections (detection rate)	Statistical value	Total number of people	Number of detections (detection rate)	Statistical value	Total number of people	Number of detections (detection rate)
Male		1206	84 (6.97%)		1206	84 (5.97%)		1206	102 (8.46%)		1206	140 (11.6%)	18.440**
Female		3207	61 (1.90%)		3207	60 (1.87%)		3207	85 (2.65%)		3207	111 (3.46%)	19.810**
	χ²	70.7**		χ²	72.05**		χ²	72.84**		χ²	108.46**
the total		4413	145 (3.29%)		4413	144 (3.26%)		4413	187 (4.24%)		4413	251 (5.69%)	37.39**

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Note: **P < 0.01.

Annual obesity rate growth rates demonstrated sex-specific patterns: males (−1.00%, 2.49%, 3.14%) and females (−0.03%, 0.78%, 0.81%) between adjacent years. Both sexes showed slight declines in 2019–2020 followed by steady increases in 2020–2022, with males exhibiting consistently higher growth rates.

3.3.2 Detection of overweight.

In the longitudinal study on the university students’ overweight detection rates, the overweight detection rate of the male university students increased from 19.98% in 2019 to 20.9% in 2022, and that of the female university students increased from 10.98% in 2019 to 11.85% in 2022. The figure for the entire population increased from 13.43% to 14.32%. In terms of sex stratification, the results of χ² test showed that the difference in overweight detection rates between male and female university students each year was statistically significant (P < 0.01), with the males having a higher overweight detection rate than the females. It is worth noting that there was no significant increase in the overweight detection rate in the male and female groups from 2020, which was the first year of the COVID-19 pandemic. The overweight detection rate showed a significant decrease in 2021 and a significant increase in 2022 (Table 4).

Table 4. Comparison of overweight detection rates.

Groups	2019			2020				2021			2022		χ²(trend)
	Statistical value	Total number of people	Number of detections (detection rate)	Statistical value	Total number of people	Number of detections (detection rate)	Statistical value	Total number of people	Number of detections (detection rate)	Statistical value	Total number of people	Number of detections (detection rate)
Male		1206	241 (19.98%)		1206	241 (19.8%)		1206	216 (17.91%)		1206	252 (20.9%)	0.897
Female		3207	352 (10.98%)		3207	334 (10.41%)		3207	299 (9.32%)		3207	380 (11.85%)	0.537
	χ²	61.131**			χ²	120.793**	χ²	62.694**		χ²	58.454**
the total		4413	593 (13.43%)		4413	575 (13.03%)		4413	515 (11.67%)		4413	632 (14.32%)	0.57

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Note: **P < 0.01

Between 2019 and 2022, the annual growth rates of the overweight detection rate among the males were −0.18%, −1.89%, and 2.99% between adjacent years, respectively, and the figures for the females were −0.57%, −1.09%, and 2.53% between adjacent years, respectively. The annual growth rates of the overweight detection rate of both the males and the females showed a decreasing trend from 2019 to 2021, and continued to increase from 2021 to 2022, with the annual growth rate of the males being much higher than that of the females.

4 Discussions

This longitudinal study provides the first evidence of COVID-19’s impact on physical fitness trends among Chinese university students over four years (2019–2022). Key findings revealed sex-specific changes: females showed significant temporal differences in height, weight, and BMI, while males exhibited changes only in weight and BMI. Physical function (e.g., vital capacity) and fitness metrics (e.g., long jump, sit-reach) declined significantly in both sexes, with females also showing reductions in 50-m run and sit-up performance. Notably, obesity rates increased annually, particularly during the 2020 pandemic peak, with males consistently demonstrating higher overweight/obesity rates than females. Overweight rates initially declined (2019–2021) but rebounded in 2022.

4.1 Changes in the body size of college students

The results on changes in the body size have similarities with the findings of a number of international studies that have documented the negative impact of the COVID-19 pandemic on the body size. Numerous studies similarly found an increase in BMI and a decrease in physical fitness among university students following the COVID-19 lockdown due to prolonged social distancing and school closures [18,19]. In our analysis, these disruptions—including lockdowns limiting outdoor activity and online learning reducing structured physical education—were explicitly considered as key contextual factors explaining the 2020 obesity surge. Although the COVID-19 pandemic appeared to be receding in 2022, the obesity and metabolic dysregulation pandemic continues to rage [20]. These trends are consistent with the fact that weight, BMI, and obesity rates among the studied population of university students showed a significant yearly increasing trend over time. In addition, the present study also found that, between sexes, the detection rates of overweight and obesity were much greater among the male students than among the female students during the four years of university, a finding that is also consistent with the findings of most previous studies [16,21,22]. This phenomenon may be related to the fact that females are more body-conscious and therefore less likely to gain weight during the pandemic than males [16].

However, it is worth noting that a previous study noted a significant increase in adolescent obesity detection rates in 2020 compared to 2019, with a decreasing trend in 2021 and 2022 [23]. The reason for this discrepancy may be related to the age range of the sample size. The respondents of this study were university students with an average age of 18–20 years. The lack of teacher supervision and insufficient self-discipline may have led to an increase in the obesity detection rate year after year. Previous studies have focused on the adolescent population aged 6–14 years, and their conclusions may differ from those from the university students. In addition, the results of this study showed that the overweight detection rate among the university students showed a decreasing trend from 2019 to 2021 and was significantly higher in 2022 than in the previous three years. This finding differs from the results of a previous study that found an increasing trend in overweight detection rates among university students from 2019 to 2021 [24]. This difference may be related to sample selection. The previous study focused on data from 10 universities in Hunan Province, whereas this study selected only one teacher training university in Hunan Province, where the female to male ratio was approximately 3:1. This substantial difference in the gender composition of the sample may be one of the reasons for the inconsistent results. Compared to pre-pandemic university populations without COVID-19 influence, our cohort exhibited intensified overweight/obesity trends, particularly in males. This acceleration suggests pandemic-specific impacts (e.g., prolonged campus lockdowns, reduced PA opportunities) exacerbated existing risk factors. However, the female-majority sample may have moderated overall trends, as females generally maintained lower obesity rates despite similar environmental pressures.

