Impact of strength training of large muscle groups on quality of life

Abstract

Muscle-strengthening activities reduce the risk of various diseases and promote overall health. Physical activities targeting large muscle groups, such as weightlifting or resistance exercises, provide an additional health benefit. The present study investigated the relationship between strength training and health-related quality of life (HRQOL) through a cross-sectional study of 50 adults participating in large muscle group strengthening activities (LMG) and 50 adults who did not (NLMG). HRQOL was assessed using the SF-12v2 questionnaire, and sleep habits were assessed using the PSQI questionnaire. The LMG group had a significantly higher Role/Social component summary (RCS) score than the NLMG group (50.5 ± 7.2 vs 47.2 ± 8.3; respectively, p = 0.040). The physical component summary (PCS) and mental component summary (MCS) scores also tended to be higher in the LMG group than in the NLMG group (52.6 ± 8.4 vs 49.9 ± 10.2, respectively; p = 0.15 and 59.0 ± 7.9 vs 56.7 ± 6.0, respectively; p = 0.10). Linear regression analysis showed that a higher RCS score was significantly associated with LMG training, whereas higher PCS and MCS scores were associated with better sleep quality. These results suggest that strength training targeting large muscle groups may improve the social aspect of HRQOL, highlighting the potential benefits of incorporating such exercises into regular physical activity regimens.

Introduction

It is accepted that physical activity is beneficial to health. Muscle-strengthening activities reduce the risk of all-cause mortality, cardiovascular disease, total cancer, and diabetes mellitus by 10–17%.⁽¹⁾ In addition to morbidity and premature mortality, physical inactivity is responsible for a substantial economic burden.⁽²⁾ To maintain overall well-being, healthy adults should undertake at least 150–300 ‍min of moderate-intensity or 75–150 ‍min per week of vigorous-intensity aerobic activity such as walking, jogging, cycling, or swimming per week.⁽³⁾ Activities such as weightlifting or resistance exercises targeting large muscle groups (i.e., chest, back, shoulders, legs, arms, and core muscles) provide an additional health benefit; however, this beneficial effect has not been quantified. Here, we compared the health-related quality of life (HRQOL) of healthy adults who engaged in, or did not engage in, large muscle group strengthening activities as part of their daily lives.

An investigation into the association between exercise and HRQOL is necessary to identify the effects of exercise on sleep quality.⁽⁴⁾ Since irregular and low-quality sleep impairs HRQOL, it may be that exercise improves HRQOL indirectly by enhancing sleep quality.⁽⁵⁾ Indeed, a randomized controlled trial has shown that muscle-strengthening exercise significantly improves subjective sleep quality.⁽⁶⁾

This study aimed to measure the impact of a large muscle group strengthening program on HRQOL. The results suggest that the RCS, which reflects how health issues affect an individual’s ability to fulfill their social roles and engage in social activities, was higher in the muscle-strengthening group than in the non-muscle-strengthening group. These data provide insight into how this type of exercise can improve HRQOL, which will help us to develop targeted interventions.

Materials and Methods

Study design and participants

In this cross-sectional study, participants were recruited in four institutions: Matsudo Sports Park, Kakinokidai Park Gymnasium, Wanagaya Sports Center, and a Keio University-affiliated facility (Shujikan), between July 2023 and September 2023. A total of 100 adults [50 engaged in large muscle group strengthening activities (the LMG group) and 50 did not (NLMG group)] were enrolled. Participants who stated that they habitually trained large muscle groups at home or in the gym (e.g., squats, bench presses, and deadlifts) were assigned to the LMG group, while those who did not were assigned to the NLMG group. All participants used a tablet device to complete a questionnaire asking about demographics, exercise habits, medical history, HRQOL, and sleep habits.

We used the Japanese MOS 12-Item Short-Form Health Survey ver. 2 (SF-12v2) to measure HRQOL; this is a common and well-established health-related HRQOL scale comprising a 12-item subset of the SF-36 scale.⁽⁷⁾ The SF-12v2 has been validated for reliability in several languages, including Japanese. The physical component summary (PCS), mental component summary (MCS), and role/social component summary (RCS) scores are calculated from the answers to the 12 items.⁽⁸⁾ A meta-analysis has shown that the paper-based and electronic versions of the SF-36 and SF-12 are equivalent across various disease populations and countries.⁽⁹⁾

Sleep quality was measured using the Pittsburgh Sleep Quality Index Japanese version (PSQI-J) as a scale to assess the degree of sleep disturbance.^(10–12) A systematic review and meta-analysis of randomized controlled trials showed that compared with control interventions, exercise improves sleep quality significantly in adults with a low PSQI [Mean difference: −2.19 (95% confidence interval, −2.96 to −1.41)].⁽¹³⁾

Outcome measures

The primary outcome measure was HRQOL, assessed by calculating the PCS, MCS, and RCS scores based on the answers to the SF-12v2 questionnaire.

