The mechanisms of muscle hypertrophy and their application to resistance training

Effects of protein supplementation on muscle mass, muscle strength, and physical performance in older adults with physical inactivity: a systematic review and meta-analysis

BACKGROUND

Maintaining skeletal muscle mass and function in older adults is of paramount importance for preserving both quality of life and overall health. Exercise is essential for muscle maintenance; however, for older individuals with comorbidities, engaging in physical exercise may pose challenges due to decreased endurance and the inability to reach optimal exercise intensities. Several studies have investigated the effects of protein supplementation on muscle mass, strength, and physical performance in older adults. However, the results are inconsistent. The objective of this study was to systematically review and synthesize the effects of protein supplementation on muscle mass, muscle strength, and physical performance in physically inactive older adults.

METHODS

Four databases (PubMed, EMBASE, Web of Science and the Cochrane Central Registry of Controlled Trials) were systematically searched from inception to 31 January 2025. Two reviewers independently conducted the study screening, data extraction, risk of bias and GRADE assessments. In accordance with the PRISMA guidelines, the outcome data were synthesized using meta-analysis via RevMan5.4 software or a narrative method.

RESULTS

Eight data groups from six randomized controlled trials(RCTs) were included in the analysis, stratifying participants into three physical activity(PA) trajectories: sustained low PA (n= 1), transition to structured training from low PA (n= 4), and a shift from moderate to low PA (n= 3). Protein supplementation had no statistically significant effect on total lean body mass (p> 0.05). Furthermore, secondary muscle mass parameters showed negligible intervention benefits, whereas heterogeneous outcomes were observed across muscle strength and physical performance metrics.

CONCLUSIONS

The influence of protein on muscle mass was not significantly efficacious, and mixed results were shown for muscle strength and physical performance. Further well-designed studies are needed to determine the effectiveness of protein supplementation to maximize its potential benefits in older individuals with physical inactivity.

TRIAL REGISTRATION

This study was registered at www.crd.york.ac.uk/prospero/(registration no. CRD42024504443).

Current methods for the exercise dose equalization in resistance training drive to markedly different session-induced efforts

BACKGROUND

Effects comparison of resistance exercises may require equalizing the exercise-induced dose, this is currently done by using methods based on total weight lifted or on sets performed until failure. Dose equalization of resistance training sessions by these methods was analyzed in the present study.

METHODS

Twelve trained participants performed five bench-press sessions with a similar relative endpoint determined by the inability to complete a set of 50% of the maximum repetitions number (MNR). Sessions were performed at 50 or 85% of one-repetition maximum (1-RM) with sets until failure or sets prescribing 50% of MNR. The last session was performed with a reduced recovery pause to match the exercise density (total weight lifted/pause duration) of a previous session.

RESULTS

Sessions resulted in different total weight lifted (3158±1592 kg at 85% of 1-RM vs. 5330±1967 at 50%, P<0.001) and number of sets until failure (5.1±1.9 at 85% of 1-RM vs. 2.9±1.1 at 50%, P<0.001). Matching of sessions' density suppressed the differences in the number of sets performed (P=0.50).

CONCLUSIONS

Protocols' equalization based on the total weight lifted is likely to result in exercise volumes close to maximums when performed with heavy loads, whereas equalization based on sets to failure could induce a sets number close to the maximum when performed with light loads. Current methods for protocols equalization rely on gross values of exercise volume without considering maximums, that can result in markedly unbalanced efforts and biased results. Prescribing each exercise volume according to its maximum might optimize the training protocols' equalization.

Stiff and self-healing hydrogels by polymer entanglements in co-planar nanoconfinement

Many biological tissues are mechanically strong and stiff but can still heal from damage. By contrast, synthetic hydrogels have not shown comparable combinations of properties, as current stiffening approaches inevitably suppress the required chain/bond dynamics for self-healing. Here we show a stiff and self-healing hydrogel with a modulus of 50 MPa and tensile strength up to 4.2 MPa by polymer entanglements in co-planar nanoconfinement. This is realized by polymerizing a highly concentrated monomer solution within a scaffold of fully delaminated synthetic hectorite nanosheets, shear oriented into a macroscopic monodomain. The resultant physical gels show self-healing efficiency up to 100% despite the high modulus, and high adhesion shear strength on a broad range of substrates. This nanoconfinement approach allows the incorporation of novel functionalities by embedding colloidal materials such as MXenes and can be generalized to other polymers and solvents to fabricate stiff and self-healing gels for soft robotics, additive manufacturing and biomedical applications.