4.2 Changes in the physical fitness of university students

Regarding the results of changes in physical fitness, this study fully discussed from three perspectives: cardiorespiratory fitness, muscular strength and flexibility. From the perspective of cardiorespiratory fitness, the scores of both sex from the 1,000-m run (male) and 800-m run (female) were significantly better in 2019 and 2020 than in 2021 and 2022. This change may be related to the characteristics of China’s education system. In China’s higher education system, freshmen and sophomores are required to complete a certain number of physical education credits, whereas juniors and seniors are no longer subjected to a mandatory requirement for physical education [25]. In addition, PA and physical fitness (PF) levels of university students decline with age, with PF increasing from first to second year but gradually slowing from third to fourth year [26]. This finding is consistent with the results of a previous study, which noted a decreasing trend in endurance quality among university students one year after the implementation of COVID-19 restrictions (2020) [27,28]. From the perspective of muscular strength, the results of this study showed that the male students’ performance in the 50-m run and pull-ups did not change significantly over the four-year period, suggesting that male students’ explosive and upper body strength remained stable during the COVID-19 pandemic. In contrast, the female students’ performance in the 50-m run was significantly better in 2022 than in the previous three years, and their performance in 1-min sit-ups showed a year-to-year increase. These sex-specific improvements, particularly among females, may be partially attributed to social norms and increased familiarity with structured exercise in a university setting. As previous research in both civilian and military contexts has suggested, women often exhibit substantial gains in physical performance when provided with equal opportunities for training, potentially due to a lower initial baseline and thus greater room for improvement [29]. In addition, long-jump scores were significantly lower in freshmen and seniors than in sophomores and juniors. These results suggest that muscle strength did not significantly decrease in both the males and the females as a result of COVID-19. This phenomenon may be attributed to the fact that during home quarantine at the beginning of the pandemic, the university’s physical education program required students to perform daily resistance training, including coursework such as push-ups, sit-ups, and weighted squats. Although the course was conducted online, it was still supervised online by a teacher. In addition, in China’s higher education system, coursework accounts for 20% of the score for physical education classes and counts toward a student’s grade point average (GPA) [25]. This system may have motivated students to maintain a certain amount of exercise during the pandemic, thus maintaining muscle strength levels. From the perspective of flexibility, this study found a decreasing trend in flexibility indicators over time for both the male and female students. This result is consistent with previous studies suggesting that home quarantine during a pandemic led to a decrease in flexibility among university students [15,30]. For example, a study identified the lack of systematic stretching training during the pandemic as a major cause of decreased flexibility [31]. In addition, the limited range of daily activities during home quarantine may have led to decreased joint mobility and muscle stretching, especially the iliopsoas muscle tightness of students due to prolonged sedentary periods resulting from online courses [32]. These changes highlight the long-term risk of reduced PA during pandemic disruptions, as flexibility declines may persist even after lockdowns end, potentially increasing injury risk and impairing overall mobility.

4.3 Practical implications

The findings of this study have important practical implications for public health and health promotion. The findings emphasize the importance of maintaining a healthy lifestyle during a pandemic, especially in terms of diet and PA. Second, the findings suggest the need for educational institutions and public health authorities to develop targeted interventions to address the growing of obesity in the university students. Finally, this study provides a scientific basis for future health policy development, especially on how to balance pandemic prevention and control with health promotion.

4.4 Limitations and future research directions

This study is subject to some limitations, although it study provides valuable data on the impact of the COVID-19 pandemic on the physical fitness of university students. First, the samples of this study were university students in a certain region of China, which may not fully represent the overall situation of university students nationwide. Second,while our longitudinal design spanned four years, missing data due to student attrition or incomplete testing records may affect result robustness. Additionally, the study data mainly relied on school physical examination data, which may have some measurement errors. Moreover, potential confounding variables such as age, baseline fitness, and socioeconomic status were not explicitly adjusted for in the analysis, which could potentially influence the outcomes and their interpretation. Furthermore, due to the large number of test items and participants, multiple data collectors were involved throughout the study period. Despite efforts to standardize protocols, this may have introduced inter-rater variability. Finally, the significant gender disproportion in the study population (with females being overrepresented) may have introduced bias and skewed the results, necessitating caution in the interpretation of the findings.

Based on the limitations of this study, future research can be conducted in the following ways: first, expand the sample size to cover more regions and different types of colleges and universities, so as to improve the representativeness and generalizability of the study. Second, more accurate measurement tools, such as accelerometers and body composition analyzers, can be used to reduce measurement errors. Finally, future studies could further explore the relationship between mental health and physical fitness during the pandemic, especially the effects of psychological factors such as anxiety and depression on body weight and physical fitness.

5 Conclusions

This study finds that COVID-19 significantly impacted the physical fitness and health of 2019-enrolled university students: obesity rates (especially among males) rose annually; flexibility declined consistently; endurance remained stable in the first two years but dropped in junior and senior years; and strength was unaffected. We recommend targeted interventions to control BMI (with focus on males), enhance agility, explosiveness, and muscular strength across all stages, and prioritize cardiorespiratory endurance improvement in the third and fourth years. These findings offer insights for exploring school closure/online learning effects on youth fitness and support policy-making for adolescent health. Limitations include a single cohort focus, and future research could expand to multi-cohort or longitudinal analyses to generalize conclusions.

Supporting information

S1 File. Supplementary material.

(DOCX)

pone.0334088.s001.docx^{(99.8KB, docx)}

Data Availability

All relevant data are within the paper and its Supporting Information files.

Funding Statement

(1)The Research Project on Teaching Reform of General Colleges and Universities in Hunan Province in 2023 (Project No. HNJG-20230872) Recipient: Liangru Guo (2)The Fourteenth Five-Year Plan of Educational Science in Hunan Province in 2024 (Project No. XJK24CTW013) Recipient: Liangru Guo (3)The Deepening Educational Evaluation Reform in the New Era in Hunan Province in 2022 Pilot Project (Project No. TGYX202207). Conceptualization, L.R.G. and L.J.; validation., L.R.G. and L.J.; formal analysis, L.R.G.; investigation, L.J.; resources, L.J.; writing—original draft preparation, L.R.G.; writing—review and editing, L.J.; supervision, L.J.; project administration, L.J.; funding acquisition, L.R.G and L.J. All authors have read and agreed to the published version of the manuscript.

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PLoS One. doi: 10.1371/journal.pone.0334088.r001

Decision Letter 0

Mohamed Ahmed Said

26 Jul 2025

PONE-D-25-29142A longitudinal study of four-year changes in physical fitness among university students before and after COVID-19: 2019-2022PLOS ONE

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Reviewer #1: General Assessment:

The manuscript presents original research that investigates changes in body composition and physical fitness among Chinese university students over a four-year period spanning before, during, and after the COVID-19 pandemic. The topic is of public health relevance, and the authors have collected a large dataset with multiple fitness indicators. Overall, the study meets the journal’s criteria for technical rigor and ethical compliance. However, several aspects require minor revisions to improve the clarity, consistency, and presentation of the work.

1. Scientific Rigor and Methods:

The cohort design is appropriate for the research objectives, and the repeated physical fitness testing across four years is a strength.

The statistical approach is acceptable for basic trend analysis. Nevertheless, the rationale for selecting ANOVA over more robust longitudinal models could be briefly explained. Additionally, more detail on data collection quality control (e.g., measurement consistency) is encouraged.

2. Tables and Figures:

Tables 2, 3, and 4 require formatting adjustments for clarity. Some rows and columns are misaligned, and headers are difficult to follow. Similarly, Figures 1 and 2 do not effectively communicate the temporal changes in BMI. Consider replacing the 3D scatterplots with simpler and more interpretable line charts or boxplots.

3. Discussion Section:

The manuscript lacks a focused discussion section. Beyond reporting results, the paper should include critical interpretation, explanations for observed trends, comparison with existing studies, and acknowledgment of limitations. A structured discussion would greatly improve the manuscript’s clarity and depth.

4. Writing and Organization:

The manuscript is generally well written in standard English. Minor language polishing could improve clarity and readability. The structure would benefit from clearer section transitions and concise topic sentences in the results and discussion.

5. Ethics and Data Availability:

Ethical approval and informed consent are clearly stated.

Data availability is appropriately addressed and aligns with PLOS ONE standards.

Recommendation:

The study is scientifically sound and methodologically appropriate. With minor revisions focused on improving table formatting, figure clarity, and manuscript organization, it will be suitable for publication.

