Dose-response effects of 8-week resistance training on body composition and muscular performance in untrained young women: A quasi-experimental design

Abstract

Background:

The purpose of this study was to investigate the effects of 8-week resistance training with different training volumes on body composition, maximum strength, peak power, and muscle thickness in non-training women.

Methods:

This was a 3-arm, prospectively designed, randomized controlled trial. A total of 45 adult women aged 20.7 ± 1 years, the mean heights of the participants were 166 ± 0.07 cm, body weight was measured as 54.5 ± 8.8 kg, and body mass index was 19.9 ± 2.1 kg/m². They were randomized to low-volume training resistance training (LVT; n = 15, 3 sessions of 12 exercises per week), moderate-volume training resistance training (MVT; n = 15; 4 sessions of 12 exercises per week), and high-volume resistance training (HVT; n = 15; 5 sessions of 12 exercises per week) for 8 weeks. The muscle thickness (MT) of the vastus lateralis was assessed at baseline and 8 weeks later using a portable ultrasound device.

Results:

A total of 39 adult women completed the study, with 2 participants from each group lost to follow-up. All experimental groups 1RM increased (P = .001, effect size (ES) = 0.463) All groups showed improved muscle thickness (MT) (P = .001) and CMJ (P = .004). The group × time interaction is statistically significant (P = .001) suggests that the changes in muscle thickness over time differ significantly between the different training volume groups (η_p²) is 0.368.

Conclusion:

In untrained young women, resistance training improved muscle hypertrophy, maximal strength, power, and body composition in untrained young women. However, 4 sessions MVT per week were superior to LVT and HVT sessions, suggesting a nonlinear dose-response relationship favoring moderate volume over low or high volumes, at least in previously untrained young women.

Trial Registration:

ClinicalTrials.gov (NCT06449300)

1. Introduction

Building and maintaining skeletal muscle mass and strength throughout life is a well-known aspect of a healthy lifestyle. Skeletal muscles generate the contraction force required for locomotor movements, such as joint motion, and it is well known that persons with a higher skeletal muscle-to-total body mass ratio have a better chance of surviving and recovering from numerous illnesses.^[1–4] Unfortunately, sedentary lifestyles and aging cause changes in muscular dysfunction (muscle mass, strength, and physical function).^[5–7] After the age of 30 years, muscle mass declines by 3% to 8% every decade,^[8] and on average, one loses 0.2 kg a muscle mass per year.^[9,10] The average loss in lean weight is 0.2 kg per year,^[11] increasing to 0.4 kg per year by the fifth decade of life.^[12] Muscle mass loss is a major concern among the elderly and sedentary.^[13]

According to the latest ACSM’s Worldwide Fitness Trends, resistance training (RT) is one of the most popular fitness activities globally.^[14] It consistently ranks among the top fitness trends, reflecting its widespread adoption due to its effectiveness in improving muscular strength, endurance, and overall physical fitness. This trend aligned with the most popular health and fitness trends in Turkey that reported the popularity of the resistance training.^[15] This increase is attributed to growing awareness of the health benefits of strength training, including improved body composition, enhanced metabolic rate, and reduced risk of chronic diseases. This emphasizes the importance and appeal of resistance training in modern fitness regimes. Resistance exercise is the most significant approach to prevent, protect, and increase skeletal muscle mass loss is resistance exercise.^[16] Researchers have encouraged moderate resistance exercise for healthy living,^[17] and studies have demonstrated that resistance training maintains muscle building in men and women of all ages.^[18]

RT is essential for prevention and treatment of various diseases.^[19–22] In this context, RT improves cardiovascular health and bone mineral density,^[23] reduces blood pressure,^[21] and reverses specific aging factors in skeletal muscle.^[17] It is well known that RT has a positive effect on muscle growth and strength when performed repeatedly.^[23,24] RT has been established as an efficient stimulus for muscular strength and hypertrophy.^[22,25,26] In addition, RT significantly improves motor characteristics such as sprint and strength.^[27,28] Previous studies have established that RT can improve body composition in untrained, young,^[29,30] older,^[31,32] and female subjects, among other impacts of RT. Another study found that RT improved anthropometric measures, body composition, and physical performance in women with abdominal obesity.^[33] Different RT programs control factors, such as volume, intensity, and frequency, which enhance muscle growth.^[34] The number of repetitions × number of sets × load intensity product is a common definition for RT volume; however, there are different ways to characterize volume or total workload.^[35] Resistance workouts have been shown to lower resting systolic and diastolic blood pressures.^[36] Most critically, both systolic blood pressure and diastolic blood pressure decline appear to be proportional to training volume.^[36] According to 1 study, higher exercise volumes than smaller exercise volumes resulted in greater decreases in systolic blood pressure and diastolic blood pressure in hypertensive individuals.^[37]