Statistical analysis

Differences between groups were analyzed using Welch’s unpaired t test (continuous variables) and Pearson’s χ² test (categorical variables). Linear regression analysis was used to investigate the association between HRQOL, muscle-strengthening training, and potential confounding factors. A two-sided p value <0.05 was considered significant. All statistical analyses were performed using IBM SPSS Statistics version 28 (IBM Corp., Armonk, NY).

Ethical considerations

The study was approved by the Ethics Committee of the Keio University Faculty of Pharmacy (approval number 230711-1) and was conducted in accordance with the 1964 Declaration of Helsinki. All participants provided written informed consent.

Results

Participant characteristics

The characteristics of the 100 study participants are listed in Table 1. There was no significant difference between the groups in terms of mean age. The number of males in the LMG group was higher than that in the NLMG group. The proportion of participants engaging in aerobic exercise was higher in the NLMG group than in the LMG group (p = 0.003). This difference is thought to be because participants were recruited from among gym-goers. The LMG group undertook a significantly higher frequency of exercise (mean: 3.5 days/week) than the NLMG group (mean: 2.1 days/week, p = 0.006). Notably, sleep quality was significantly better in the LMG group than in the NLMG group (p = 0.00047).

Table 1.

Participant characteristics

		NLMG (n = 50)	LMG (n = 50)	p value
Age (years) [mean ± SD]		43 ± 19	38 ± 18	0.20a
Sex	Female	30 (60.0%)	12 (24.0%)	0.0005b
	Male	20 (40.0%)	38 (76.0%)
Duration of exercise (years) [mean ± SD]		6.3 ± 2.6	9.6 ± 9.0	0.65a
Aerobic exercise		43 (86.1%)	30 (60.0%)	0.003b
Frequency of exercise (times/week)				0.006b
	1–2	24 (48.0%)	10 (20.0%)
	3–4	21 (42.0%)	23 (46.0%)
	5	3 (6.0%)	11 (22.0%)
	6–7	2 (4.0%)	6 (12.0%)
Timing of exercise
	Before breakfast	3 (6.0%)	2 (4.0%)	0.65b
	In the morning	22 (44.0%)	15 (30.0%)	0.15b
	After lunch	6 (12.0%)	6 (12.0%)	1.0b
	Before dinner	18 (36.0%)	22 (44.0%)	0.41b
	After dinner	24 (48.0%)	28 (56.0%)	0.42b
	After 10pm	2 (4.0%)	2 (4.0%)	1.0b
Survey facility				0.11b
	Facility 1	12 (24.0%)	12 (24.0%)
	Facility 2	15 (30.0%)	10 (20.0%)
	Facility 3	16 (32.0%)	11 (22.0%)
	Facility 4	7 (14.0%)	17 (34.0%)
Past medical history
	Cancer	1 (2.0%)	0 (0.0%)	0.32b
	Diabetes mellitus	2 (4.0%)	2 (4.0%)	1.0b
	Cerebrovascular disease	0 (0.0%)	1 (2.0%)	0.32b
	Cardiovascular disease	3 (6.0%)	0 (0.0%)	0.079b
PSQI score [mean ± SD]		8.6 ± 11.8	4.5 ± 2.4	0.00047a

NLMG, non-large muscle group strengthening group; LMG, large muscle group strengthening group; facility 1, Matsudo; facility 2, Kakinokidai; facility 3, Wanagaya; facility 4, Shujikan; PSQI, Pittsburgh Sleep Quality Index. ^aWelch’s unpaired t test; ^bPearson’s χ² test.

HRQOL scores

The LMG group had a significantly higher RCS score than the NLMG group (LMG, 50.5 ± 7.2; NLMG, 47.2 ± 8.3; p = 0.04) (Fig. 1). The PCS scores (LMG, 52.6 ± 8.4; NLMG, 49.9 ± 10.2; p = 0.15) and MCS scores (LMG, 59.0 ± 7.9; NLMG, 56.7 ± 6.0; p = 0.10) also tended to be higher in the LMG group than in the NLMG group, although the difference was not significant.

Fig. 1.

Differences in HRQOL related to strength training of large muscle groups. P values between the NLMG and LMG groups were calculated by Welch’s unpaired t test. PCS, physical component summary; MCS, mental component summary; RCS, role/social component summary; NLMG, non-large muscle group strengthening group; LMG, large muscle group strengthening group.