Reviewer #2: Dear Authors,

Congratulations on your choice of topic. I read the article with interest. The manuscript provides important information on the physical fitness of students in the context of the COVID-19 pandemic. The study is based on measurements of physical fitness (tests), body weight and height, and spirometry. The description lacks information on whether the researchers conducting the study had been trained beforehand. The paper also does not indicate whether the study was conducted using uniform, calibrated measuring devices, which seems important from the point of view of the comparability of the results. The study has its limitations, but the authors have drawn attention to them by describing them in the limitations section. In their recommendations for the future, they suggest, among other things, the use of objective tools, such as accelerometers, which will allow for a more precise and reliable assessment of physical activity levels.

The study focuses on a large group of students from Hunan Province, but it should be noted that this group is not representative of the entire student population. Although this sample structure provides valuable data, it may not fully reflect the specific cultural conditions and barriers characteristic of this group. The authors recognise this and draw attention to it when discussing the limitations of the study.

Detailed suggestions are included in the comments on the article.

Reviewer #3: A longitudinal study of four-year changes in physical fitness among university students before and after COVID-19: 2019-2022

General Comments

Thank you for the opportunity to review this article, and I would like to congratulate the authors on their efforts in compiling this work.

The study presents original research, a longitudinal analysis of physical fitness changes in Chinese university students before and after the COVID-19 pandemic (2019-2022). The research focus and dataset are novel, and the manuscript explicitly addresses a gap in the literature regarding long-term impacts of the pandemic on university students.

However, the manuscript would benefit from further adjustments and revisions as proposed herein, section by section.

Title and Short Title

• The titles are clear and accurately reflect the study's content.

• I suggest you ensure consistency in the use of "pre/post-COVID-19" versus "before and after COVID-19" if used in other materials (e.g., in databases or indexing).

Abstract

• As it is, the abstract is too long. The number of words is almost double the recommended standard by PLOS ONE. Consider slightly rephrasing some sentences for tighter prose and conciseness, typical for abstracts where every word counts.

• Be attentive to the use of capitalization; for instance, in line 28, the letter 'V' in the word "vital" should be capitalized. Review the entire document for any similar inconsistencies.

• Consider providing keywords at the end of the abstract to improve indexing and discoverability in academic databases and search engines.

Introduction

• While the literature review effectively identifies the research gap, consider briefly strengthening the rationale for why a four-year longitudinal study from 2019 (pre-pandemic) to 2022 (post-pandemic) is especially valuable compared to existing shorter-term studies. What specific insights does this longer timeframe offer that others do not?

• Where some words have been defined in the first appearance and an abbreviation provided, the use of the abbreviation in the succeeding sections is best practice, e.g., physical activity (PA). Use PA in the succeeding paragraphs—see lines 66, 69, 79… Scan through the entire manuscript and use the abbreviations where applicable.

• Revise the use of tense in line 65.

• Is this study grounded on any theory that support its scientific constructs?

Materials and Methods

While the methods are generally described, more details should be provided for full reproducibility. Consider addressing the following:

• How were the participants selected, and what criteria were used to ensure a representative sample? Were there any inclusion or exclusion criteria (e.g., pre-existing health conditions, baseline fitness levels)?

• Did the physical education professors receive any specific training to ensure uniform test administration? Were the same professors involved across the four years?

• Detail in brief the specific warm-up routines in line 118.

• Were inter-rater reliability checks performed for any of the subjective measurements, for example, the form for sit-ups, long jump, or sit-reach?

• Were there any potential variations in the testing environment (e.g., indoor vs. outdoor, time of day, equipment type) across the four years that could influence results? If so, how were these controlled or accounted for in the analysis or discussion?

• How was consistent participant engagement and adherence to test protocols ensured over the four years of data collection?

• In line 170, I am not sure the correct symbol for interpretation has been used. Should this remain as 24 ≤ BMI < 27.9 or ≥ 24 BMI < 27.9? The former would mean even a BMI of 20 kg/m² was still ranked as overweight.

• How was missing data handled, especially for students who dropped out or missed annual tests? Could you report the retention rate and analyze differences between completers and dropouts to address potential attrition bias?

• Important—Provide more details on the specifications (type, model number, etc.), calibration, and validation of the equipment used for physical fitness screening for physical fitness tests to ensure measurement accuracy.

• Provide a brief justification for the use of gender-specific fitness tests (e.g., pull-ups for males and sit-ups for females) and explain the rationale behind these choices.

• Clarify whether adjustments were made for potential confounding variables (e.g., age, baseline fitness, socioeconomic status) in the statistical analysis.

Results

Generally, the results section is comprehensive and well-structured, with clear presentation of longitudinal trends and gender differences. The use of visualizations (e.g., 3D scatterplots) is commendable. However, the following needs improvement:

• In line 194, is the 7 ≤ YEAR ≤ 19-year-old age group accurate, or did you imply 17 instead of 7? Clarify

• Within table 1, the use of the symbol is not clear to me. Should it be presented as 17≤year≤19 or 17≥year≤19? The use of less than and greater than symbols is confusing the interpretation and understanding of this age group. Please clarify.

• In line 211, does the phrase “The same significant difference” imply similarly or that the mean weight of the female group equalled that of the male group?

• The authors need to adjust the font used in tables 1-4 to ensure proper alignment of text and values. As it is, they are juggled, making readability difficult.

• All the tables require proper formatting by improving row and column alignment to enhance readability. Tables 3 and 4 are very difficult to follow.

• Define abbreviations as a footnote where applicable in the tables, e.g., BMI.

Discussion

• Discuss how pandemic-related disruptions (e.g., lockdowns, online learning) were accounted for in the analysis and whether any adjustments were made for reduced physical activity during these periods.

• Consider discussing the potential long-term implications of the observed physical fitness changes on health outcomes, such as risk for chronic diseases or mental health issues.

• Discuss the practical significance of statistically significant findings, especially for small changes in physical fitness indicators.

• Please make sure all abbreviations are presented in full in the first appearance in the manuscript, e.g., physical fitness has been mentioned from line 53 but only abbreviated from line 396.

• Consider adding a section on the strengths of the study before the limitations section.

• In the limitations part, consider also addressing potential biases inherent in a longitudinal study, such as selection bias due to dropouts or measurement bias if test administrators changed over time.

Conclusions

• The conclusions should be provided after the discussion section.

• The conclusions are presented appropriately and directly stem from the study's findings. If possible, consider summarizing the main limitations and future research directions in the conclusion to provide a balanced perspective.

Presentation and Language

• There are some minor grammatical awkwardness and phrasings that could be improved for clarity and conciseness, e.g., line 331 “the study was aimed to” instead of “the study aimed to.” Scan the entire manuscript keenly for these kinds of errors.

• Proofread the entire manuscript thoroughly for minor spelling mistakes, e.g., recoded in line 155 instead of recorded.

• Ensure proper spacing where necessary, e.g., in line 185, space between the word rate, the equals sign, and the bracket.

• Some sentences are complex and could be simplified for broader accessibility.

Data Availability Statement

• This statement should be provided after the discussion section.

• You state, "All relevant data are within the manuscript and its supporting information files." While this is generally acceptable, PLOS ONE strongly encourages data deposition in publicly accessible repositories. If possible, consider depositing your raw data in a recognized repository and providing the accession/version number in this section. If the data cannot be made fully public (e.g., due to privacy concerns), please provide a clear statement on how other researchers can request access to the data, including contact information or a data access committee.

Ethics Statement

• As stated in lines 111 and 112, can the authors clarify why oral consent was used instead of written consent? Yet in the provided ethical approval, in the section on review of content, number 1, the board expressly states the following: “All participants will be required to sign an informed consent form, clearly understanding the purpose of the study, data collection methods, potential risks, and safeguards.”