Studies have suggested that different protocols obtain similar results for the total training volumes.^[30,38] However, it is possible that volume generates nonlinear dose-response relationships; that is, there may be a threshold after which greater volumes produce worse results. Moreover, these relationships may vary depending on training status (e.g., athletes vs untrained subjects). This study aimed to examine the effects of low-volume (LVT), moderate-volume (MVT), and high-volume (HVT) resistance training on body composition, maximal strength, peak power, and muscle thickness (MT) in untrained women, which represent a large part of the population. We hypothesized that an ideal training volume for optimal muscle development would be found in the MVT group. An 8-week period was defined, as this seems to be sufficient to achieve a significant increase in muscle strength in both men and women.^[39] Considering the information in the literature, the aim of this study was to examine the effects of low-volume, moderate-volume, and high-volume resistance training on muscle thickness, the effects of different resistance training volumes on the maximum strength gain, and the effects of different training volumes on strength gains.

2. Methods

2.1. Participants

Inclusion criteria for the study were as follows: young female adults aged between 18 and 30 years, who were healthy and free from any cardiovascular or metabolic disorders. Participants were required to be nonsmokers and not pregnant at the time of the study. Additionally, they should have been classified as physically inactive. The untrained women criteria specify that participants as physically inactive, defined according to WHO guidelines which defines physical inactivity as not meeting the recommended levels of physical activity, which includes engaging in <150 minutes of moderate-intensity aerobic activity per week or 75 minutes of vigorous-intensity activity.^[15,40] Exclusion criteria included any history of cardiovascular or metabolic disorders, current smoking status, and pregnancy. Women who had participated in structured physical exercise programs prior to the study or engaged in regular resistance training or physical active within the past 6 months were also excluded from the study.

A sample of healthy but untrained young adult female college students (n = 50) participated in the study, and 39 completed the training (11 participants dropped out for various reasons unrelated to the interventions). The sample size was calculated using G* power software (version 3.0.1) with a target effect size of 0.25, alpha of 0.05, and power of 0.95, resulting in an estimated sample size of at least 12 participants per group.^[41] The participants in the 8-week resistance training (RT) program had mean age of 20.3 ± 1.1 years, 20.6 ± 1.0 years, and 21.2 ± 0.9 years for the LVT, MVT, and HVT groups, respectively. The mean heights of the participants were 166 ± 0.05 cm for the LVT group, 165 ± 0.06 cm for the MVT group, and 167 ± 0.08 cm for the HVT group. Mean body weight was measured as 54.8 ± 6.5 kg, 53.9 ± 3.9 kg, 54.9 ± 7.2 kg, and body mass index (BMI) as 19.8 ± 1.9 kg/m², 19.8 ± 1.7 kg/m², and 20.7 ± 2.7 kg/m², respectively. The exclusion criteria were intake of performance-enhancing drugs, anabolic steroids, injury, physiological or physical limitations that could affect the ability to perform training, and physical testing in the year before the start of the study. In addition, those who had undergone RT for > 2 months in the previous 6 months were excluded.

2.2. Study design

Healthy female adults voluntarily participated in this randomized controlled trial. Following baseline measurements, the participants were randomized into 3 groups. The random allocation sequence was implemented using sequentially numbered, opaque, sealed envelopes in a 1:1:1 ratio. Each envelope contained the assignment to one of the 3 study groups: low-volume training (LVT), moderate-volume training (MVT), or high-volume training (HVT). To maintain allocation concealment until the interventions were assigned, the envelopes were prepared and sealed by an independent researcher who was not involved in participant recruitment or intervention administration. At the time of assignment, each participant selected an envelope in sequential order. The flowchart of the participants is shown in Figure 1. All participants were informed of the risks and benefits of the study and signed an informed consent form.

Figure 1.

Participant flow diagram. HVT = high-volume training, LVT = low-volume training, MVT = moderate-volume training.

A quasi-experimental design was conducted for this study which including 3 study arms: low-volume (LV), moderate-volume (MV), and high-volume (HV) resistance training groups. This study was conducted in accordance with the Declaration of Helsinki and approved by the Kirikkale University Research Ethics Committee (2021.11.07). The study protocol was registered at ClinicalTrials.gov (ID NCT06449300).

2.2.1. Randomization and blinding

After baseline assessments, participants were randomly assigned to one of the groups (HVT, MVT, or LVT). Group 1 received a HVT of resistance exercise for 5 times per week.; group 2 received an MVT regime with resistance training prescribed in each training session identical to that of HVT but for 4 times per week; group 3 was the LVT group that received RT for 3 times per week. A random allocation sequence was performed by an independent research assistant. Trained assessor, who were blinded to the study conditions, conducted the physical examinations to determine the research outcomes. The randomization process, alongside the detailed protocol for training and testing, ensured that the groups were comparable and that any differences observed could be attributed to the varying volumes of training rather than other confounding factors.

