Comparison of the effects of 6-week progressive bodyweight and barbell-back squat programs on lower limb muscle strength, muscle thickness, and body fat percentage among sedentary young women

doi:10.21203/rs.3.rs-2196193/v1

The study aimed to compare the effects of the progressive bodyweight and barbell-back squat training program (60–80% 1RM) on muscle strength, muscle thickness, and body fat percentage in sedentary young women. Thirteen sedentary young women (19.77 ± 0.83 years) were randomly divided into the progressive bodyweight (n = 6) or barbell squat (n = 7) group. Each program consisted of 2 weekly training sessions for 6 weeks. Muscle strength (isokinetic knee extensor and flexor muscle peak torque of each leg), muscle thickness (gluteus maximus, rectus femoris, and gastrocnemius muscles), along with body fat percentage were measured objectively at baseline and post-testing. For the muscle strength, both groups showed a significant increase in isometric peak torque of the knee extensor and flexor (p < 0.05). However, there were no significant be-tween-group differences in isometric peak torque of the knee extensor and flexor (p > 0.05), as well as the mean concentric peak torque of the knee H/Q ratio (p > 0.05). For the muscle thickness, significant increases were also found within the two groups (p < 0.05) and without significant differences between the two groups (p > 0.05). The percentage of body fat significantly improved in the barbell (pre. 28.66 ± 4.58%. vs post. 24.96 ± 5.91%, p = 0.044), but not in the bodyweight group (pre. 24.18 ± 4.63% vs post. 24.02 ± 4.48%, p = 0.679). Although all of the groups increased maximum strength and muscle mass, our results suggest that the barbell back squat training may optimize the gains for decreasing the body fat percentage.

Health sciences/Health care/Public health

Health sciences/Anatomy/Musculoskeletal system

bodyweight squat variation

isokinetic peak torque

resistance training

lower limb

The squat exercise is a kind of multiple-joint exercise mainly to increase the strength and size of lower body muscles that descent and ascent the body center of gravity by flexing and extending the hip, knee and ankle (1). In recent decades, both the bodyweight and barbell-back squat are widely used to train lower limb muscle strength in variation populations. These two types of training have been gradually involved in progressive resistance training, in which participants exercise their muscles against bodyweight or barbell load resistance by progressively increasing the intensity as their strength improves (2, 3, 4).

As for the barbell-back squat training, a large number of relevant studies have consistently confirmed the training principles to achieve the improvement of low limb muscle strength, by controlling the increase of training load (percentage of 1RM) in each set, while the repetition times reduced accordingly. This resistance training principle was recognized as the repetition continuum, which was originated from the pioneering work of Delorme (5). For example, in order to promote the maximum strength, the training load and volume of the barbell-back squat were suggested at 85% or higher of 1RM of 2–6 sets, and the number of repetitions should be less than or equal to 6 times in a set (6). To promote both strength and hypertrophy of the lower limb, the training load should be maintained between 67% − 85% of 1RM of 3–6 sets, and the number of repetitions was recommended to be ranged from 6–12 times in a set (7). However, considering the inconvenience of accessing fitness equipment and professional guidance in China, and the kinematic differences between athletes and beginners, it may be difficult for female novices to keep the consistency of movements and postures with the increasing of load and intensity in barbell-back squat practice (8, 9). In addition, previous studies have shown that barbell back squat may increase the risk of injuries associated with excessive mechanical stress on the knee and lumbar intervertebral disk (10, 11). Accordingly, the development of effective progressive bodyweight program targeted for sedentary female novices attracted more and more attention.

Similar to the barbell-back squat training, increasing repetitions, shortening the rest-interval time, changing the squat angle, or increasing the difficulty of movement under constant load (weight) has also been widely applied to promote low limbs muscle during the bodyweight-squat training (12, 13, 14, 15). But previous studies showed that increases in repetitions or shortening the rest-interval time might lead to greater improvement in endurance rather than maximum strength (12, 13, 14, 15). This might be explained by that this kind of body-weight training program is contrary to the current progressive resistance training principle (pyramid training based on maximum repetitions) for enhancing muscle strength (2). Although some research demonstrated that increasing the difficulty of movement (i.e., changing the posture) instead of numbers of repetitions could achieve a higher training load and effectively improve the maximum strength, these researchers were interested in the upper limb (16). For example, Christopher et al. found that the progressive push-up variations from wall push-up to one-arm push-up showed similar effects on 1RM (one-maximum repetition) and muscle thickness of upper limb muscles compared with the bench press alone.

Moreover, effects of different squat postures have been proved to be different on muscle activation, but the majority of previous studies have focused on the single or comparison of several types of bodyweight squat (16, 17, 18, 19). In this respect, Lee et al. found in electromyography (EMG) analysis that the Spanish squat has greater activation of rectus femoris, vastus lateralis than the general bodyweight double-leg squat and wall squat (16). Also, different decline angles during a single-leg squat also involve different knee-muscle activity and muscle moments. Knoll et al. found different muscle activation using EMG between traditional Split Squats and single leg squat variation due to shifting body center, where the traditional Split Squats had more activation of quadriceps muscles, while single leg squat variation (single leg forward leaning squat) had more activation of gluteus maximus (17). Furthermore, in the study by Muyor et al., all participants were loaded with barbells of 5RM, but the results showed that the Monopodial Squat had higher EMG activity in the gluteus Medius, gluteus maximus, biceps femoris, vastus lateralis, and vastus medialis than Lateral Step-Up and split squat. Therefore, the compelling evidence of experimental results demonstrated that different squat variations have different degrees of muscle activation on the lower limbs by changing the load on one or both legs and the range of motion of knee joint (18). These findings proved that compared with the progressive barbell-back squat, which increases the training load by increasing the barbell weight, changing the squat postures might be a way to progress the training load. However, it is unclear how different bodyweight squats combined to progressively increase the training load so as to affect maximum strength and thickness in lower limb, and whether it could be achieved same effects as the progressive barbell-back squat training. Additionally, bodyweight squat training may have its own advantages. Begalle (2012) found that the great quadriceps-to-hamstrings (Q:H) coactivation ratio of lower limbs was very significant during unilateral bodyweight squat. The better Q:H ratio could be helpful in knee stability and injury prevention (20). Therefore, an effective progressive bodyweight squat program suitable for exercising whenever and wherever possible for the general population may be more cost-effective and would be interesting in investigated.

In consequence, the present study aimed to address the aforementioned gap of knowledge. The present study aimed to examine and compare the effects of 6-week progressive barbell-back and bodyweight squat training programs on muscle strength, thickness, and body composition in sedentary young women, so as to designing effective training programs for females. It was hypothesized that the training effect of the bodyweight squat on lower limbs may not be different from that of the barbell-back squat.