References

• Ensure uniform in-text citations. There is a mix-up in some paragraphs. Refer to lines 354 and 358 against other paragraphs in the document and harmonize as necessary.

• Are you able to provide DOIs (Digital Object Identifiers) assigned to the cited journal papers where available? This ensures reliability and accuracy in citations.

• For online references, provide the date of accession and the link to the document.

Reporting Guidelines

• The study aligns with the STROBE guidelines for observational studies, covering all key elements such as study design, methodology, results, and ethical considerations.

Supplementary materials

• The tables are not labelled as per PLOS ONE guidelines. Label them properly as per the journal guidelines.

• The subtitles in the one-way ANOVA (female) table should be all in English for easier understanding by the global audience.

• Define abbreviations as a footnote where applicable in the tables, e.g., LSD.

• Format the lines of the tables for uniformity and decency.

Reviewer #4: The authors introduce a topic of interest to the international community on the trend of physical fitness and body weight throughout the COVID-19 pandemic in what is considered an active young adult population of university students.

The main concern of the manuscript is the missingness of data is not discussed. A study population of ~ 4,400 is described however data is only presented for ~10% of this population (~450) in the Results section without a proper discussion of loss of data/missingness in the Results or Discussion section. Secondly, the manuscript is exceedingly long, specifically the Results and Discussion sections and could use a major revision to streamline outcomes reported and interplay with current literature and findings in the Discussion. Please consider the suggested edits/comments detailed below in your revision:

SPECIFIC RECOMMENDATIONS:

1- Suggest the start of a new paragraph with introduction of college lifestyle discussion [Ln 53].

2- Suggest condensing lines 56-71 with focus on the impact of COVID-19 on PA with reference to defined declines in the university population (or weight gain if PA data not specifically available for citation) .

3- More clearly define the study population referenced in Line 86-87. How does this population compare or contrast to the current study population? Did the 3-year follow up occur post-university environment?

4- Lines 91-98 present similar context, consider merging.

5- Define body shape and how assessment will occur (Ln 93).

6- When defining the study population an age range/mean ± SD would be helpful (Ln 104) and ensure the proper word selection (e.g., boys/girls vs. men/women vs. male/female used interchangeably throughout) is appropriately used throughout.

7- Under Methods section 2.2 please define the testing conditions. Was testing in the morning, environmental conditions, were groups held consistent to ensure competitive nature of participants were controlled for throughout the separate sessions? Were they similar across the 4 year testing period? Same test providers/raters?

8- Can you clarify if a time allotment was given for the pull-ups in Section 2.2.4?

9- Consider combining Sections 2.2.5 and 2.2.6 since testing procedures were similar across both running sessions. Also, add the 800-m testing for women (Not currently mentioned).

10- Were study participants limited to specific clothing during body weight assessment across the four timepoints? Consider adding this content to Line 172.

11- Were sex differences assessed for? Please elaborate why/why not? Would be of interest to the reader and all data appears available for analysis.

12- Typo Line 194, believe it should read “17≤YEAR≤19”

13- Why is the n so low in Table 2? Did you have missing data? If so, appears significant and needs to be discussed in Section 2.3 Statistical analysis section. Appears as if only 10% of total population data is presented in Table 2 & discussed.

14- Define outcomes as sex or gender? Male/Female is considered sex, however gender is used (e.g., Ln 266, 365, 390).

15- Results section is extremely long (6+ pages of text without tables and figures) and needs to be condensed. Much of the data presented in the tables is re-introduced in text. Consider a figure in place of Table 2 to show changes over time and condense outcome variables with similar trends from Tables to show similarities and streamline the discussion. Text used to describe outcomes is very similar across many sections of the Results (e.g., 266-269 and 291-294).

16- Tables are difficult to read and decipher in the format currently inlayed within the text. Tables are also missing footnotes and units to define the variables.

17- Figure legends are missing to describe what population are displayed in Figure 1 and Figure 2.

18- Consider placement of Conclusion section prior to the Discussion section? Please check Journal layout and specifications.

19- Again, Discussion section is extremely lengthy (6+ pages) and needs to be condensed to summarize the outcomes and compare/contrast to literature in this area. Also, care to remove text and re-defining abbreviations already introduced again in the Discussion section.

20- How do the PA and overweight/obesity outcomes from your population compared to the University population without the influence of COVID-19? Are trends intensified for completely diverse?

21- The authors begin to compare how the study population compares with the adult or adolescent populations (post-COVID-19) previously published, realizing different environmental variables, etc. for consideration. However, data is not shown for level comparison, etc. Also, extraneous data provided on binge eating that is not covered in this study.

22- Authors should be cautious with sweeping conclusions without data to support from dietary intake and body image outcomes assessed in Lines 368-370.

23- Limitations section of the Discussion need to include the sample size used, missingness of data, etc.

Reviewer #5: Dear Author(s),

The current manuscript is not adding to the current literature. There are already studies as follows:

1-Ding, C., & Jiang, Y. (2020, December). The relationship between body mass index and physical fitness among Chinese university students: results of a longitudinal study. In Healthcare (Vol. 8, No. 4, p. 570).

2-Yu, H., An, S., Tao, Y., & Austin, L. (2022, September). Correlation and change in physical activity and physical fitness across four years of college students after one year of COVID-19 lockdown. In Healthcare (Vol. 10, No. 9, p. 1691).

3-Hao, Y., Lee, J., Wong, W. S. P., Wong, F. U. K., Hui, W. H. C., Leong, G. C. H., & Kong, Z. (2025). A longitudinal study to COVID-19 infection among university students: Physical fitness changes and psychological responses. Journal of Exercise Science & Fitness, 23(1), 7-13.

4-Martínez-de-Quel, Ó., Suárez-Iglesias, D., López-Flores, M., & Pérez, C. A. (2021). Physical activity, dietary habits and sleep quality before and during COVID-19 lockdown: A longitudinal study. Appetite, 158, 105019.

Regards

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Reviewer #1: No

Reviewer #2: Yes: Joanna Baj-Korpak

Reviewer #3: No

Reviewer #4: No

Reviewer #5: No

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Attachment

Submitted filename: PONE-D-25-29142 - rev.pdf

pone.0334088.s002.pdf^{(1.1MB, pdf)}

PLoS One. 2025 Oct 10;20(10):e0334088. doi: 10.1371/journal.pone.0334088.r002

Author response to Decision Letter 1

12 Aug 2025

Academic editor:

Journal Requirements:

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The author’s answer:

We confirm that the revised manuscript has been carefully formatted to meet all PLOS ONE style requirements. Specifically, we have: (1) adjusted the document structure to align with the journal’s template (e.g., title page, headings, reference style); (2) standardized file naming conventions as specified; and (3) ensured consistency in font, spacing, and section organization per the provided guidelines (https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne _formatting_sample_title_authors_affiliations.pdf). All changes have been verified to comply fully with the journal’s formatting policies.

Academic editor:

2. We note that the grant information you provided in the ‘Funding Information’ and ‘Financial Disclosure’ sections do not match.

When you resubmit, please ensure that you provide the correct grant numbers for the awards you received for your study in the ‘Funding Information’ section.

The author’s answer:

We sincerely apologize for the oversight in the initial submission. We have now carefully verified and corrected the grant information in both the ‘Funding Information’ and ‘Financial Disclosure’ sections to ensure complete consistency. The accurate grant numbers and funding details have been updated in the manuscript.