Following randomization, all 3 groups completed LVT, MVT, and HVT at the fitness center for 8 weeks of resistance training. Additionally, the use of a split strength-training method and a standardized training regimen for all groups allowed for a rigorous examination of the effects of different training volumes on the outcomes of interest. Participants were instructed to continue their regular daily activities and refrain from modifying the training throughout the study period. Two weeks prior to the start of the training, the participants were given a laboratory visit and detailed information about the tests. The tests were conducted at university research laboratories. The testing week was held 1 week before the training sessions. All tests were performed after warm-up and familiarization. All laboratory tests were performed at the same time of the day under stable environmental conditions (23°C, 52–62% relative humidity).

In this study, a split strength-training method was applied to assess the impact of different training frequencies.^[42] Participants were divided into 3 groups based on their training frequency: the Low-Volume Group (LVG) trained 3 times per week, the Moderate-Volume Group (MVG) trained 4 times per week, and the High-Volume Group (HVG) trained 5 times per week.

Individual training loads for each participant were determined based on their personal 1 repetition maximum (1RM). The 1RM assessment was conducted following a previously detailed methodology.^[41,42] The testing commenced with a warm-up sequence consisting of 3 sets. Initially, participants performed 8 to 10 repetitions using a lightweight load (approximately 50% of 1RM). This was followed by a set of 3 to 5 repetitions with a medium-weight load (about 75% of 1RM). The warm-up concluded with 1 to 3 repetitions using a heavyweight load (about 90% of 1RM). After completing the warm-up, each subject underwent 1RM testing. This evaluation involved gradually increasing the weight during consecutive attempts until the individual was no longer able to perform a proper lift, achieve full range of motion, or maintain correct technique. The 1RM assessment typically encompassed about 5 sets of single repetitions, with rest intervals of 3 to 5 minutes. This method ensured an accurate measurement of each participant’s maximum strength capacity.), which was assessed before the study began. To ensure proper exercise execution, all workouts were conducted under the supervision of certified trainers. Each session lasted approximately 60 minutes and followed a consistent training prescription of 3 sets of 8–12 repetitions per exercise, with 120-second rest intervals between sets. The training loads were systematically increased by 5% each week for all participants. After the 8-week interventions, the outcomes were evaluated across the 3 groups.

2.3. Diet analysis

To account for any dietary effects, the participants were instructed not to modify their diet or reduce their calorie intake during the trial, and they were required to eat all their meals at the same location to encourage muscle growth. The participants maintained a 3-day dietary journal before and after the trial. Two weekdays and 1 weekend day comprised a 3-day food diary. Each participant was given detailed instructions on how to complete a food diary before starting the experiment. Subsequently, the researchers assessed the food diaries and explained any misunderstandings. The BeBiS nutrition analysis computer application was used to examine the food diaries (BeBiS software program; BeBiSpro for Windows, Stuttgart, Germany; Turkish Version BeBiS 4). The same researcher (blinded to the interventions) assessed all the food diaries.

2.4. Anthropometric measurements

A wall-mounted stadiometer was used to measure the height of the participants (Seca 217 stadiometer, Hamburg, Germany), which features a precision of 0.1 cm. The participant was instructed to stand barefoot with their heels and head aligned horizontally to ensure accurate height measurement. Body mass was assessed using the Tanita body composition analysis system (Tanita BC418MA Analyzer Tanita Corp., Tokyo, Japan). This device provides measurements with an accuracy of up to 0.1 kg and a high intraclass correlation coefficient (ICC) ranging from 0.81 to 0.95, reflecting its reliability.^[43]

2.5. Muscle thickness measurements

Muscle thickness was determined using the GE Healthcare VScan portable ultrasound scanner (General Electric Company, Boston). This device offers real-time imaging capabilities for precise measurement of muscle thickness. The muscle thickness was measured in the quadriceps femoris (vastus lateralis) at a specific location between the greater trochanter and lateral epicondyle of the thigh. The measurement process involved applying a thin layer of gel to the skin to ensure proper acoustic coupling, placing the ultrasound probe gently on the skin, and moving it across the muscle to capture images. The probe was pressed softly to avoid altering muscle thickness. Three images were obtained for each measurement, and the average thickness from the bone to the superficial sarcolemma was recorded. The ICC for muscle thickness measurements ranged from −0.22 to 0.84, indicating variability in measurement reliability.^[44,45]