Study design

Recently, PC has entered the literature about organizational behavior (1). Positive psychology as "the science of positive and constructive subjectivity, strong personality attributes, and positive institutions" proposes to enhance the richness of life and eliminate disorders that occur when life lacks meaning (2). Constructive organizational behavior emphasizes taking heed to employees' strengths as opposed to their flaws (3). Positive psychological aspects like optimism and hope, and strength and resilience promote the importance of human resources (e.g., persons' expertise and abilities) and social capital (e.g., persons' social networks) in businesses (4–6). PC, just like social and human capital, may be administered and managed; yet, despite conventional capital and physical assets, it can be acquired with a relatively modest expense (7). The research on psychological capital (7, 8) identifies and defines the four aspects of self-efficacy hope, resilience, and optimism. Self-efficacy relates to people's perceptions that they can perform a variety of actions to achieve their desired goals (9). An individual's self-efficacy is determined by his or her belief in growth and achievement (10). Self-efficacy alludes to an individual's beliefs regarding their perceived competence for attaining achievements and accomplishing goals. Hope also serves as a major factor that encourages people's drive, goal attainment, and compatibility (3, 11). In other terms, individuals who have high hope feel a sensation that they can discover some means to achieve the things they desire, which enables them to generate alternate paths to achieving their targets in the event that their initiative-based strategies are obstructed (1). Optimism generally entails an emotional and intellectual readiness for the notion that positive things are often more significant than undesirable things in life (12). Optimism depends on the way an individual perceives and anticipates the results of everyday experiences (3). Pessimists view similar occurrences as internal, global, and constant, whereas optimists interpret them as external, variable, and unique (13). Scholars also have recognized resilience as a mechanism or force that boosts one's tolerance for adversity and anxiety (3, 14). Resilience is a form of growth that allows people to keep striving by doing their utmost in the midst of setbacks, adversity, life's paradoxes, and even favorable occurrences, advancements, or increased responsibilities (10).

Subjects

In September 2019, thirteen young women (aged 19.77 ± 0.83 years) without previous resistance exercise experience were conveniently recruited at Beijing Normal University. To participate in this study, the women had to be aged between 18 and 30 years, be weight stable (a weight change of < 3% of body weight) for 6 months (BMI < 30), be inactive (< 150-min of moderate to vigorous physical activity per week), not take any nutritional supplements and be free of medical problems that could be excluded by the study protocol. Physical or mental health problems, such as cardiovascular disease, patellar injury, muscle injuries, orthopedic problems, motion-limiting osteoarthritis, fibromyalgia, and depression, were screened using a validated medical screening questionnaire (21, 22). Finally, thirteen young women completed the study (Fig. 1). Each participant was informed about the objectives of the study and the experimental procedures. After agreeing to participate, the volunteers read and signed informed consent forms. The testing and training sessions took place at the College of P.E. and Sports at the Beijing Normal University and the Institute of Sports Medicine at the Third Hospital of Peking University and followed the ethical guidelines of the Declaration of Helsinki for the study of humans. The studies involving human participants were reviewed and approved by Experiment of Sports and Health Promotion Research Center, College of P.E and Sports, Beijing Normal University of Ethics Committee. Written informed consent to participate in this study was provided by the all participants. Written informed consent was obtained from the individuals for the publication of any potentially identifiable images or data included in this article.

Procedures

Each session was 60-min and was separated by at least 48 hours, including 15-min warm-up activities (10 activities, 15-min) as the initial segment, 30-min squat exercises (6 sets of bodyweight or barbell-squat for each group) as the activity segment, and 15 minutes cool-down exercises (8 activities, 15-min) as the final segment. Both the warming and cool-down exercises were the same in the two experimental groups. All sixteen training sessions were conducted under the supervision of two experienced exercise instructors, and special attention was given to the consistency of the movement pace (23). The instructors were undergraduates majoring in physical education and training, with at least 3 years of resistance training experience. The same instructors controlled the velocity of the concentric phase and eccentric phase during each squat for 2-s through verbal cadence in each session (24). In addition, two assistants recorded videos of each session. After training, the same assistant evaluated the quality of squatting movement on the self-developed movement quality scale by watching the video.

Familiarization Session

For the first two weeks (Weeks 1–2), participants attended the gym for four familiarization sessions to become familiarized with the exercise equipment and protocol in their respective groups (e.g., key points of attention in each activity). In the first week, the participants in the barbell group received 6 sets each set 10 repetitions of barbell squats without disks. And the participants in the bodyweight squat group received 6 sets of bodyweight squats according to the progressive bodyweight training protocol. During this period, in order to ensure that each participant can understand the correct squat movement and effectively squat in the familiar stage, two instructors will guide the participants at any time during the training. In the second week, they were required to attend baseline assessments twice (intervals of 48-h) based on their groups to determine the participants’ starting level of bodyweight squat movement in the bodyweight group and the participants’ one-repetition maximum of the barbell squat in barbell squat group (4). After the baseline assessments, the lowest values (one repetitions maximum and initial squat level) of participants in the two groups were taken as the evaluation results and used to determine the load in formal intervention. The evaluation approach of bodyweight squat movement level is referred to as the assessment of progressive push-up level in research by Kotarsky (2018) (16). Forty-eight hours after two weeks of familiarization visits, another baseline assessment of height, weight, body fat, and muscle strength and thickness were conducted in the laboratory of the Beijing Normal University and the Third Hospital at Peking University. Evidence is strong to show that the two-week short-term training will not have a significant impact on the physiological indicators of subjects (25). From week 3 (weeks 3–8), all participants began the formal intervention in each experimental condition.

The Progressive Bodyweight Squat Program

The progressive bodyweight squat involved 10 levels of squats from A-J (See supplementary S1) (26). For each participant, the squat level was gradually increased over the 6-week period according to the following principles. In each training session, all participants were required to finish 6 sets of squats, including 4 sets at the initial level and 2 sets of squats at the two sequentially lower levels. Repetitions of squats decreased with sets. For example, at the beginning of training, participants performed the first set of 12 repetitions for double leg squat or 6 repetitions per side for single leg squat. The second set was 10 repetitions for double leg squat or 5 repetitions per side for single leg squat. And the remainder of the 4 sets performed 8 repetitions for double leg squat of 4 repetitions for single leg squat. The rest period of each set in bodyweight squat training designed is equal to the barbell back squat group, which is 2 minutes. And the specific number of repetitions per set was based on the quality of movement in participants' performance and the intensity of their perceptions. The intensity of each session progressed was measured by Ratings of perceived exertion (OMNI-Resistance Exercise Scale) which was accomplished independently by every participant after each training (27). And the repetitions of each set performed in 12 training sessions (6 weeks) were calculated as the total training volume.