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Please include this amended Role of Funder statement in your cover letter; we will change the online submission form on your behalf.

The author’s answer:

The revised funder role statement has been indicated in red font in the cover letter.

Academic editor:

The author’s answer:

All expressions about the fund have been removed from the manuscript.

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5.PLOS requires an ORCID iD for the corresponding author in Editorial Manager on papers submitted after December 6th, 2016. Please ensure that you have an ORCID iD and that it is validated in Editorial Manager. To do this, go to ‘Update my Information’ (in the upper left-hand corner of the main menu), and click on the Fetch/Validate link next to the ORCID field. This will take you to the ORCID site and allow you to create a new iD or authenticate a pre-existing iD in Editorial Manager.

The author’s answer:

ORCID iDs have been validated in Editorial Manager.

Academic editor:

6.Your ethics statement should only appear in the Methods section of your manuscript. If your ethics statement is written in any section besides the Methods, please move it to the Methods section and delete it from any other section. Please ensure that your ethics statement is included in your manuscript, as the ethics statement entered into the online submission form will not be published alongside your manuscript.

The author’s answer:

The ethics statement is adjusted in the method section of the manuscript and removed from any other section.

Academic editor:

7. Please remove all personal information, ensure that the data shared are in accordance with participant consent, and re-upload a fully anonymized data set.

Note: spreadsheet columns with personal information must be removed and not hidden as all hidden columns will appear in the published file.

The author’s answer:

All personal information has been deleted to ensure that the data shared meets the consent of the participants.

Academic editor:

The author’s answer:

A title for the supporting information file has been added to the end of the manuscript and any text citations have been updated accordingly to match.

Academic editor:

We carefully evaluated the four references provided by the reviewers. Three of these are new documents [Ref 8, 19, 27] and one is a citation that we have already incorporated [Ref 26].

Point-by point responses

Reviewer 1�

1. Scientific Rigor and Methods:

The cohort design is appropriate for the research objectives, and the repeated physical fitness testing across four years is a strength.

The author’s answer:

We appreciate the reviewer’s constructive feedback. The rationale for using ANOVA has been clarified, emphasizing its suitability for comparing adjacent years while addressing within-group variability. Additionally, details on quality control measures (e.g., standardized testing procedures and calibrated equipment) have been added to strengthen the methodological rigor. These revisions enhance the transparency and robustness of the statistical analysis.

Reviewer 1�

2. Tables and Figures:

The author’s answer:

We appreciate the reviewer’s valuable suggestions regarding the presentation of tables and figures. In response, we have reformatted Tables 2, 3, and 4 to ensure proper alignment and improve header clarity for better readability.

In response to “reviewer 3” feedback, we have retained the original “3D scatterplots,” which were praised for their effective visualization of multidimensional relationships. To further improve interpretability, we have supplemented these with "boxplots" to better highlight temporal trends in BMI distribution. The "Results" section has been updated to incorporate both visualization methods, ensuring a more comprehensive and accessible presentation of the data. These modifications aim to balance innovative graphical representation with clear communication of distributional trends over time.

Reviewer 1�

3. Discussion Section:

The author’s answer:

We sincerely appreciate the reviewer’s constructive feedback regarding the need for a more structured and in-depth discussion. In response, we have thoroughly revised the Discussion section to provide a critical interpretation of the findings, including potential explanations for the observed trends in overweight and obesity rates. We have also incorporated comparisons with relevant existing studies to contextualize our results and added a clear acknowledgment of the study’s limitations, such as potential confounding factors and measurement constraints. These enhancements aim to improve the manuscript’s clarity, depth, and scholarly contribution. Specific modifications have been marked in red in the discussion section.

Reviewer 1�

4. Writing and Organization:

The author’s answer:

We have performed language polishing throughout the manuscript to enhance readability and precision. Additionally, we have improved section transitions and refined topic sentences in the Results and Discussion to ensure clearer logical progression. As suggested, we have also incorporated subheadings in the Discussion section to better structure the interpretation of findings.

Reviewer 1�

5. Ethics and Data Availability:

Ethical approval and informed consent are clearly stated.

Data availability is appropriately addressed and aligns with PLOS ONE standards.

Recommendation:

The author’s answer:

We sincerely appreciate the reviewer's positive assessment of our study's scientific validity and ethical compliance. In accordance with the recommendations, we have carefully revised the Ethics and Data Availability section to fully align with PLOS ONE standards, ensuring explicit transparency regarding ethical approval, participant consent, and data accessibility.

Reviewer 2�

Dear Authors,

Detailed suggestions are included in the comments on the article.

The author’s answer:

We sincerely appreciate the reviewers' thoughtful comments and valuable suggestions that have significantly strengthened our manuscript. In direct response to the expert's recommendations, we have enhanced Section 2.1 by explicitly stating that: (1) all researchers underwent standardized training to ensure measurement consistency and protocol adherence, and (2) all physical fitness assessments were conducted using uniform, calibrated measuring devices to guarantee data comparability across testing periods. These important additions address the methodological concerns regarding measurement reliability and procedural standardization while maintaining the study's original framework. The modifications improve the transparency and scientific rigor of our methods section without altering the fundamental study design. We fully acknowledge the limitation regarding regional representativeness in our discussion section and have incorporated the expert's suggestion about future use of accelerometers in our recommendations for further research.

Reviewer 3�

General Comments

Thank you for the opportunity to review this article, and I would like to congratulate the authors on their efforts in compiling this work.

However, the manuscript would benefit from further adjustments and revisions as proposed herein, section by section.

Title and Short Title

• The titles are clear and accurately reflect the study's content.

• I suggest you ensure consistency in the use of “pre/post-COVID-19” versus "before and after COVID-19" if used in other materials (e.g., in databases or indexing).

The author’s answer:

We thank the reviewer for this important observation regarding terminology consistency. In response, we have standardized all temporal references to COVID-19 throughout the manuscript, figures, and supplementary materials to exclusively use “before and after COVID-19” as the preferred terms.

Reviewer 3�

Abstract

• Be attentive to the use of capitalization; for instance, in line 28, the letter 'V' in the word "vital" should be capitalized. Review the entire document for any similar inconsistencies.

• Consider providing keywords at the end of the abstract to improve indexing and discoverability in academic databases and search engines.

The author’s answer:

We sincerely appreciate the reviewers' constructive feedback and have carefully addressed all suggestions: (1) we have substantially shortened the abstract (now 236 words) through tighter phrasing and removal of redundant information while preserving key findings; (2) all capitalization errors (including “Vital”) have been corrected throughout the manuscript; and (3) we have added 5 relevant keywords (COVID-19; physical fitness; body shape; university students; longitudinal study) at the end of the abstract to enhance discoverability.

Review

Attachment

Submitted filename: Response to Reviewers.docx

pone.0334088.s004.docx^{(52.7KB, docx)}

PLoS One. doi: 10.1371/journal.pone.0334088.r003

Decision Letter 1

Mohamed Ahmed Said

1 Sep 2025

PONE-D-25-29142R1A longitudinal study of four-year changes in physical fitness among university students before and after COVID-19: 2019-2022PLOS ONE

Dear Dr. Jiang,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands.Please carefully review the comments provided by Reviewer 4 and take the following steps in preparing your revised manuscript and response letter:

Address All Comments Point by Point

Prepare a detailed response document in which you reproduce each of Reviewer 4’s comments (in full or summarized clearly) and provide your corresponding response directly beneath it.
Ensure that every comment is addressed, even if it appears minor.
Revise the Manuscript Accordingly

Implement the required changes in the manuscript text where appropriate.
Highlight or track all revisions so that they are easily identifiable.