Linear regression analysis

Univariable linear regression analysis revealed a significant association between LMG training and higher RCS scores (β = 0.21, p = 0.040; Table 2). Male sex and better sleep quality were associated with higher PCS scores, whereas a higher frequency of exercise (more than 3 times per week) and better sleep quality were associated with higher MCS scores. In this study population, aerobic exercise was not associated with HRQOL. Because better sleep quality was marginally associated with higher RCS scores (β = −0.17, p = 0.086), we conducted a multivariable linear regression analysis that included both LMG training and sleep quality, with stepwise variable selection. Only LMG training was associated with higher RCS scores. These data suggest that LMG strengthening training is an independent factor that explains higher RCS scores.

Table 2.

Univariable linear regression analysis to elucidate factors associated with HRQOL

	PCS [β, p value]	MCS [β, p value]	RCS [β, p value]
NLMG	Ref.	Ref.	Ref.
LMG	0.15, 0.15	0.17, 0.10	0.21, 0.040
Sex
Female	Ref.	Ref.	Ref.
Male	−0.21, 0.033	−0.065, 0.52	0.055, 0.59
Aerobic exercise	−0.017, 0.87	−0.067, 0.51	0.014, 0.99
Frequency of exercise (times/week)
1–2	Ref.	Ref.	Ref.
3–4	0.0038, 0.97	0.23, 0.044	0.15, 0.19
5	0.083, 0.46	0.27, 0.015	0.016, 0.88
6–7	0.045, 0.68	0.23, 0.029	0.13, 0.21
PSQI score	−0.36, 0.00027	−0.36, 0.00021	−0.17, 0.086

PCS, physical component summary; MCS, mental component summary; RCS, role/social component summary; β, standardization coefficient; CI, confidence interval; NLMG, non-large muscle group strengthening group; LMG, large muscle group strengthening group; PSQI, Pittsburgh Sleep Quality Index. Values in bold are statistically significant.

Discussion

This study highlights that social HRQOL scores (particularly the RCS) were significantly higher in the LMG group than in the NLMG group; however, there were no significant differences between the groups concerning physical HRQOL scores (i.e., PCS) or mental HRQOL scores (i.e., MCS). Muscle-strengthening activities may enhance social well-being by increasing self-confidence, improving communication, and promoting the release of neurotransmitters such as dopamine, which can boost sociability. Physical exercise alters brain physiology and structure, thereby promoting cognitive improvement. Most of these effects are mediated by neurotrophins, increased adult hippocampal neurogenesis, attenuation of neuroinflammation, modulation of cerebral blood flow, and structural reorganization, in addition to promoting social interaction, all of which result in beneficial cognitive outcomes.⁽¹⁴⁾ The synthesis of nitric oxide (NO) and the secretion of testosterone, enhanced by exercise, may also contribute to the modulation of cerebral blood flow.^(15–18) However, previous studies did not compare the beneficial effects of aerobic and muscle-strengthening exercises on social health. The results of our study suggest that muscle-strengthening exercises improve the social health of those who undertake such training.

Physical activity has a positive impact on brain volume, particularly in the frontal and temporal regions, including the hippocampus. Increased physical activity is associated with greater brain volume and improved executive function in the frontal regions. Similarly, higher physical activity levels are correlated with increased hippocampal volume and improved spatial memory.⁽¹⁹⁾ In addition, sociability plays a crucial role in brain health; indeed, it is associated with increased brain volume and improved executive function, likely due to increased expression of stress hormones such as cortisol and monoamine neurotransmitters such as serotonin and dopamine. Differences in gene expression patterns are also implicated in this relationship.^(20,21) Since social isolation and low social engagement are associated with an increased risk of cognitive disorders, muscle-strengthening training is particularly recommended for individuals who live alone.⁽²²⁾

While this study provides valuable insight, its cross-sectional design limits the ability to establish causal relationships. In addition, because muscle mass was not measured in this study, it is unclear whether the increase in muscle mass by LMG training affects social HRQOL. Prospective cohort studies are needed to examine the relationship between LMG strengthening and HRQOL in more detail. Tracking changes over time would help elucidate causality, enable generalization and reproducibility, reduce selection bias, and collect additional data regarding exercise exposure and outcomes.

In conclusion, our data suggest that strength training programs targeting large muscle groups have a positive impact on the social aspects of HRQOL. Promoting these activities could enhance social participation among older adults and prevent lifestyle-related diseases, thereby contributing to improved overall health.

Author Contributions

TT and JM designed the study. TT collected the data. TE and TT analyzed the data. JM, TE, and YS wrote the original draft. All authors reviewed and edited the manuscript.

Funding

The authors received no specific funding for this work.

Conflict of Interest

No potential conflicts of interest were disclosed.