2.6. Peak power and jump height measurement

The Accupeak power2.0 portable force platform system (Accupeak power2.0, Massachusetts) was used to measure peak power and vertical jump height. This device operates with a measurement frequency of 500 Hz, allowing for high-resolution data collection. Participants performed the Countermovement Jump (CMJ) following a standardized 10-minute warm-up. They executed 3 jumps on the force platform, with a 5-minute rest interval between each jump. During the jump, participants were instructed to use their arms freely, start the downward movement upon hearing a tone from the computer, and jump as high as possible.^[27,46] Both feet needed to remain on the platform until the computer beeped to signal the end of the measurement. The highest values for CMJ height and peak power, recorded in watts, were used for analysis. The ICC for peak power measurements ranged from 0.50 to 0.76, demonstrating moderate to good reliability.^[27,46]

3. Statistical analysis

The mean and standard deviation of all the data from the study participants were calculated. The “Shapiro–Wilk” test was used to check whether the data had a normal distribution, and 2-way repeated measures ANOVA was performed. In addition, the anthropometric characteristics, ultrasound measurements, vertical jump measurements, peak force values, first and last 1RM force measurements, percent change values (%), and differences (Δ) of the study participants are shown in the tables. Partial eta squared values (η_p²) of test scores were calculated to obtain effect sizes (ES), with values > 0.01 considered a small effect, >0.06 a moderate effect; and > 0.14 a large effect.^[47] Statistical data were analyzed using SPSS version 28.0 (IBM Corp., Armonk) for Windows. Statistical significance was set at P < .05.

4. Results

A total of thirty-nine women with a mean age of 20.3 ± 1.1 years (n = 13), 20.6 ± 1.0 years (n = 13), and 21.2 ± 0.9 years (n = 13) for low volume training (LVT, 3 sessions of 12 exercises per week), moderate volume training (MVT; 4 sessions of 12 exercises per week), and high volume training (HVT; 5 sessions of 12 exercises per week) resistance training (RT), respectively. Overall women mean age is 20.7 ± 1 years, with mean heights of 166 ± 0.07 cm, body weight measured as 54.5 ± 8.8 kg, and BMI calculated as 19.9 ± 2.1 kg/m². At baseline, no significant differences were observed among groups in any dependent variables (Table 1).

Table 1.

Descriptive characteristic and total daily nutrient intakes from food diaries for all group.

Variables	LVT	MVT	HVT	P value
Age (yr)	20.3 ± 1.1	20.6 ± 1.0	21.2 ± 0.9	.21
BMI (kg/m2)	19.8 ± 1.7	19.8 ± 1.9	20.7 ± 2.8	.57
Height (cm)	166 ± 0.05	165 ± 0.06	167 ± 0.08	.61
Energy (kcal)	1410 ± 470	1615 ± 423	1804 ± 658	.177
Kcal/kg	24.8 ± 10.3	29.6 ± 9.3	33.3 ± 13.9	.177
Protein (g/d)	62.0 ± 21.6	68.9 ± 19.6	70.0 ± 17.6	.537
Protein (%)	18.0 ± 4.3	17.3 ± 3.5	16.9 ± 5.7	.811
Protein (g/kg)	1.1 ± .9	1.3 ± .4	1.3 ± .3	.377
CHO (%)	49.6 ± 11.4	46.8 ± 7.0	49.2 ± 5.1	.659
CHO (g/d)	175.9 ± 69.6	186.0 ± 45.4	227.1 ± 103.6	.212
CHO (g/kg)	3.1 ± 1.5	3.4 ± .9	4.2 ± 2.1	.222
Fat (%)	32.4 ± 10.1	33.9 ± 5.5	33.9 ± 5.4	.476
Fat (g/d)	50.9 ± 21.9	66.2 ± 25.3	68.5 ± 25.9	.152
Fat (g/kg)	.9 ± .4	1.2 ± .7	1.3 ± .6	.138
Protein/energy	23.8 ± 7.8	24.0 ± 4.4	26.2 ± 8.8	.650

CHO = carbohydrate, g = gram, HVT = high-volume training, kcal = kilocalories, LVT = low-volume training, MVT = moderate-volume training.

The main finding of this study was that significant, large-effect improvements were found in all groups for all variables except fat-free mass. While the greatest improvement was detected in the MVT group, the lowest improvement was observed in the LVT group.