When You Agree with Reviewer 4

Clearly state how you have modified the manuscript in response to the reviewer’s suggestion.
Indicate the exact section(s) and line(s) where the changes were made.
When You Disagree with Reviewer 4

If you have a different opinion or cannot implement a specific suggestion, you must provide a clear and well-reasoned justification .
Support your position with relevant evidence, references, or methodological explanations.
Maintain a respectful and professional tone in explaining why the suggested change may not be applicable.

Overall Presentation

Organize your response letter systematically, following the same order of the reviewer’s comments.
Be concise but thorough in explaining your responses and changes.

Following these instructions will facilitate a transparent and constructive revision process, ensuring that all concerns raised by Reviewer 4 are appropriately addressed or justified.

Please submit your revised manuscript by Oct 16 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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We look forward to receiving your revised manuscript.

Kind regards,

Mohamed Ahmed Said, Ph.D.

Academic Editor

PLOS ONE

Journal Requirements:

1. If the reviewer comments include a recommendation to cite specific previously published works, please review and evaluate these publications to determine whether they are relevant and should be cited. There is no requirement to cite these works unless the editor has indicated otherwise.

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Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

Reviewer #4: (No Response)

Reviewer #5: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #4: Partly

Reviewer #5: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #4: I Don't Know

Reviewer #5: Yes

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4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #4: Yes

Reviewer #5: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #4: Yes

Reviewer #5: Yes

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6. Review Comments to the Author

Reviewer #1: Dear Authors,

I would like to commend you on your careful and thorough revision of the manuscript “A longitudinal study of four-year changes in physical fitness among university students before and after COVID-19: 2019–2022.” The manuscript has improved substantially, both in scientific rigor and in clarity of presentation, and I appreciate the diligence with which you have addressed prior reviewer and editorial feedback.

Strengths of the Revised Manuscript:

The four-year longitudinal design is a notable strength, providing a unique opportunity to capture pre-pandemic baselines, acute pandemic effects, and post-pandemic adaptations. This adds considerable value to the literature, where shorter-term studies predominate.

Methodological transparency has been improved, with clear descriptions of inclusion/exclusion criteria, standardized testing protocols, assessor training, equipment calibration, and testing conditions. These additions enhance the reproducibility and reliability of the findings.

Tables and figures are now clearer and easier to interpret. The combination of innovative 3D scatterplots with boxplots provides both depth and accessibility in data visualization.

The revised Discussion is more structured, with explicit contextualization in relation to existing studies, as well as a balanced acknowledgment of limitations and future research directions.

Language and organization have been polished, making the manuscript more concise and accessible without loss of technical depth.

Conclusion:

Overall, this is a well-executed study that makes a meaningful contribution to understanding the long-term effects of the COVID-19 pandemic on university students’ physical fitness. The revisions have addressed previous concerns comprehensively, and the manuscript now meets the criteria for publication. I support its acceptance after minor editorial checks.

Congratulations on your careful work, and I look forward to seeing this valuable study published.

Reviewer #2: The Authors have responded appropriately to my suggestions and comments made in the previous round of reviews. They have answered my questions. In my opinion, this manuscript is now suitable for publication.

Reviewer #4: The main concern of this version of the manuscript is the lack of the authors to address the Reviewer comments. A major concern is the lack of transparency of the attrition of study participants and missingness of data. Many other concerns some again for the second time have been detailed to help provide insight to the authors.

SPECIFIC RECOMMENDATIONS:

1- Again, as asked in first review please revisit the use of gender vs. sex throughout. Currently both are used inter changeably [Ln 81,89,120,192,199,200]. Did you have transgender study participants? If so, consider use of gender otherwise correct use should be sex throughout.

2- Is the takeaway just for health planning purposes? Or to better prevent and treat long-term health outcomes related to PA? [Ln 83-84; 90-91].

3- Lines 101-107 read like a bulleted listing; needs to be integrated with the rest of the paragraph. In summary, ‘a convenience sample of available and interested incoming freshman class of 2019 admission with limited pre-existing health (e.g., ….) or physical conditions that may limit exercise participation’?

4- It would be helpful for transparency if the authors included number of students/study participants remaining in study (data used) at each stage/year of the study in the Results similar to how you set up in Methods [Ln 113-116]. Is Table 2 correct? 1206 males and 3207 females remained in the study all 4 years? There was no drop out or data loss? Please make this clear in your Methods or Results section.

5- Consider relocating details about testing administrators (e.g., physical education professors) from section 2.1 to Ln 125 or later for consistency. Were test administrators consistent throughout the study? This was asked in last review and not included in revision.

6- Again, as asked in earlier review and authors did not respond or update Methods section 2.2 should define environmental conditions (e.g., room temperature and humidity ?) and testing groups participants were included in. These can greatly impact and bias outcomes (e.g., control for competitive nature of participants were controlled throughout sessions)

7- Ln 141 is ‘blowing’ correct terminology to be used here?

8- Ln 142 define ‘better’ here when decerning between two scores. Was there a pre-determined range?

9- Ln 165 is ‘barbell’ correct terminology to be used here? Should text read ‘final number of pull-ups were recorded’?

10- Define ‘coach’ in Ln 169, 175, (is this Physical Education Professor)? Also, can simplify text to “recorded time was rounded to nearest tenths of second”.

11- Word missing in Ln 173 ‘was’

12- Is 1000m identical to 800m or 50m protocol? Please specify.

13- Ln 194-196 need to be added to Limitation section 4.4. in Discussion if not accounted for in the statistical analysis. Overlooking these confounding variables can greatly skew outcomes and interpretation.

14- Ln 204 were individual data collectors consistent throughout the study? If not, please add interindividual variability of raters to your limitations section 4.4 in Discussion.

15- Tables 2 & 3 please add lines or shading for ease of reading, variable units of measure, and round values to significantly meaningful decimal place with consistency in Table 2.

16- Trends are similar across sex and some performance outcomes reported in section 3.2.2. Suggest combining outcomes that are similar in trend into paragraphs when detailing Table 2 for simplicity and streamline Results section.

17- Again, as asked in original review figures are incomplete – axis labels and legends are missing to describe what population are displayed in Figure 1 and Figure 2.

18- Consider removing Figures 3 & 4 since Figures 1 &2 show same data.

19- Reconsider use of ‘body shape’ as it misleads the reader (ex., header 4.1 and section). Authors did not measure any body lengths or circumferences. BMI is considered body size as is height and weight.

20- Ln 352-355 define the populations cited.

21- Consider a more appropriate reference for statement in Ln 357.

22- Ln 372-375 is the female to male ratio of students documented to be higher in the University selected in this study? This ration/proportion of population statistics should be stated.

23- Could differences across sex found in 50m run and sit-ups be linked to social norms and females becoming more familiarized with ‘working out’ in the University setting? There is work discussing this both in the civilian and military communities. Female may have a greater breath of improved performance because they start at a lower threshold than capable of achieving. Consider reviewing literature and citing in Discussion.

24- PA is defined in Ln 391, consider moving this earlier in the paper and use throughout.

25- Section 4.4. needs to be added to include the significant disproportion of females in the study population skewing results, and items called out in Items # 6,13, and 14.

26- Lastly, and most importantly in Ln 438 data missingness is presented as a limitation however nowhere in the manuscript is the attrition or missing data discussed. This needs to be addressed and authors need to be transparent with sample size across the four years.