By default, all participants began with level C for the first set during familiarization sessions. If they could correctly complete 10 repetitions for double leg squat on four sets at level C in two consecutive training sessions, they could advance to level D. Until in the single leg squat stage, participants performed 5 repetitions per side for single leg squat on four sets at level F in two consecutive training sessions, they could advance to level G. For example, participants who began with level C were required to perform six sets of bodyweight squats, including 12 repetitions for double leg squats at level A, 10 repetitions for double leg squats at level B, and four sets of double leg squat at level C (8 repetitions/set). In total, in an exercise session, they were required to complete the following: 12 (A) / 10 (B) / 8 (C) / 8 (C) / 8 (C) / 8 (C) / 8 (C). From First training session at formal intervention (week 3), they were required to gradually increase to 12 (E) / 10 (F) / 8 (G) / 8 (G) / 8 (G) / 8 (G), after the participants achieved 12 repetitions of E level, 10 repetitions of F level and 4 sets of 8 repetitions of G level in this session (each side 4 repetitions). They would try to finished 12 (E) / 10 (F) / 10 (G) / 10 (G) / 10 (G) / 10 (G) in next session (each side 5 repetitions). If they could perform 12 (E) / 10 (F) / 10 (G) / 10 (G) / 10 (G) / 10 (G) in two consecutive sessions, they could progress to level H. And participants began with 12 (F) / 10 (G) / 8 (H) / 8 (H) / 8 (H) / 8 (H) and followed the same pattern to progress throughout the 6-week training. When they could not complete 8 repetitions for double leg squats or 4 repetitions on each side for single leg squats at each level, the progression ended, and they began again at the previous level. Example was shown in the Table 1.

Table 1

Bodyweight squat progression
Subjects	First session		Second session		Third session		Fourth session
	level	R × S	level	R × S	level	R × S	level	R × S
1	E/F/G/G/G/G	12/10/8/8/8/8	E/F/G/G/G/G	12/10/10/10/10/8	E/F/G/G/G/G	12/10/10/10/10/10	E/F/G/G/G/G	12/10/10/10/10/10
2	E/F/G/G/G/G	12/10/8/8/8/8	E/F/G/G/G/G	12/10/10/10/8/8	E/F/G/G/G/G	12/10/10/10//10	E/F/G/G/G/G	12/10/10/10/10/10
3	E/F/G/G/G/G	12/10/8/8/8/8	E/F/G/G/G/G	12/10/10/10/10/8	E/F/G/G/G/G	12/10/10/10/10/10	E/F/G/G/G/G	12/10/10/10/10/10
4	E/F/G/G/G/G	12/10/8/8/8/8	E/F/G/G/G/G	12/10/10/10/10/8	E/F/G/G/G/G	12/10/10/10/10/10	E/F/G/G/G/G	12/10/10/10/10/10
5	E/F/G/G/G/G	12/10/8/8/8/8	E/F/G/G/G/G	12/10/10/10/10/8	E/F/G/G/G/G	12/10/10/10/10/10	E/F/G/G/G/G	12/10/10/10/10/10
6	E/F/G/G/G/G	12/10/8/8/8/8	E/F/G/G/G/G	12/10/10/8/8/8	E/F/G/G/G/G	12/10/10/10/10/10	E/F/G/G/G/G	12/10/10/10/10/10
Note: Repetitions × Sets = R × S

The Progressive Barbell-back Squat Program

In the familiarization session, exercises were performed under two trained instructors. All subjects attended two training sessions during the first week to familiarize themselves with the equipment and squat techniques under instruction and to ensure they understood the proper squat technique. The instructors used a barbell (20 kg) and weight plates with different loads to measure each participant’s one-repetition maximum (1RM) in the second week. Based on the multiple-repetitions testing procedure, participants were required to perform 5 sets of 5 repetitions of their maximum load of squats to estimate their one-repetition maximum (1RM). A jump box was placed behind participants to ensure that their hips and thighs were close to the box when they squatted correctly (thighs were parallel to the ground, and knees did not extend beyond the toes). The barbell squat movement adopts a high-bar back squat action (4). Participants were asked to descend until the thigh was parallel to the ground during squatting (by bending the knee and hip until the greater trochanter of the femur formed a horizontal line with the upper end of the patella, and the position of the thigh and hip parallel to the box and the ground was used as the visual cue) and then rise to the starting position after receiving verbal instruction from the instructors.

Before the test, participants became familiarized with the equipment and had the barbell-back squat technique critiqued and corrected during the first to second familiar sessions (week 1). The test was preceded by a warm-up set of 8 repetitions of barbell squats without the plate. Participants then performed sets at progressively increasing loads until failing to complete a valid repetition, judged by their inability to complete the full range of motion. Ideally, subjects failed within 3–5 repetitions during the last and heaviest set (4). Therefore, from the second set, each set involved 5 repetitions of squats and progressed by the addition of two plates (2.5 kg per plate) in the subsequent set until participants were unable to complete a set. There was a 2-min break between sets. The 1RM was then calculated according to the Epley formula: 1RM = w(1 + r/30), assuming repetitions > 1, where r represents the number of repetitions and w is the weight of the load.

After the familiarization, from the third week, each exercise session involved 6 sets of barbell-back squat, which was preceded by a warm-up set of 12 repetitions beginning at 60% of predicted 1RM, progressing to 10 repetitions of 70% of predicted 1RM in the second set and then to 8 repetitions of 80% of 1RM in the last four sets, and we encourage participants attempted to achieve 1 extra repetition in each of the four sets. The specific numbers of repetitions per set were based on the quality and intensity of participants’ performance and their perceived exertion. And the total training volume was calculated by repetitions x sets performed in 12 training sessions (6 weeks). A 2-min rest period between subsequent sets was allowed. For example, for the first formal intervention (session 1), the barbell weights for participant A were 10/12/14/14/14/14 (kg), and the repetitions under each weight were 12/10/8 + 1/8 + 1/8 + 1/8 + 1. If she could complete an extra repetition in each of the last four sets, i.e., 12/10/9/9/9/9, then she would progress to a set of 12/10/10/10/10/10 in the next training session. After she could be achieved 12/10/10/10/10/10 in two consecutive sessions. Subsequently, the progression involved the addition of 2.5 kg for each set. The weights were increased to 12.5/14.5/16.5/16.5/16.5/16.5 (kg), and the repetitions in each set were 12/10/8/8/8/8. All participants’ progression loads were determined according to the progressive resistance training for healthy adults (2) and take the content of the first to fourth sessions in six weeks shown in Table 2 as an example.