As seen in Table 2, a significant difference was found between the first and last test measurements of weight, BMI, fat (%) and fat mass (kg) of the participants (P ≤ .05). No difference was found between the first and last test measurements of fat free mass (kg; P = .12). No difference was found between the groups in weight (P = .418), BMI (P = .57), fat (%) (P = .778), fat mass (P = .481) and fat free mass (kg; P = .472). When the effect size (ES) of η_p² was examined within groups, a small effect was observed in the fat free mass (kg) values of the participants in the LVT group (ES = 0.001, small ES), while the largest ES was observed in the fat (%) values (ES = 0.293, large ES; Table 2). In addition, the interaction effect (group × time) was significant in weight (kg), BMI (kg/m²), and Fat (%) measurements (Table 2).

Table 2.

Evaluation of change and percentage values of body composition measurements baseline and after training (N = 39).

	Pre	Post	Δ	%		F statistic
Variable	M ± SD	M ± SD	TB–Tend	TB–Tend	ηp2	Group X time	Time	Group
Body mass (kg)
LVT	54.8 ± 1.7	53.5 ± 1.4	−1.3 ± 0.9	0.9	0.082	0.001*	0.001*	0.418
MVT	53.8 ± 1.7	48.7 ± 1.4	−5.1 ± 1.4	10.4	0.598
HVT	55.1 ± 1.7	51.1 ± 1.4	−4.0 ± 4.0	7.8	0.481
BMI (kg/m2)
LVT	19.8 ± 1.7	19.5 ± 1.7	−0.3 ± 0.5	1.5	0.04	0.001*	0.001*	0.57
MVT	19.8 ± 1.9	17.9 ± 1.8	−1.9 ± 0.5	10.6	0.59
HVT	20.7 ± 2.8	19.3 ± 2.5	−2.3 ± 1.5	7.3	0.681
Fat (%)
LVT	21.9 ± 6.5	20.5 ± 5.9	−1.4 ± 1.3	6.8	0.293	0.001*	0.001*	0.778
MVT	23.8 ± 4.1	20.3 ± 3.4	−3.5 ± 1.4	17.4	0.733
HVT	23.7 ± 6.3	21.8 ± 6.2	−1.9 ± 1.1	8.7	0.438
Fat free mass (kg)
LVT	12.3 ± 4.7	11.6 ± 4.5	0.2 ± 1.3	6.1	0.001	0.113	0.12	0.472
MVT	12.0 ± 3.5	10.0 ± 2.7	−2.0 ± 1.9	19.9	0.157
HVT	16.9 ± 11.5	14.3 ± 6.6	−1.7 ± 4.2	17.9	0.438
Fat mass (kg)
LVT	42.4 ± 2.3	40.5 ± 2.1	−1.9 ± 1.2	4.7	0.254	0.052	0.001*	0.481
MVT	41.8 ± 3.6	38.0 ± 2.2	−3.8 ± 1.6	9.9	0.568
HVT	42.3 ± 5.4	38.9 ± 3.6	−3.4 ± 2.8	8.7	0.516

Δ = change, η_p² = partial eta squared, BMI = body mass index, HVT= high volume training, LVT= low volume training, M = mean, MVT = moderate volume training, post= post-intervention, pre = pre-intervention, SD = standard deviation.

^*P < .05.

There were time effects which indicated significant increases in vertical jump was observed in the MVT, (η_p² = 0.74) and HVT (η_p² = 0.69) groups and LVT group (0.009 There were significant time effects (P = .05) in PP values for LVT (η_p² = 0.100, moderate ES), MVT (η_p² = 0.047, small ES), and HVT (η_p² = 0.381, large ES). However, no significant differences were observed between group by time interaction in PP values between the trained groups (Table 3).

Table 3.

Evaluation of change and percentage values of vertical jump and peak power measurements baseline and after 8-week training period.

	Pre	Post	Δ	%	ηp2	F statistic
Variable	M ± SD	M ± SD	TB–Tend	TB–Tend		Group X time	Time	Main effect	Post hoc test
Vertical jump (cm)
LVT	17.5 ± 2.0	20.3 ± 1.7	2.7 ± 1.2	6.7	0.58	0.004*	0.009	0.001*	HVT = MVT > LVT
MVT	19.3 ± 1.7	23.2 ± 2.4	3.9 ± 1.5	18.2	0.74
HVT	19.7 ± 2.1	22.7 ± 1.9	3.5 ± 1.3	15.2	0.69
Peak power
LVT	1849 ± 23	2016 ± 33	166.6 ± 29	16.1	0.1	0.053	0.001*	0.216	–
MVT	1873 ± 30	2008 ± 36	331.1 ± 11	20.3	0.04
HVT	1915 ± 28	2308 ± 21	392.1 ± 26	18.6	0.38

Δ = change, η_p²= partial eta squared, HVT = high volume training, LVT = low volume training, M = mean, MVT = moderate volume training, post = post-intervention, pre = pre-intervention, SD = standard deviation.