Reviewer #5: Dear Author(s),

The paper is better and has improved. From abstract to references and tables and figures are revised accordingly.

Regards

**********

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Reviewer #1: No

Reviewer #2: Yes: Joanna Baj-Korpak

Reviewer #4: No

Reviewer #5: Yes: Ferhat Esatbeyoglu

**********

PLoS One. 2025 Oct 10;20(10):e0334088. doi: 10.1371/journal.pone.0334088.r004

Author response to Decision Letter 2

14 Sep 2025

Dear Editors and reviewers

On behalf of all the contributing authors, I would like to express our sincere appreciations of your letter and reviewers' constructive comments concerning our article entitled “A longitudinal study of four-year changes in physical fitness among university students before and after COVID-19: 2019-2022” (Manuscript No:PONE-D-25-29142R2). These comments are all valuable and helpful for improving our article. Based on the comments of the editor-in-chief and reviewers, we made extensive revisions to the manuscript.In this revised version. changes to our manuscript were all highlighted within the document by using red-colored text.Point-by point responses to the nice editor and four nice reviewers are listed below this letter.

Point-by point responses

Reviewer 1�

Strengths of the Revised Manuscript:

Tables and figures are now clearer and easier to interpret. The combination of innovative 3D scatterplots with boxplots provides both depth and accessibility in data visualization.

The revised Discussion is more structured, with explicit contextualization in relation to existing studies, as well as a balanced acknowledgment of limitations and future research directions.

Language and organization have been polished, making the manuscript more concise and accessible without loss of technical depth.

Conclusion:

Congratulations on your careful work, and I look forward to seeing this valuable study published.

The author’s answer:

Thank you very much for your thoughtful and encouraging feedback on our revised manuscript, "A longitudinal study of four-year changes in physical fitness among university students before and after COVID-19: 2019–2022." We are truly grateful for your recognition of the efforts made to strengthen the manuscript's scientific rigor, clarity, and overall presentation.

We especially appreciate your positive comments regarding the longitudinal design, methodological transparency, improved data visualization, and the more structured and contextualized Discussion. It is very rewarding to know that the revisions have successfully addressed the previous concerns and enhanced the reproducibility, accessibility, and contribution of the study.

Your supportive conclusion and recommendation for acceptance are greatly encouraging. We are pleased to learn that the manuscript now meets the publication standards and will gladly cooperate with any minor editorial checks required.

Thank you once again for your time, insightful suggestions throughout the review process, and kind words.

Reviewer 2�

Thank you very much for your positive feedback and for confirming that our responses to your previous comments and suggestions are satisfactory. We greatly appreciate your time and insightful input throughout the review process, which has significantly improved the quality of our manuscript. We are pleased to know that you now consider the manuscript suitable for publication.

Reviewer 4�

1-Again, as asked in first review please revisit the use of gender vs. sex throughout. Currently both are used inter changeably [Ln 81,89,120,192,199,200]. Did you have transgender study participants? If so, consider use of gender otherwise correct use should be sex throughout.

The author’s answer:

Thank you for raising this point. We have carefully reviewed the use of “gender” and “sex” throughout the manuscript. As our study did not include any transgender participants, we have replaced all instances of “gender” in the specified lines (81, 89, 120, 192, 199, 200) and elsewhere in the text with the term “sex”. The manuscript has been updated accordingly.

Reviewer 4�

2-purposes? Or to better prevent and treat long-term health outcomes related to PA? [Ln 83-84; 90-91].

The author’s answer:

In the first modification, the phrase “long-term trends” was refined to “sustained trends” for terminological precision, while the scope of the “distinction” was expanded using “not only for... but also for...” to emphasize its critical role in shaping targeted strategies for managing PA-related health consequences. [Ln83-85]

In the second sentence, “for policymakers about” was strengthened to “to guide policymakers in”, enhancing the actionable nature of the evidence, and the vague “health impacts” was replaced with “preventing and mitigating long-term health outcomes associated with reduced physical activity”, thereby directly linking pandemic measures, PA reduction, and health outcomes as suggested by the reviewer. Both changes improve clarity, align with the commentary, and underscore the policy-responsive and intervention-oriented value of the study. [Ln91-93]

Reviewer 4�

The author’s answer:

We thank the reviewer for this suggestion. The selection criteria description has been revised to improve integration within the paragraph, removing the bulleted-list format and presenting the information in a cohesive narrative form. The description now more clearly characterizes the sample as a convenience sample of available and interested freshmen with specific exclusions for health or physical conditions affecting exercise.[Ln104-111]

Reviewer 4�

4-It would be helpful for transparency if the authors included number of students/study participants remaining in study (data used) at each stage/year of the study in the Results similar to how you set up in Methods [Ln 113-116]. Is Table 2 correct? 1206 males and 3207 females remained in the study all 4 years? There was no drop out or data loss? Please make this clear in your Methods or Results section.

The author’s answer:

We thank the reviewer for raising this important point. We have now clarified the participant flow and retention details in the Methods section. Specifically, we have explicitly stated the initial number of participants, the number of dropouts over the study period, the reasons for attrition, and the final number of students (4413) with complete data for all four years. This revision enhances the transparency of our cohort's trajectory and confirms that the numbers presented in Table 2 reflect the participants with complete longitudinal data.[Ln120-125]

Reviewer 4�

The author’s answer:

Thank you for this suggestion. We have relocated the details regarding the test administrators from section 2.1 to the methodological description of the testing procedures (as now reflected around line 125 in the revised manuscript) to improve the logical flow and consistency of information. We have also explicitly stated that the same team of trained professors conducted all assessments across all four years, directly addressing the previously raised question about the consistency of the testing personnel.

Reviewer 4�

The author’s answer:

We thank the reviewer for this important feedback. We have now updated the Methods section (2.2) to include detailed information about the controlled environmental conditions (specifying room temperature and humidity ranges). These additions address potential confounding factors and enhance the reproducibility of our study protocol.[Ln138-139]

Reviewer 4�

7- Ln 141 is ‘blowing’ correct terminology to be used here?

The author’s answer:

Thank you for pointing this out. We have replaced the informal term “blowing” with the more precise and clinically appropriate terminology “exhalation maneuver” to accurately describe the spirometry procedure and enhance the scientific rigor of the manuscript.[Ln152]

Reviewer 4�

8- Ln 142 define ‘better’ here when decerning between two scores. Was there a pre-determined range?

The author’s answer:

We appreciate the reviewer’s comment for clarity. The term “better” has been replaced with the more objective and quantifiable term “higher” to describe the selection of scores, and we have explicitly noted that this was determined according to a pre-defined standardized scoring protocol, thereby eliminating any potential ambiguity.[Ln153-155]

Reviewer 4�

9- Ln 165 is ‘barbell’ correct terminology to be used here? Should text read ‘final number of pull-ups were recorded’?

The author’s answer:

We thank the reviewer for these precise suggestions. We have replaced the potentially ambiguous term “barbell” with the more accurate term “bar”, clarified the movement standard using the phrase "chins cleared the horizontal level of the bar," and rephrased the recording method to “the final number of correctly completed pull-ups was recorded” to enhance terminological and methodological precision.

Reviewer 4�

10- Define ‘coach’ in Ln 169, 175, (is this Physical Education Professor)? Also, can simplify text to “recorded time was rounded to nearest tenths of second”.