Table 2

Barbell back squat progression
Subjects	First session		Second session		Third session		Fourth session
	weight	R × S	weight	R × S	weight	R × S	weight	R × S
1	30/32/34/34/34/34	12/10/9/9/8/8	30/32/34/34/34/34	12/10/9/9/9/9	30/32/34/34/34/34	12/10/10/10/10/10	30/32/34/34/34/34	12/10/10/10/10/10
2	40/44/46/46/46/46	12/10/9/9/8/8	40/44/46/46/46/46	12/10/9/9/9/9	40/44/46/46/46/46	12/10/10/10/10/10	40/44/46/46/46/46	12/10/10/10/10/10
3	40/44/46/46/46/46	12/10/9/8/8/8	40/44/46/46/46/46	12/10/9/9/9/9	40/44/46/46/46/46	12/10/10/10/10/10	40/44/46/46/46/46	12/10/10/10/10/10
4	46/50/54/54/54/54	12/10/9/8/8/8	46/50/54/54/54/54	12/10/9/9/9/9	46/50/54/54/54/54	12/10/10/10/10/10	46/50/54/54/54/54	12/10/10/10/10/10
5	40/44/46/46/46/46	12/10/9/9/8/8	40/44/46/46/46/46	12/10/9/9/9/9	40/44/46/46/46/46	12/10/10/10/10/10	40/44/46/46/46/46	12/10/10/10/10/10
6	40/44/46/46/46/46	12/10/9/9/8/8	40/44/46/46/46/46	12/10/9/9/9/9	40/44/46/46/46/46	12/10/10/10/10/10	40/44/46/46/46/46	12/10/10/10/10/10
7	50/56/60/60/60/60	12/10/9/8/8/8	50/56/60/60/60/60	12/10/9/9/9/9	50/56/60/60/60/60	12/10/10/10/10/10	50/56/60/60/60/60	12/10/10/10/10/10
Note: Repetitions × Sets = R × S, weight unite (kilogram)

Measurements

Measurements occurred at baseline and 48-h after the last training session of formal intervention. All personnel involved with measurements were blinded to the treatment status of the participants.

Anthropometrics

Body height, weight, and body composition (body fat percentage, lean body mass, minerals, and body water) were measured via InBody 770 (InBody Co, Ltd, Seoul, Korea) before beginning the training program and again 24-h after the last exercise bout. All participants were required to wear light clothing and no shoes. The subjects stood barefoot on the test platform, with their feet touching the electrodes of the test platform and their hands holding the test handle until the machine successfully tested the body composition indicators of the subjects.

Strength Measurement

Isokinetic knee extensor and flexor muscle peak torque of each leg were concentrically and eccentrically assessed using a dynamometer (PHYSIOMED CON-TREX-MJ, Schnaittach, Germany). Before the test, subjects warmed up by riding a stationary bike at its easiest setting (PRO2 ® SPORT TOTAL BODY, Tulsa, USA) while seated, with the seat and pedals adjusted to ensure that subjects were positioned properly to produce efficient power, for 10-min. After 3-min of rest, participants were seated and secured to the dynamometer using torso and inactive thigh straps. Both legs were secured to the machine arm by two soft pads allowing comfortable knee movement. Testing consisted of five successful (constant maximal effort) eccentric and concentric knee flexion and extension trials. Concentric and eccentric peak torque was measured at an angular velocity of 60° per second between 0° and 90° of knee flexion. Trials were performed at 60°/s at self-determined maximum effort. Participants were given prior instructions for the tasks and two practice trials to familiarize themselves with the procedure. Verbal encouragement was given throughout each trial to ensure that subjects elicited maximal effort.

Muscle Thickness Measurement

Muscle thickness was measured using a B-mode ultrasound device (SONIMAGEHS1 musculoskeletal ultrasonic diagnostic system, Tokyo, Japan) at 3 anatomical sites: a. gluteus maximus (the first third between the posterior superior iliac spine and the greater trochanter of the femur); b. rectus femoris (a point two-thirds of the distance between the anterior-superior iliac spine and the superior tip of the patella on the anterior aspect of the thigh); and c. gastrocnemius muscles (30% proximal between the lateral malleolus of the fibula and the lateral condyle of the tibia) as described previously (28, 29, 30) (Fig. 2). All scanning procedures were conducted with the subjects lying or sitting in a relaxed position with the dominant leg’s hip and knee. A 2.0–5.0 MHz scanning head was placed on the skin perpendicular to the tissue interface. A water-based gel was used, and minimal pressure was placed on the probe to prevent compression of the muscle. The thickness of each muscle was measured as the maximum distance between the fascia layers on the B-mode image using the caliper function provided by the ultrasonography equipment. The same investigator made all the ultrasound measurements. For further analysis, all images were stored on a data storage device. All measurements were conducted by the same operator, and the ICCs were 0.720 for gastrocnemius muscles, 0.587 for the rectus femoris, and 0.876 for the gluteus maximus.

Covariates

To decrease the potential effect of other variables, we used a suite of questionnaires to measure daily physical activity (27), eating behavior, movement quality, training volume, and perceived exertion of exercise during the intervention. Ratings of perceived exertion (OMNI-Resistance Exercise Scale) were obtained for each exercise session, which is an intensity measurement method widely used in sports training in addition to heart rate (31). To ensure the consistency of the training intensity, the perceived leg exertion at the end of 3 sets and 6 sets, as well as the perceived whole-body exertion at the end of 6 sets were measured. The training volume (sets × repetitions) was calculated for all 12 training sessions (6 weeks). All participants were required to maintain their normal physical activity and eating habits, not to perform extra resistance exercises, and not to consume muscle supplements (such as protein powder). If there was a significant difference between groups in the abovementioned variables or if these variables were significantly related to the outcomes measured, they were controlled for as covariates in the analysis.

Statistical analysis

Normality assumptions were performed using the Kolmogorov–Smirnov test, and equal variance assumptions were performed using the Levene test (P < 0.05). For baseline comparisons between groups in age, weight, body fat, maximum strength, and muscle thickness, the independent-sample t-test was conducted if normality was assumed. If not, the Mann–Whitney U test was conducted. If normality and equal variance were assumed, changes in all outcomes were compared within the groups using a paired-sample t-test. If pre-test values were significantly different between groups at baseline, analysis of covariance (ANCOVA) was applied to test differences in post-test values between groups, including pretest values as a covariate; if not, the independent-sample t-test was conducted. SPSS version 26 (SPSS, Inc., Chicago, IL, USA) was used for the statistical analyses. The level of significance was set at p < 0.05. All values are presented as the mean ± standard deviation (SD).