^*P < .05.

When Table 4 was examined, the effects of group (P = .001) and time (P = .001) were statistically significant in the MT (cm) measurement results. Significant improvements were observed for LVT (η_p² = 0.368, small ES), MVT (η_p² = 0.829, large ES) and HVT (η_p² = 0.545, large ES). When the changes between the groups were examined, no difference was observed between the LVT and MVT groups. The LVT and MVT groups showed significant improvement compared to the HVT group and the highest improvement was found in the MVT group (Table 4).

Table 4.

Evaluation of change and percentage values of muscle thickness baseline and after 8-week training period.

n = 39	Pre	Post	Δ	%		F statistic
Variable	M ± SD	M ± SD	TB-Tend	TB-Tend	ηp2	Group X Time	Time	Group		Post hoc test
MT (cm)
LVT	1.9 ± 0.1	2.1 ± 0.1	0.13 ± .04	10.5	0.368	0.001*	0.001*	0.001*	LVT = MVT > HVT
MVT	2.0 ± 0.1	2.4 ± 0.1	0.37 ± 12	20	0.829
HVT	2.2 ± 0.2	2.4 ± 0.1	0.19 ± 13	9.1	0.545

Δ = change, η_p²= partial eta squared, HVT = high volume training, M = mean, MT = muscle thickness, LVT = low volume training, MVT = moderate volume training, post = post-intervention, pre = pre-intervention, SD = standard deviation.

^* P < .05.

As seen in Table 5, the group effect in RM (kg) results was statistically significant (P = .001). Increases were observed in total RM (kg) values in all groups. In total RM (kg), LVT increased by 23.4% (η_p² = 0.926, large ES), MVT by 43.2% (η_p² = 0.980, large ES), and HVT by 27.3% (η_p² = 0.951, large ES). The highest increase was found in the MVT group, while the lowest increase was found in the LVT group. In addition, time (P = .001) and interaction effect (P = .001) were also significant in 1RM (Table 5).

Table 5.

Evaluation of change and percentage values of fitness measurements baseline and after 8-week training period.

	Pre	Post	Δ	%	ηp2	F statistic
Variable	M ± SD	M ± SD	TB-Tend	TB-Tend		Group X Time	Time	Group	Post hoc test
BP (kg)
LVT	21.6 ± 4.9	27.9 ± 6.5	6.3 ± 3.4	29.1	0.619	0.001*	0.001*	0.010*	MVT > HVT = LVT
MVT	21.2 ± 1.9	36.6 ± 2.2	15.4 ± 1.9	72.3	0.917
HVT	25.4 ± 2.8	32.2 ± 3.6	6.8 ± 3.2	26.8	0.657
CP (kg)
LVT	24.5 ± 3.0	29.5 ± 3.0	5.0 ± 0.8	20.8	0.673	0.003*	0.001*	0.001*	LVT < MVT = HVT
MVT	23.9 ± 1.8	37.5 ± 1.8	13.6 ± 2.1	57.6	0.939
HVT	26.7 ± 3.5	33.0 ± 3.9	6.3 ± 2.8	24.3	0.766
SR (kg)
LVT	28.9 ± 4	36.9 ± 5.6	8.1 ± 2.5	27.9	0.558	0.001*	0.001*	0.104	–
MVT	28.1 ± 3.3	41.4 ± 5.1	13.3 ± 2.3	47.3	0.774
HVT	27.3 ± 4.8	34.2 ± 8.1	6.9 ± 6.6	25.3	0.481
LE (kg)
LVT	36.7 ± 3.7	42.5 ± 4.2	5.8 ± 2.5	15.9	0.287	0.003*	0.001*	0.003*	LVT < MVT = HVT
MVT	42.9 ± 3.6	56.5 ± 9.9	13.7 ± 8.3	31.6	0.692
HVT	39.9 ± 9.2	50.3 ± 10.6	10.3 ± 3.8	26.9	0.565
LC (kg)
LVT	41.7 ± 8.4	50.9 ± 8.9	9.2 ± 2.2	22.7	0.702	0.001*	0.001*	0.011*	MVT = HVT > LVT
MVT	47.5 ± 12.3	68.5 ± 10.1	21.1 ± 3.8	44.4	0.92
HVT	45.9 ± 8.2	59.9 ± 8.4	13.9 ± 4.3	31.8	0.84
LP (kg)
LVT	42.9 ± 6.6	53.1 ± 7.5	10.2 ± 3.3	20.6	0.49	<0.001*	0.095	0.002*	MVT > HVT = LVT
MVT	50.0 ± 7.5	64.5 ± 9.3	14.5 ± 9.6	30.5	0.66
HVT	46.5 ± 4.3	56.0 ± 5.0	9.5 ± 3.1	24.3	0.46
SQ (kg)
LVT	33.5 ± 5.9	42.5 ± 7.2	9.0 ± 2.6	27.3	0.83	0.001*	0.001*	0.707	–
MVT	32.7 ± 3.3	46.8 ± 3.4	14.1 ± 2.2	43.6	0.92
HVT	32.4 ± 6.0	45.2 ± 6.1	12.8 ± 2.2	40.9	0.91
RM total (kg)
LVT	229.7 ± 19.9	282.5 ± 19.9	53.5 ± 5.3	23.4	0.926	0.001*	0.001*	0.001*	MVT > HVT > LVT
MVT	246.1 ± 19.6	351.8 ± 23.6	105.7 ± 13.3	43.2	0.98
HVT	244.1 ± 15.9	310.7 ± 20.1	66.6 ± 6.4	27.3	0.951