Knee flexion range of motion does not influence muscle hypertrophy of the quadriceps femoris during leg press training in resistance-trained individuals

This study investigated the effect of knee flexion range of motion (ROM) during the leg press exercise on quadriceps femoris muscle hypertrophy in resistance-trained individuals. Twenty-three participants (training age: 7.2 ± 3.5 years) completed a within-participant design, performing four sets of unilateral leg presses to momentary failure twice weekly for 8 weeks. In one leg, the knee flexion range of motion (ROM) was fixed at approximately 5-100°, while for the other leg, participants used their maximum individualized ROM (5-154 ± 7.8°). Quadriceps muscle thickness was assessed via B-mode ultrasonography in the proximal, central, and distal regions of the mid- and lateral thighs. Bayesian analyses were conducted to quantify treatment effects and provide inferential estimates using credible intervals and Bayes Factors (BF). Univariate and multivariate analyses indicated 'moderate' (BF = 0.14 to 0.22) and 'extreme' (BF < 0.01) evidence in support of the null hypothesis, respectively. Within-condition analyses revealed small-to-medium hypertrophic adaptation in both conditions, with absolute increases ranging from 1.08 mm to 1.91 mm. These findings suggest that both knee flexion ROMs are similarly effective for promoting quadriceps femoris muscle hypertrophy over a relatively short training-period in resistance-trained individuals.

Impact of High-Intensity Sports Practice on Stomatognathic System Function: An Observational Study

Background: Physical activity improves quality of life, but competitive sports emphasize performance, leading to intense training and restrictive diets that increase injury risk. This affects the stomatognathic system, underscoring the role of sports dentistry in preventing injuries and orofacial functional changes. This observational study analyzed the stomatognathic system's functionality in male high-intensity athletes (n = 18) compared to a sedentary group (n = 18). Methods: Functional parameters were analyzed: electromyographic activity during mandibular tasks, masseter and temporal muscles thickness, and molar bite force. Results: Student's t-test was used for analysis. At mandibular rest, male high-performance athletes showed lower electromyographic activity in the right and left masseter muscles, suggesting adaptation to training. During maximum voluntary contraction, activity was higher in the temporal and masseter muscles, especially in the left masseter, indicating hypertrophy. Electromyographic activity increased during protrusion and lateral movements, particularly in the masseter and temporal muscles, demonstrating a greater functional efficiency group of athletes. They also exhibited greater masseter muscle thickness and thinner temporal muscle thickness, with a significant difference in the right masseter muscle at rest. The group of athletes showed greater molar bite force, with significant differences, indicating greater muscle capacity. Conclusions: Sports practice promotes adaptations in the stomatognathic system, improving its functionality.

Autonomic modulation and skeletal muscle oxygenation with intermittent low-load blood flow restriction knee extension

Introduction

This investigation determined if an acute bout of low-load knee extension (KE) with intermittent blood flow restriction (BFR) influenced autonomic modulation and skeletal muscle oxygenation (SmO2%).

Methods

Fourteen physically active males completed three different sessions: one-repetition maximum (1RM), KE with BFR (BFR-KE) at 20% 1RM (cuff pressure=143 ± 13 mmHg), and KE with free blood flow at 20% 1RM (Control-KE). Heart rate variability (HRV) metrics: logarithmically transformed (ln) square root of the mean differences of successive R-R intervals (lnRMSSD), high frequency power (lnHF), and low frequency power (lnLF), as well as SmO2%, and rating of perceived exertion (RPE) were measured. Repeated measures analyses of variance were used to analyze HRV metrics and SmO2%, while a paired t-test was used to analyze RPE. A significance level of P < 0.05 was used for analyses.

Results

From baseline to 15 min post-exercise lnRMSSD decreased in both BFR-KE and Control-KE (4.34 ± 0.43-3.75 ± 0.82 ms, P = 0.027). Thereafter, lnRMSSD (+7%), lnHF (+8%), and lnLF (+7%) increased from 15 to 30 min post-exercise in both BFR-KE and Control-KE (P < 0.05). BFR-KE reduced SmO2% in the vastus lateralis compared to Control-KE (36% vs. 53%; P < 0.001). RPE was greater in BFR-KE (7.0 AU) compared to Control-KE (4.5 AU; P < 0.001).