Insert the text of the results here. Baseline descriptive characteristics of the participants who completed the study were reported in Table 3. At baseline, the two groups were well matched in terms of baseline age, height, weight, body fat, maximal strength, and muscle thickness (p>0.05). The total training volume (repetition х sets) between the two groups for 12 sessions was no significant difference (F=4.24, p=0.142), although the bodyweight squat group (713.67±7.09) was slightly higher than the barbell squat group (709.29±1.89). And there were also no significant differences between training intensity and motion quality during the intervention after 3 sets of perceived leg exertion (F=2.52, p=0.19), after 6 sets of perceived leg (F=0.16, p=0.87), after 6 sets of perceived whole-body exertion (F=0.09, p=0.31), and activity quality (F=2.38, p=0.58) (Figure 3).

Table 3. Baseline characteristics of participants (mean, standard deviation)

Group	bodyweight group (n=6)	barbell-back group (n=7)	F（P）
Age	19.25±0.50	20.50±1.00	0.23 (0.07)
Height (cm)	162.35±4.47	167.48±7.55	0.32 (0.29)
Weight (kg)	51.10±4.39	58.66±8.42	4.73 (0.08)
Body fat percentage (%)	24.18±4.63%	28.66±4.58%	0.06 (0.06)

Note: *independent-sample t-test, p≤0.05. Descriptive statistics for all study participants (mean ± SD).

Within-group differences in changes in maximum strength, muscle thickness, and body fat

After 6 weeks, the body fat percentage was significantly lower in the barbell-back squat group (t (7) =2.54, P<0.05) but not in the bodyweight squat group (t (6) =0.58, p=0.59). Same as the participants in the barbell-back squat group, the muscle thickness of the gastrocnemius (t (7) =-3.37, p<0.05) and gluteus maximus (t (7) =-7.26, p<0.001) was increased significantly in the bodyweight group (t (6) =-2.68, p<0.05), t (6) =-5.88, p<0.05). In both groups, the thickness of the rectus femoris did not change significantly (Barbell-back: t (7) =-1.79, p=0.12, Bodyweight: t (6) =-2.59, p=0.05) (Table 4).

Table 4. Effects on lower limbs muscle thickness

Items	bodyweight group			barbell-back group			Between
Muscle thickness (mm)	Pre	Post	P	Pre	Post	P	P
Gastrocnemius	14.20±1.49	16.20±2.14	0.04	16.13±2.93	18.73±2.40	0.02	0.82
Rectus femoris	14.73±2.14	17.00±1.52	0.05	17.36±3.14	19.46±3.27	0.12	0.54
Gluteus maximus	28.15±3.72	33.50±2.34	0.00	29.31±4.67	33.44±4.50	0.00	0.91

Note: Pre- and Post-*Paired Sample T-test, p≤0.05, Between Group-*independent-sample t-test, p≤0.05. Descriptive statistics for all study participants (mean ± SD).

In the barbell back squat group, changes in muscle strength were depicted in Figure 6 (Figure 4). For the right knee, the concentric peak torque of flexors (RCF) (t (7)=-4.30, p<0.05) and extensor (RCE) (t (7)=-2.60, p<0.05), as well as the eccentric peak torque of flexor (REF) (t (7)=-2.51, p<0.05) and extensor (REE) (t (7)=-0.89, p=0.41) were significantly increased. For the left knee, the concentric peak torque of the flexor (LCF) (t (7) =-3.65, p<0.05) and extensor (LCE) (t (7) =-3.27, p<0.05), as well as the eccentric peak torque of the flexor (LEF) (t (7) =-2.76, p<0.05) were significantly changed but not for the eccentric peak torque of extensor (LEE) (t (7) =-1.59, p=0.16). For the hamstring-to-quadriceps ratio (H/Q-ratio) of the knee, the mean concentric peak torque of the right knee H/Q-ratio (RCHQ) was t (7) =-1.22, p=0.27. The mean concentric peak torque of the left knee H/Q-ratio (LCHQ) was t (7) =-0.67, p=0.53 (Table 5).

Table 5. Effects of maximal strength, H/Q ratio and body fat in two types of progressive resistance training

Group	bodyweight squat			barbell-back squat				Between difference
Items	pre	post	P	pre		post	P	P
Isokinetic (Nm)	60°/sec	60°/sec		60°/sec	60°/sec
RCE	69.67±11.70	77.23±16.71	0.26	91.17±17.34	107.67±27.82		0.04	0.34
RCF	47.27±5.97	58.73±9.51	0.01	53.84±11.16	67.34±14.70		0.00	0.51
REE	99.40±26.36	123.37±30.40	0.01	144.70±29.28	154.49±37.04		0.41	0.83
REF	64.33±14.90	73.27±18.65	0.10	82.87±22.43	94.36±16.63		0.05	0.17
LCE	72.98±12.39	85.73±6.12	0.04	99.03±29.77	107.93±31.27		0.01	0.89
LCF	45.67±4.61	55.32±11.46	0.06	54.97±0.35	60.37±0.18		0.01	0.67
LEE	115.15±21.26	119.87±18.13	0.34	139.01±40.20	150.96±38.17		0.16	0.77
LEF	61.65±9.63	75.28±19.59	0.06	81.76±23.95	98.09±16.35		0.03	0.18
H/Q ratio (%)	60°/sec	60°/sec		60°/sec	60°/sec
RCHQ	72.52±15.80%	80.23±1.88%	0.32	66.51±10.12%	70.14±14.55%		0.27	0.25
LCHQ	68.25±15.13%	68.88±13.03%	0.93	57.43±8.50%	59.86±11.12%		0.53	0.51
Fat (%)
Body fat	24.18±4.63%	24.02±4.78%	0.68	28.66±4.58%	24.96±5.91%		0.04	0.55

Note: Pre- and Post-*Paired Sample T-test, p≤0.05, Between Group-*independent-sample t-test, p≤0.05. Descriptive statistics for all study participants (mean ± SD). Right Knee Concentric Peak Torque of Extensor = RCE, Right Knee Concentric Peak Torque of Flexor = RCF, Right Knee Eccentric Peak Torque of Extensor = REE, Right Knee Eccentric Peak Torque of Flexor = REF, Left Knee Concentric Peak Torque of Extensor = LCE, Left Knee Concentric Peak Torque of Flexor = LCF, Left Knee Eccentric Peak Torque of Extensor = LEE, Left Knee Eccentric Peak Torque of Flexor = LEF. The Mean Concentric Peak torque of Hamstring-to-Quadriceps Ratio in Right Knee = RCHQ, The Mean Concentric Peak Torque of Hamstring-to-Quadriceps Ratio in Left Knee = LCHQ

In the bodyweight squat group, with regard to the isokinetic torque of the right knee, changes for the concentric peak torque of the flexor (RCF) was t (6)=-3.73 (p<0.05), for the concentric peak torque of the extensor (RCE) was t (6)=-1.26 (p=0.26), for the eccentric peak torque of the flexor (REF) was t (6)=-2.03 (p=0.10), and for the eccentric peak torque of extensors (REE) was t (6)=-4.41 (p<0.05). For the left knee, the concentric peak torque of the flexor (LCF) was t (6) =-2.43 (p=0.06), the concentric peak torque of the extensor (LCE) was t (6) =-2.85 (p<0.05), the eccentric peak torque of the flexor (LEF) was t (6)=-2.44 (p=0.06), and the eccentric peak torque of the extensor (LEE) was t (6)=-1.06 (p=0.34). For the H/Q ratio, the mean concentric peak torque of the knee H/Q ratio (RCHQ) was t (6) =-1.11 (p=0.316). The mean concentric peak torque of the knee H/Q-ratio (LCHQ) was t (6) =-0.96 (p=0.93).