1RMT = repetition maximum total weight, Δ = change, η_p² = partial eta squared, BP = bench press, CP = chest press, HVT = high volume training, M = mean, LC = leg curl, LE = leg extension, LP = leg press, LVT = low volume training, MVT = moderate volume training, pre = pre-intervention, post = post-intervention, RM = repetition maximum, SD = standard deviation, SR = seated row, SQ = squat.

^*P < .05.

5. Discussion

This study aimed to compare the effects of RT at different volumes of RT on muscle thickness and performance parameters in untrained women. The main finding of this study was that significant increases were observed in all groups, with the greatest improvements occurring in the MVT group. While the greatest improvements in muscle thickness, CMJ, and 1RM maximal strength were observed in the MVT group, the smallest improvements were observed in the LVT group. On the other hand, the LVT group experienced the greatest increase in PP values, while the HVT group exhibited the smallest gain in PP.

Schoenfeld et al^[48] found that progressively higher weekly training volumes resulted in greater muscle hypertrophy. In our study, the most notable improvement was observed in the MVT group. Similarly, another study revealed that customizing weekly training volume protocols resulted in greater increases in muscle cross-sectional area compared to standard group-based training.^[49] These findings align with the current study, emphasizing the importance of optimizing training volume for maximizing muscle hypertrophy. Starkey et al^[50] investigated the effects of a 14-week resistance exercise program with 2 different training volumes on muscle hypertrophy in untrained adults, reporting similar outcomes in torque output and muscle thickness across both groups. In contrast to their findings, our study revealed varying degrees of improvement in muscle thickness between the groups. In a study by Brigatto et al,^[51] a higher resistance training volume resulted in a greater increase in muscle hypertrophy. Additionally, a greater increase in lower-body muscle thickness (MT) and triceps brachii MT was observed in individuals training 32 sets per week compared to those performing 16 sets per week.^[51] However, in our study, the increase in the HVT group, which had the highest training volume, was less than that observed in the MVT group. These discrepancies between studies suggest that optimal volume training, rather than excessive volume, is more effective for promoting muscle hypertrophy. Similarly, a study on high-volume resistance training indicated that moderate volumes might be more beneficial compared to excessively high volumes, as excessive volume did not always translate to the greatest gains in fitness.^[52] Studies have shown that extended training durations of 4, 6, and 9 months lead to substantial increases in lean muscle mass and significant reductions in body fat percentage.^[53]

Our findings also showed that no significant change in body mass was observed in any of the groups after resistance training of different volume for 8 weeks yet the effect of time within the group was significant. According to 1 study, the most effective technique for reducing body fat (percentage) increases the volume of RT.^[54] Marx et al^[55] found that higher-volume exercise led to significant physiological adaptations associated with increased lean body mass and reduced body fat percentage. These findings contradict those of our study, where the MVT group demonstrated a greater reduction in body fat percentage (−3.5%) compared to the HVT group. Additionally, high-intensity, circuit-type integrated neuromuscular training has been shown to effectively impact energy balance and reduce both body mass and fat, indicating that moderate to high training volumes may provide considerable benefits for body composition.^[56]

In 1 study, all RT volumes increased bench press and squat 1RM strength. According to our findings, significant increases in the 1RM values were observed in the entire RT group. The largest increase was observed in the MVT group. In a study by Brigatto et al, ^[51] the group that trained 32 sets per week per muscle group had a greater 1RM increase in the lower body than those who trained 16 sets per week per muscle group. According to a meta-analysis, muscle strength development was superior for both high- and medium-load RT compared to low-load RT, and a nonsignificant but superior effect was found for high-load RT compared to medium-load RT.^[57] However, this study showed a greater improvement was observed in the MVT group. These differences may be related to the other training elements. In fact, many parameters, such as rest time between sets, average age of the participants, and sex or strength training experience, can affect muscle hypertrophy. The 1RM maximum strength for bench press, free weights, shoulder press, and leg press increased significantly after 4, 6, and 9 months of training in the periodic training group, whereas the single-set circuit group increased after only 4 months of training.^[53] In another study, the high-volume multiple-set group showed increases in upper and lower body maximum strength, muscle strength and speed, and high-intensity local muscle endurance compared to the single-set circuit training group.^[55]