Conclusion

Unilateral BFR exercise with individualized cuff pressure and intermittent application facilitated greater localized muscular stress and perceptual effort, but there was no influence of vascular occlusion on post-exercise autonomic modulation compared to volume-matched exercise with free blood flow.

The effects of regular training on spinal posture: a fitness and bodybuilding perspective

Background

Regular training is associated with better postural alignment, decreased risk of musculoskeletal problems, and improved overall physical function. The aim of this study was to examine the changes in the spinal postures of individuals who regularly engage in fitness and bodybuilding training.

Methods

A total of 252 male individuals between the ages of 20-28 (mean age: 23.71 ± 1.81 years), who either engage in fitness and bodybuilding training (athletes) (n = 125; age 23.61 ± 1.78 years; sports age 5 ± 0.89 years) and those who do not engage in sports (sedentary) (n = 127; age 23.82 ± 1.83 years) participated in the study. A spinal Mouse device was used in the measurements. In spine measurement, all spinal protrusions from C7 to S1 were evaluated. T-test and correlation tests were used to analyze the data.

Results

A statistically significant difference was detected between the athlete and sedentary groups regarding the degrees of thoracic kyphosis, lumbar lordosis, and sacral kyphosis (p < 0.05). However, no difference was observed in the upright posture (p > 0.05).

Conclusion

It was found that there were significant differences in some spinal curves of fitness and bodybuilding trainees compared to sedentary, but the values were within physiological limits and did not indicate negative effects. The study may provide new insights into the effects of fitness and bodybuilding training on spine health, and individuals can incorporate training with proper form and technique into their lifestyle for spinal health.

Multimodal Adaptations to Expiratory Musculature-Targeted Resistance Training: A Preliminary Study in Healthy Young Adults

PURPOSE

Exercise-induced adaptations, including neuroplasticity, are well studied for physical exercise that targets skeletal muscles. However, little is known about the neuroplastic potential of targeted speech and swallowing exercises. The current study aimed to gather preliminary data on molecular and functional changes associated with the neuroplastic effects of 4-week expiratory musculature-targeted resistance training in healthy young adults.

METHOD

Five healthy young adult men aged between 19 and 35 years, M (SD) = 28.8 (2.68) years, underwent 4 weeks of expiratory muscle strength training (EMST). We measured changes in maximum expiratory pressure (MEP), serum brain-derived neurotrophic factor (BDNF), and insulin-like growth factor 1 (IGF-1) levels at baseline and posttraining conditions. Furthermore, functional and structural magnetic resonance images were obtained to investigate the neuroplastic effects of EMST. We analyzed the effects of training using a linear mixed model for each outcome, with fixed effects for baseline and posttraining.

RESULTS

MEP and serum BDNF levels significantly increased posttraining. However, this effect was not observed for IGF-1. A significant increase in functional activation in eight regions was also observed posttraining. However, we did not observe significant changes in the white matter microstructure.

CONCLUSIONS

Preliminary data from our study suggest targeted resistance training of expiratory muscles results in molecular and neuroplastic adaptations similar to exercise that targets skeletal muscles. Additionally, these results suggest that EMST could be a potential intervention to modulate (or prime) neurotrophic signaling pathways linked to functional strength gains and neuroplasticity.

Nutritional Interventions to Attenuate Quadriceps Muscle Deficits following Anterior Cruciate Ligament Injury and Reconstruction