Between-group differences in changes in maximal strength, muscle thickness, and body fat

After 6 weeks, there were no significant differences in the peak torque of knee extensor and flexor, as well as the H/Q ratio between two groups (N·m) (p≥0.05, Table 6). No significant between-group differences were observed for the lower limb muscle thickness (Figure 5). The gastrocnemius thickness of the two groups was F=0.05 (p=0.84), the rectus femoris thickness was F=1.54 (p=0.28), and the gluteus maximus thickness was F=1.61 (p=0.27). As table 4 shown, there were also no significant differences between groups for the body weight (F=0.84, p=0.41) and body fat (F=0.44, p=0.55). For the change value of pre-and post-measurement, there were also no significant differences in the change value of isokinetic peak torque, H/Q ratio and body fat (Table 6).

Table 6. The D-value of isokinetic peak torque, H/Q ratio and body fat in two types of progressive resistance training

Group	bodyweight group (n=6)	barbell-back group (n=7)	P
Body fat percentage (%)	0.17±0.93%	3.7±3.85	0.022*
Rectus femoris (mm)	2.00±1.83	2.74±2.35	0.933
Gluteus maximus (mm)	2.27±2.14	2.1±3.11	0.440
Rectus femoris (mm)	5.35±2.23	4.13±1.51	0.261
Isokinetic (Nm)
RCE	7.57±14.72	16.93±17.21	0.693
RCF	11.47±7.54	10.64±6.99	0.630
REE	23.97±13.3	9.93±29.15	0.066
REF	8.98±10.84	11.49±12.12	0.952
LCE	12.75±10.96	8.90±7.21	0.342
LCF	9.65±9.71	5.40±3.91	0.294
LEE	4.72±10.94	11.94±19.91	0.366
LEF	14.17±13.04	16.33±15.68	0.471
H/Q ratio (%)
RCHQ	3.18±17.56%	6.06±5.56%	0.176
LCHQ	1.80±9.39%	1.31±15.72%	0.501

Note: D-value= post-test value-pre-test value, Pre and Post-*Paired Sample T-test, p≤0.05, Between Group-*independent-sample t-test, p≤0.05. Descriptive statistics for all study participants (mean ± SD).

Insert the text of the discussion here. The purpose of this study was to compare the effects of two different progressive squat programs (bodyweight and barbell-back squat) on body fat, as well as lower limb muscle thickness and strength in sedentary women. Although the training intensity and volume were consistent in the two groups, the main findings demonstrated similar increases in lower limb isokinetic peak torque and muscle thickness but different body fat change across the experimental groups.

Previous studies showed that bodyweight squat can progress and enhance training intensity by increasing repetitions (13). However, under such progressive strategy (increase repetitions under a fixed load), both untrained and trained people may not be very effective in improving the maximum strength (32, 33). This progressive strategy may be more effective for improving muscle endurance (9). The present study proved that the maximum strength and training intensity of the progressive bodyweight squat program could be promoted by decreasing the number of repetitions with increasing the difficulty of different body and leg postures.

Regarding muscle strength, both groups of untrained women exhibited comprehensive improvements, including in right knee concentric peak torque of flexor, right knee eccentric peak torque of extensor and left knee concentric peak torque of extensor. The results of this study were consistent with previous studies showing that more activation of lower limb muscles during the concentric phase when participants performed single-leg squats and lunge squats (34). Results about the bodyweight squat in this study were also consistent with those of previous studies, which showed that various leg squats can significantly stimulate the quadriceps and hamstrings (35, 36). The H/Q ratio is an important index for knee stability and rehabilitation. The H/Q ratio was maintained at a high level before and after training in the bodyweight squat group (68%-80%), which is comparable with a typical H/Q ratio of a healthy knee (50% and 80%) (35). These results demonstrated that bodyweight squat is a suitable approach to maintaining knee stability. The lower-limb symmetry of the H/Q ratio also did not significantly change after the bodyweight squat intervention, which is inconsistent with a previous study suggesting a significant difference in the H/Q ratio between the dominant and non-dominant legs in young women (37). The reason might be that many unilateral squats were involved in the bodyweight squat, which reduced the reliance on the dominant limb in training. It was one of the benefits of the unilateral bodyweight squat.

Muscle cross-sectional areas had a significant relationship with strength-velocity characteristics of the whole muscle and greater force production (38, 39). The muscle cross-sectional area of both groups showed similar significant improvements and did not significantly differ between groups. This finding was consistent with a previous study showing that muscle cross-sectional area has a positive relationship with maximal forces (38). In the present study, the cross-sectional area of the gluteus maximus increased to a greater extent than those of the rectus femoris and the gastrocnemius in the bodyweight squat group. In this case, the most common squat types were lunge and single-leg squat in bodyweight squat (18), which was consistent with the findings of a previous study that the gluteus maximus has more EMG activity than the rectus femoris and the gastrocnemius during the forward lunge and single-leg squat. In our cases, the muscle cross-sectional area of the gluteus maximus and gastrocnemius of the barbell-back squat were significantly improved. The muscle cross-sectional area of the rectus femoris showed no significant improvement. This may be related to the fact in the barbell squat training, participants were always required to control the knee joint not to exceed the toe too much since limiting the forward displacement of the knee will lead to more force transfer to the hip (10). And with the increase of load, the activation of the gluteus maximus is also proportional to it in the barbell squat (39). This may explain the greater improvement in the gluteus maximus muscle cross-sectional area of the barbell-back squat group than in the rectus femoris.

Finally, regarding the body fat, the participants in the barbell-back squat had a significantly decreased percentage of body fat without a change in body weight. This finding was consistent with a previous study showing that the body fat of untrained women decreases rapidly during the four weeks of resistance training (40). And the significant difference in the improvement may also be due to the relatively high body fat of subjects in the barbell group.

Practical Implications

Accordingly, the progressive bodyweight squat program developed could be widely applied for the general population. It is also valuable for therapists and practitioners with back problems to improve lower limb muscle strength without additional burden on the back, especially when back problems are always accompanied by reduced lower limbs muscle strength.