The author’s answer:

We thank the reviewer for these constructive suggestions. We have replaced the informal term “coach” with the more precise “physical education professor” throughout the text to maintain consistency with our methodology description, and have simplified the timing description to “recorded time was rounded to the nearest tenth of a second” for improved clarity and conciseness.[Ln183、189、191]

Reviewer 4�

11- Word missing in Ln 173 ‘was’

The author’s answer:

We thank the reviewer for this careful observation. The missing word “was” has been added to ensure grammatical correctness, and the sentence now reads: “Each participant completed two trials, with the better performance was recorded.”

Reviewer 4�

12-Is 1000m identical to 800m or 50m protocol? Please specify.

The author’s answer:

Thank you for raising this point for clarification. We have explicitly specified that the 1,000-meter run protocol was identical to the 800-m and 50-m runs in its starting procedure, timing method, and rounding rule to ensure consistency and clarity in the description of methodological protocols across all running tests.[Ln193-195]

Reviewer 4�

The author’s answer:

We sincerely thank the reviewer for this insightful comment. We have now added the point regarding the potential confounding variables (age, baseline fitness, and socioeconomic status) to the Limitations section (Section 4.4) as suggested. This addition strengthens our discussion by acknowledging these important factors that could influence the interpretation of the results.[Ln]

Reviewer 4�

14- Ln 204 were individual data collectors consistent throughout the study? If not, please add interindividual variability of raters to your limitations section 4.4 in Discussion.

The author’s answer:

Thank you for this valuable comment. We agree that the consistency of data collectors is an important methodological consideration. In response to your feedback, we have revised the Limitations section (4.4) of the Discussion to explicitly acknowledge that multiple data collectors were involved due to the large scale and long duration of the study, and that this may have introduced inter-rater variability despite efforts to standardize protocols. The added sentence reads: "Furthermore, due to the large number of test items and participants, multiple data collectors were involved throughout the study period. Despite efforts to standardize protocols, this may have introduced inter-rater variability." We believe this addition strengthens the manuscript by providing a more comprehensive overview of the study's limitations.

Reviewer 4�

15- Tables 2 & 3 please add lines or shading for ease of reading, variable units of measure, and round values to significantly meaningful decimal place with consistency in Table 2.

The author’s answer:

Thank you for your constructive suggestions regarding the presentation of data in Tables 2 and 3. We have revised both tables accordingly by adding grid lines to enhance readability and to clearly delineate the data. Furthermore, we have ensured that all values in Table 2 are rounded to a consistent and statistically appropriate number of decimal places, and we have explicitly stated the units of measure for all relevant variables in the table headers.

Reviewer 4�

The author’s answer:

Thank you for your constructive suggestion. We have revised the Results section to combine outcomes with similar trends into more concise paragraphs, as recommended. The descriptions of vital capacity, long-jump, sit-reach, and endurance running tests have been grouped to improve clarity and flow, while all key statistical findings and temporal patterns have been retained.

Reviewer 4�

17- Again, as asked in original review figures are incomplete – axis labels and legends are missing to describe what population are displayed in Figure 1 and Figure 2.

The author’s answer:

We have now updated both Figure 1 and Figure 2 to include all necessary axis labels and legends to clearly describe the displayed populations and ensure the figures are complete and easily interpretable.

Reviewer 4�

18- Consider removing Figures 3 & 4 since Figures 1 &2 show same data.

The author’s answer:

Thank you for your suggestion. We agree that Figures 1 and 2 effectively present the same data as Figures 3 and 4. Therefore, we have removed Figures 3 and 4 from the manuscript to avoid redundancy and improve clarity.

Reviewer 4�

19-Reconsider use of ‘body shape’ as it misleads the reader (ex., header 4.1 and section). Authors did not measure any body lengths or circumferences. BMI is considered body size as is height and weight.

The author’s answer:

Thank you for this important feedback. We agree that the term "body shape" was misleading, as it implies measurements such as lengths or circumferences that were not conducted in our study. We have replaced "body shape" with the more accurate term "body size" throughout the manuscript, including in the header of section 4.1,

Attachment

Submitted filename: Response_to_Reviewers_auresp_2.docx

pone.0334088.s005.docx^{(34.6KB, docx)}

PLoS One. doi: 10.1371/journal.pone.0334088.r005

Decision Letter 2

Mohamed Ahmed Said

23 Sep 2025

A longitudinal study of four-year changes in physical fitness among university students before and after COVID-19: 2019-2022

PONE-D-25-29142R2

Dear Dr. Jiang,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Mohamed Ahmed Said, Ph.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewer #4:

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #4: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #4: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #4: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #4: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #4: Yes

**********

6. Review Comments to the Author

Reviewer #4: The authors have addressed all concerns appropriately in this second revised version. One last edit is required on Line 236 to update section header 3.2.1 from ‘Body Shape’ to ‘Body Size.’

**********

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Reviewer #4: No

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PLoS One. doi: 10.1371/journal.pone.0334088.r006

Acceptance letter

Mohamed Ahmed Said

PONE-D-25-29142R2

PLOS ONE

Dear Dr. Jiang,

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now being handed over to our production team.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

S1 File. Supplementary material.

(DOCX)

pone.0334088.s001.docx^{(99.8KB, docx)}

Attachment

Submitted filename: PONE-D-25-29142 - rev.pdf

pone.0334088.s002.pdf^{(1.1MB, pdf)}

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Submitted filename: Response to Reviewers.docx

pone.0334088.s004.docx^{(52.7KB, docx)}

Attachment

Submitted filename: Response_to_Reviewers_auresp_2.docx

pone.0334088.s005.docx^{(34.6KB, docx)}

Data Availability Statement

All relevant data are within the paper and its Supporting Information files.

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PERMALINK

A longitudinal study of four-year changes in physical fitness among university students before and after COVID-19: 2019–2022

Liangru Guo

Liang Jiang

Huizhi Huang

Roles

Abstract

Background

Methods

Results

Conclusions

1 Introduction

2 Materials and methods

2.1 Study population

2.2 Physical fitness test

2.2.1 Vital capacity.

2.2.2 Long-jump.

2.2.3 Sit-reach.

2.2.4 Pull-ups.

2.2.5 Running tests (50-m, 800-m, and 1,000-m Runs).

2.2.7 Body mass index (BMI).

2.3 Statistical analysis

3 Results

3.1 Demographic characteristics of participants

Table 1. Demographic characteristics.

3.2. Results of ANOVA for university students’ physical fitness

3.2.1 Changes in body shape.

Table 2. Results of ANOVA.

3.2.2 Changes in physical fitness.

3.3 Detection of overweight and obesity among university students

3.3.1 Detection of obesity.

Fig 1. Boxplot of Female BMI Distribution (2019–2022).

Fig 2. Boxplot of Female BMI Distribution (2019–2022).

Table 3. Comparison of obesity detection rates.

3.3.2 Detection of overweight.

Table 4. Comparison of overweight detection rates.

4 Discussions

4.1 Changes in the body size of college students

4.2 Changes in the physical fitness of university students

4.3 Practical implications

4.4 Limitations and future research directions

5 Conclusions

Supporting information

Data Availability

Funding Statement

References

Decision Letter 0

Mohamed Ahmed Said

Roles

Author response to Decision Letter 1

Decision Letter 1

Mohamed Ahmed Said

Roles

Author response to Decision Letter 2

Decision Letter 2

Mohamed Ahmed Said

Roles

Acceptance letter

Mohamed Ahmed Said

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

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