Following anterior cruciate ligament (ACL) injury, quadriceps muscle atrophy persists despite rehabilitation, leading to loss of lower limb strength, osteoarthritis, poor knee joint health and reduced quality of life. However, the molecular mechanisms responsible for these deficits in hypertrophic adaptations within the quadriceps muscle following ACL injury and reconstruction are poorly understood. While resistance exercise training stimulates skeletal muscle hypertrophy, attenuation of these hypertrophic pathways can hinder rehabilitation following ACL injury and reconstruction, and ultimately lead to skeletal muscle atrophy that persists beyond ACL reconstruction, similar to disuse atrophy. Numerous studies have documented beneficial roles of nutritional support, including nutritional supplementation, in maintaining and/or increasing muscle mass. There are three main mechanisms by which nutritional supplementation may attenuate muscle atrophy and promote hypertrophy: (1) by directly affecting muscle protein synthetic machinery; (2) indirectly increasing an individual's ability to work harder; and/or (3) directly affecting satellite cell proliferation and differentiation. We propose that nutritional support may enhance rehabilitative responses to exercise training and positively impact molecular machinery underlying muscle hypertrophy. As one of the fastest growing knee injuries worldwide, a better understanding of the potential mechanisms involved in quadriceps muscle deficits following ACL injury and reconstruction, and potential benefits of nutritional support, are required to help restore quadriceps muscle mass and/or strength. This review discusses our current understanding of the molecular mechanisms involved in muscle hypertrophy and disuse atrophy, and how nutritional supplements may leverage these pathways to maximise recovery from ACL injury and reconstruction.

What are the potential mechanisms of fatigue-induced skeletal muscle hypertrophy with low-load resistance exercise training?

High-load resistance exercise (>60% of 1-repetition maximum) is a well-known stimulus to enhance skeletal muscle hypertrophy with chronic training. However, studies have intriguingly shown that low-load resistance exercise training (RET) (≤60% of 1-repetition maximum) can lead to similar increases in skeletal muscle hypertrophy as compared with high-load RET. This has raised questions about the underlying mechanisms for eliciting the hypertrophic response with low-load RET. A key characteristic of low-load RET is performing resistance exercise to, or close to, task failure, thereby inducing muscle fatigue. The primary aim of this evidence-based narrative review is to explore whether muscle fatigue may act as an indirect or direct mechanism contributing to skeletal muscle hypertrophy during low-load RET. It has been proposed that muscle fatigue could indirectly stimulate muscle hypertrophy through increased muscle fiber recruitment, mechanical tension, ultrastructural muscle damage, the secretion of anabolic hormones, and/or alterations in the expression of specific proteins involved in muscle mass regulation (e.g., myostatin). Alternatively, it has been proposed that fatigue could directly stimulate muscle hypertrophy through the accumulation of metabolic by-products (e.g., lactate), and/or inflammation and oxidative stress. This review summarizes the existing literature eluding to the role of muscle fatigue as a stimulus for low-load RET-induced muscle hypertrophy and provides suggested avenues for future research to elucidate how muscle fatigue could mediate skeletal muscle hypertrophy.

The effect of resistance training on blood pressure and resting heart rate in type 2 diabetes: A systematic review and meta-analysis of randomized controlled trials

This meta-analysis assessed the impacts of resistance training on hemodynamic outcomes, including blood pressure and heart rate, in patients with type 2 diabetes (T2D). Four databases were searched following PRISMA guidelines. Randomized controlled trials (RCTs) comparing resistance training to usual care were included if they evaluated systolic and diastolic blood pressure (SBP and DBP), heart rate, and maximum oxygen uptake (VO2max) in adults with T2D. Random-effects models were used to calculate mean differences, with corresponding 95 % confidence intervals (CIs). Twenty-six RCTs were included. Resistance training significantly reduced SBP by -4.13 mmHg (95 % CI: -6.40, -1.85; p = 0.0004) and DBP by -2.03 mmHg (95 % CI: -3.69, -0.38; p = 0.02), with greater reductions in interventions lasting over 12 weeks. Resting heart rate decreased by -3.17 bpm (95 % CI: -6.33, -0.01; p = 0.05) and VO2max improved by 0.27 ml/kg/min (95 % CI: 0.02, 0.53; p = 0.04). Meta-regression revealed that intervention duration, session frequency, and study quality did not significantly explain the observed heterogeneity. Resistance training effectively improves hemodynamic outcomes T2D patients, but high heterogeneity in blood pressure outcomes and limited subgroup data on specific subgroups (e.g., women) restrict generalizability. Further research should explore heterogeneity sources and optimize resistance training protocols.