Limitations And Future Research

Nevertheless, our study has limitations that need to be addressed. First, although the subjects were strictly instructed to maintain their normal diet, the lack of diet control might be a confounding factor modulating muscle mass accretion. Second, it would be interesting to have longer training periods to investigate the long-term effect of the two training sessions on body fat, and muscle strength and thickness. Finally, and most importantly, the small sample size of participants involved in the intervention may be limited the generalizability of the results. The training effects of a larger sample need further study.

Data availability

The datasets analyzed during the current study are available from the corresponding author on reasonable request.

Author information

Authors and Affiliations

College of Physical Education and Sport, Beijing Normal University, Xinjiekouwai Street 19, Haidian District, Beijing, 100875, China

Wei Wei, WuL Zhang, Li He, Ronghai Su

The Sports Medicine Laboratory of Peking University Third Hospital, Peking University Health Science Center, Huayuan North Road 49, Haidian District, Beijing, 100191, China

JingX Zhu, Shuang Ren

Department of Kinesiology and Community Health, University of Illinois at Urbana-Champaign, Champaign 1206 South Fourth Ave Champaign, IL 61820, the United States.

YKuen Jan

Contributions

LH and WW conceived the and designed the study. WW and WLZ did the literature review. WW, JXZ, SR and RHS did the initial data collection and analysis. LH and RHS wrote the first draft of the manuscript. JXZ, SR, YKJ, WLZ, and LH critically edited the draft. All authors reviewed and had final approval of the submitted and published versions.

Corresponding author

Funding

This research was funded by a grant from National Natural Science Foundation of China Youth Science Foundation (81602869)

Ethics declarations

The studies involving human participants were reviewed and approved by Experiment of Sports and Health Promotion Research Center, College of P.E and Sports, Beijing Normal University of ethics committee. Written informed consent to participate in this study was provided by the all participants. Written informed consent was obtained from the individuals for the publication of any potentially identifiable images or data included in this article.

Conflict of Interest

The author(s) declare no competing interests.