In a study by Kraemer et al^[53], 3 different training protocols were applied: a no-resistance exercise control group, a periodized multiple-set resistance training group, and a single-set circuit resistance training group. Notably, in the periodized training group, a significant increase in power output was observed following 9 months of training.^[53] In a study by Marx et al,^[55] increases in upper and lower body muscle strength and speed were observed when the high-volume multiple-set group was compared with the single-set circuit training group. However, in our study, the highest increase in the peak power was observed in the LVT group. This may be because the participants in our study were untrained.

We would like to acknowledge that this study had some limitation that should be considered. First, the participant psychological factors such as self-motivation and interest in the program was not considered. Future study should assess the baseline psychological status of the participant to prevent any baseline bias. The second key limitation of this study is the absence of a control group. The lack of a control group limits the ability to fully understand the effects of the training intervention, as it prevents direct comparisons between those who received the intervention and those who did not. Including a control group could have enhanced the findings and contributed valuable knowledge to the understanding of dose-related effects of resistance training. Future research should aim to incorporate a control group to strengthen the conclusions drawn from such studies. Third, a portable ultrasound scanner was shown to have variability in measurement reliability. A portable ultrasound scanner has been previously used and demonstrated as an indirect method to measure muscle thickness. While it offers convenience and noninvasiveness, there are some limitations associated with this technique that should be acknowledged. These include potential variability in measurements due to operator skill, the influence of subcutaneous fat on accuracy, and the challenge of standardizing probe placement. To enhance the robustness of future assessments, it is advisable to consider incorporating more rigorous and standardized methods of muscle thickness measurement.

6. Conclusion

The findings of this study showed that all groups demonstrated improvements in all body composition measurements, except for fat-free mass, with no significant differences between the groups. All groups showed enhancements in vertical jump performance, with the high- and moderate-volume groups achieving higher increases compared to the low-volume group. No significant improvements in peak power were observed in any group. Muscle thickness increased across all groups, with the low- and moderate-volume groups showing greater improvements compared to the high-volume group. Fitness metrics improved in all groups, with the high- and moderate-volume groups exhibiting more significant gains in chest press, leg extension, and leg curl exercises. Additionally, the moderate-volume group demonstrated the greatest improvements in bench press, leg press, and 1RM total. No significant differences between groups were observed in the seated row and squat exercises. This study found that moderate-volume group demonstrating the most favorable adaptations in most cases. Effective exercise prescription requires a balance between undertraining and overtraining, and in this study, the moderate-volume group appeared to achieve that balance. These results offer valuable insights for designing long-term training programs for individuals without prior weight training experience. Future research should explore the effects of different weekly training volumes in diverse populations, including athletes, the elderly, individuals with sarcopenia, obese individuals, and postmenopausal women.

The study emphasizes the importance of optimizing training volume to maximize physical adaptations and performance improvements. Future investigations should continue to examine the impact of varying training volumes across different demographic groups to establish specific recommendations. Clinically, these findings highlight the need for individualized exercise programs that balance intensity and volume, particularly for those new to resistance training. Personalized training programs tailored to individual goals and capabilities can improve long-term adherence, enhance effectiveness, and ultimately support better health outcomes and physical performance.

Acknowledgments

We would like to thank Princess Nourah bint Abdulrahman University for supporting this project through Princess Nourah bint Abdulrahman University Researchers Supporting Project number (PNURSP2024R 286), Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia.

Author contributions

Conceptualization: Dondu Ugurlu, Mehmet Gülü.

Data curation: Dondu Ugurlu, Mehmet Gülü, Hakan Yapici.

Formal analysis: Mehmet Gülü, Hakan Yapici.

Funding acquisition: Monira I. Aldhahi.

Methodology: Mehmet Gülü, Monira I. Aldhahi.

Writing – original draft: Dondu Ugurlu, Mehmet Gülü, Hakan Yapici, Fatma Hilal Yagin, Ertan Comertpay, Oguz Eroglu, José Afonso, Monira I. Aldhahi.

Writing – review & editing: Dondu Ugurlu, Mehmet Gülü, Hakan Yapici, Fatma Hilal Yagin, Ertan Comertpay, Oguz Eroglu, José Afonso, Monira I. Aldhahi.