Clark, D. R., Lambert, M. I., and Hunter, A. M. Muscle activation in the loaded free barbell squat: a brief review. J Strength Cond Res. 26, 1169–1178 (2012). https://doi.org/10.1519/JSC.0b013e31822d533d
American College of Sports Medicine. American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Med Sci Sports Exerc. 41, 687–708 (2009). https://doi.org/10.1249/MSS.0b013e3181915670
Aube, D., Wadhi, T., Rauch, J., Anand, A., Barakat, C., Pearson, J., Bradshaw, J., Zazzo, S., Ugrinowitsch, C., and De Souza, E. O. Progressive Resistance Training Volume: Effects on Muscle Thickness, Mass, and Strength Adaptations in Resistance-Trained Individuals. J Strength Cond Res. 36, 600–607 (2022). https://doi.org/10.1519/JSC.0000000000003524
Baechle, TR., Earle, RW., and Wathen, D. Resistance training. In: Essentials of Strength Training and Conditioning (3rd ed.), (Champaign, IL: Human Kinetics 2008),
COFFEY T. H. Delorme method of restoration of muscle power by heavy resistance exercises. Treat Serv Bull. 1, 8–11 (1946).
Fleck, SJ., and Kraemer, WJ. Designing Resistance Training Programs. 4th ed. (Champaign, IL: Human Kinetics 2014).
Garber, C. et al.. American College of Sports Medicine. American College of Sports Medicine position stand. Quantity and quality of exercise for developing and main-taining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Med Sci Sports Exerc. 43, 1334–1359 (2011). https://doi.org/10.1249/MSS.0b013e318213fefb
Li, X., Adrien, N., Baker, J. S., Mei, Q., and Gu, Y. Novice Female Exercisers Exhibited Different Biomechanical Loading Profiles during Full-Squat and Half-Squat Practice. Biology (Basel). 10, 1184 (2021). https://doi.org/10.3390/biology10111184.
Flores, V., Becker, J., Burkhardt, E., and Cotter, J. Knee Kinetics During Squats of Var-ying Loads and Depths in Recreationally Trained Women. J Strength Cond Res. 34, 1945–1952 (2020). https://doi.org/10.1519/JSC.0000000000002509.
Fry, A. C., Smith, J. C., and Schilling, B. K. Effect of knee position on hip and knee tor-ques during the barbell squat. J Strength Cond Res. 17, 629–633 (2003). https://doi.org/10.1519/1533-4287(2003)017<0629:eokpoh>2.0.co,2
Yanagisawa, O., Oshikawa, T., Adachi, G., Matsunaga, N., and Kaneoka, K. Acute effects of varying squat depths on lumbar intervertebral disks during high-load barbell back squat exercise. Scand J Med Sci Sports. 31, 350–357 (2021). https://doi.org/10.1111/sms.13850.
Hollingsworth, J. C., Young, K. C., Abdullah, S. F., Wadsworth, D. D., Abukhader, A., Elfen-bein, B., and Holley, Z. Protocol for Minute Calisthenics: a randomized controlled study of a daily, habit-based, bodyweight resistance training program. BMC public health. 20, 1242 (2020). https://doi.org/10.1186/s12889-020-09355-4
Tsourlou, T., Gerodimos, V., Kellis, E., Stavropoulos, N., and Kellis, S. The effects of a calisthenics and a light strength training program on lower limb muscle strength and body composition in mature women. J Strength Cond Res. 17, 590–598 (2003). https://doi.org/10.1519/1533-4287(2003)017<0590:teoaca>2.0.co,2.
Thomas, E., Antonino B., Mancuso, E., and Patti A. The effects of a calisthenics training intervention on posture, strength and body composition. Isokinet Exerc Sci. 25, 215-222 (2017). doi: https://doi.org/10.3233/IES-170001
Kotarsky, C. J., Christensen, B. K., Miller, J. S., and Hackney, K. J. Effect of Progressive Calisthenic Push-up Training on Muscle Strength and Thickness. J Strength Cond Res. 32, 651–659 (2018). https://doi.org/10.1519/JSC.0000000000002345
Lee, J. H., Kim, S., Heo, J., Park, D. H., and Chang, E. Differences in the muscle activities of the quadriceps femoris and hamstrings while performing various squat exercises. BMC Sports Sci Med Rehabil. 14, 12 (2022). https://doi.org/10.1186/s13102-022-00404-6
Knoll, M. G., Davidge, M., Wraspir, C., and Korak, J. A. Comparisons of Single Leg Squat Variations on Lower Limb Muscle Activation and Center of Pressure Alterations. Int J Exerc Sci. 12, 950–959 (2019).
Muyor, J. M., Martín-Fuentes, I., Rodríguez-Ridao, D., and Antequera-Vique, J. A. Electromyographic activity in the gluteus medius, gluteus maximus, biceps femoris, vastus lateralis, vastus medialis and rectus femoris during the Monopodal Squat, Forward Lunge and Lateral Step-Up exercises. PloS one. 15, e0230841 (2020). https://doi.org/10.1371/journal.pone.0230841
Glave, A. P., Olson, J. M., Applegate, D. K., and Brezzo, R. D. The effects of two different arm positions and weight status on select kinematic variables during the bodyweight squat. J Strength Cond Res. 26, 3148–3154 (2012). https://doi.org/10.1519/JSC.0b013e318243fefb
Begalle, R. L., Distefano, L. J., Blackburn, T., and Padua, D. A. Quadriceps and ham-strings coactivation during common therapeutic exercises. J Athl Train. 47, 396–405 (2012). https://doi.org/10.4085/1062-6050-47.4.01
Hu, B. et al.. Reliability and relative validity of three physical activity ques-tionnaires in Taizhou population of China: the Taizhou Longitudinal Study. Public Health. 129, 1211–1217 (2015). https://doi.org/10.1016/j.puhe.2015.03.024.
Wanner, M., Probst-Hensch, N., Kriemler, S., Meier, F., Bauman, A., and Martin, B. W. What physical activity surveillance needs: validity of a single-item questionnaire. Br J Sports Med. 48, 1570–1576 (2014). https://doi.org/10.1136/bjsports-2012-092122.
Almonroeder, T. G., Watkins, E., and Widenhoefer, T. Verbal Instruction Reduces Pa-tellofemoral Joint Loading During Bodyweight Squatting. J Sport Rehabil. 29(4), 463–468 (2019). https://doi.org/10.1123/jsr.2018-0157.
Morrissey, M. C., Harman, E. A., Frykman, P. N., and Han, K. H. Early phase differential effects of slow and fast barbell squat training. Am J Sports Med. 26, 221–230 (1998). https://doi.org/10.1177/03635465980260021101
Vrbik, I. et al.. The Influence of Familiarization on Physical Fitness Test Results in Primary School-Aged Children. Pediatr Exerc Sci. 29, 278–284 (2017). https://doi.org/10.1123/pes.2016-0091
Wade, P. Convict Conditioning: How to Bust Free of All Weakness Using the Lost Secrets of Supreme Survival (1st ed.). Little Canada, MN: (Dragon Door Publications 2012).
Craig, C. L. et al.. International physical activity ques-tionnaire: 12-country reliability and validity. Med Sci Sports Exerc. 35, 1381–1395 (2003). https://doi.org/10.1249/01.MSS.0000078924.61453.FB
Tillquist, M. et al.. Bedside ultrasound is a practical and reliable measurement tool for assessing quadriceps muscle layer thickness. JPEN J Parenter Enteral Nutr. 38, 886–890 (2014). https://doi.org/10.1177/0148607113501327.
Turton, P., Hay, R., and Welters, I. Assessment of peripheral muscle thickness and ar-chitecture in healthy volunteers using hand-held ultrasound devices, a comparison study with standard ultrasound. BMC medical imaging. 19, 69 (2019). https://doi.org/10.1186/s12880-019-0373-x.
Nunes, G. S., Barton, C. J., and Serrão, F. V. Hip rate of force development and strength are impaired in females with patellofemoral pain without signs of altered gluteus medius and maximus morphology. J Sci Med Sport. 21, 123–128 (2018). https://doi.org/10.1016/j.jsams.2017.05.014
Lea, J., O'Driscoll, J. M., Hulbert, S., Scales, J., and Wiles, J. D. Convergent Validity of Ratings of Perceived Exertion During Resistance Exercise in Healthy Participants: A System-atic Review and Meta-Analysis. Sports Med Open. 8, 2 (2022). https://doi.org/10.1186/s40798-021-00386-8
Jenkins, N. D. et al.. Neuromuscular Adaptations After 2 and 4 Weeks of 80% Versus 30% 1 Repetition Maximum Resistance Training to Failure. J Strength Cond Res. 30, 2174–2185 (2016). https://doi.org/10.1519/JSC.0000000000001308
Vann, C. G. et al.. Effects of High-Volume Versus High-Load Resistance Training on Skeletal Muscle Growth and Molecular Adaptations. Front Physiol. 13, 857555 (2022). https://doi.org/10.3389/fphys.2022.857555.
Muyor, J. M., Martín-Fuentes, I., Rodríguez-Ridao, D., and Antequera-Vique, J. A. Electromyographic activity in the gluteus medius, gluteus maximus, biceps femoris, vastus lateralis, vastus medialis and rectus femoris during the Monopodal Squat, Forward Lunge and Lateral Step-Up exercises. PloS one. 15, e0230841 (2020). https://doi.org/10.1371/journal.pone.0230841
Monajati, A., Larumbe-Zabala, E., Goss-Sampson, M., and Naclerio, F. (2019). Surface Electromyography Analysis of Three Squat Exercises. J Hum Kinet. 67, 73–83 (2019). https://doi.org/10.2478/hukin-2018-00731.
Escamilla R. F. Knee biomechanics of the dynamic squat exercise. Med Sci Sports Exerc. 33, 127–141 (2001). https://doi.org/10.1097/00005768-200101000-00020.
Lanshammar, K., and Ribom, E. L. Differences in muscle strength in dominant and non-dominant leg in females aged 20-39 years--a population-based study. Phys Ther Sport. 12, 76–79 (2011). https://doi.org/10.1016/j.ptsp.2010.10.004.
Häkkinen, K., and Keskinen, K. L. Muscle cross-sectional area and voluntary force production characteristics in elite strength- and endurance-trained athletes and sprinters. Eur J Appl Physiol Occup Physiol. 59, 215–220 (1989). https://doi.org/10.1007/BF02386190.
Bryanton, M. A., Kennedy, M. D., Carey, J. P., and Chiu, L. Z. Effect of squat depth and barbell load on relative muscular effort in squatting. J Strength Cond Res. 26, 2820–2828 (2012). https://doi.org/10.1519/JSC.0b013e31826791a7.
Campos, G. E et al.. Muscular adaptations in response to three different resistance-training regimens: specificity of repetition maximum training zones. Eur J Appl Physiol. 88(1-2), 50–60 (2002). https://doi.org/10.1007/s00421-002-0681-6.

No competing interests reported.

SupplementaryS1.tif

Comparison of the effects of 6-week progressive bodyweight and barbell-back squat programs on lower limb muscle strength, muscle thickness, and body fat percentage among sedentary young women

Status:

Journal Publication

Version 1

Abstract

Figures

Introduction

Method