Do Cheaters Prosper? Effect of Externally Supplied Momentum During Resistance Training on Measures of Upper Body Muscle Hypertrophy

Exercise technique, defined as the controlled execution of bodily movements to ensure an exercise effectively targets specific muscle groups while minimizing the risk of injury, is a resistance training (RT) variable frequently highlighted as critical to successful RT program outcomes, with proper technique suggested to play a role in maximizing muscle development. This study examined the effects of externally applied momentum on RT-induced muscular adaptations in the upper extremities. Thirty young adults were recruited to participate in a within-participant design, with one limb randomly allocated to perform biceps curls and triceps pushdowns using strict form (STRICT) and the other using external momentum (CHEAT). Participants completed four sets of each exercise with 8-12 repetitions until momentary muscular failure, twice a week for eight weeks. We obtained pre-post proximal and distal measures of muscle thickness for the elbow flexors and extensors, and assessed circumference changes in the upper arms. Data were analyzed in a Bayesian framework including both univariate and multivariate mixed effect models with random effects. Differences between conditions were estimated as average treatment effects, with inferences based on posterior distributions and Bayes Factors (BFs). Results showed similar between-conditions increases for all muscle thickness sites as well as circumference measures, generating consistent support for the null hypothesis (BF = 0.06 to 0.61). Volume load was markedly greater for CHEAT compared to STRICT across each week of the intervention. In conclusion, the use of external momentum during single-joint RT of the upper extremities neither helped nor hindered hypertrophy of the target muscles.

Investigation of the effect of a virtual reality-based imagery training model on muscle activation in athletes

Introduction

In the field of sports psychology, imagery training plays a significant role in enhancing athletes' mental preparation and optimizing sports performance. This study aims to investigate the effects of the Virtual Reality-Based Imagery (VRBI) training model on muscle activation and kinesthetic motor imagery skills in athletes. Specifically, the study compares the VRBI model with traditional imagery methods, including Visual Motor Behavior Practice (VMBP) and Video Modeling (VM), to determine its effectiveness in improving neuromuscular responses.

Methods

A quasi-experimental design with repeated measures was employed, involving 30 bodybuilders and fitness athletes who were randomly assigned to VRBI, VMBP+VM, and control groups. Muscle activation was measured using surface electromyography (sEMG) across a 12-week intervention period. The intervention protocols included progressive relaxation, video modeling, and imagery exercises tailored to enhance kinesthetic motor imagery skills.

Results

The results revealed that the VRBI model significantly increased muscle activation levels and kinesthetic motor imagery skills compared to both the VMBP+VM and control groups (p < 0.01). Notably, athletes in the VRBI group achieved peak muscle activation one week earlier than those in the VMBP+VM group, demonstrating a faster adaptation process. Additionally, VRBI training led to a more substantial improvement in imagery skills, suggesting its superiority in mental training interventions.

Discussion and conclusion

The VRBI model offers a more effective approach to enhancing muscle activation and kinesthetic motor imagery skills in athletes. These findings highlight the potential of VRBI as a valuable tool for optimizing sports performance and accelerating peak performance achievement.

The effects of high protein intakes during energy restriction on body composition, energy metabolism and physical performance in recreational athletes

BACKGROUND

Athletes employ weight loss practices to lower body fat and maintain fat-free mass (FFM). High protein diets have been shown to produce greater fat loss and retention of lean mass during periods of energy restriction (ER) in sedentary individuals with obesity, but less is known about the effects of high protein diets in trained individuals during ER. Although current recommendations for protein intake in active individuals are 1.2-1.7 g/kg, it is unclear whether higher intakes are necessary to maximize FFM retention and maximize physical performance in athletes undergoing periods of ER.

OBJECTIVE

Determine whether high protein intakes could maximize FFM retention and physical performance in trained individuals after a period of ER.

METHODS

Twenty-one college aged athletes underwent a 6-week 25% ER + 3-day full body resistance training. Participants were randomly assigned to a low (~1.2 g/kg), moderate (~1.6 g/kg) or high (~2.2 g/kg) protein intake. Baseline and post-intervention outcomes: Dual X-ray absorptiometry, isotopic water dilution, indirect calorimetry, dietary records and strength based physical testing.

RESULTS

Significant reductions in body mass (p = 0.047) and fat mass (p = 0.04) with simultaneous increases in FFM (p = 0.037) were noted for all groups, with no protein intake effect. Significant increases in physical performance outcomes (5RM strength) were noted for most measures (p < 0.05).

CONCLUSION

Current protein intake recommendations of 1.2-1.7 g/kg appear sufficient for most athletes even during periods of ER to maintain FFM and physical performance.

Effects of Accentuated Eccentric and Maximal Strength High-Resistance Training Programs with or Without a Curcumin-Based Formulation Supplement on Body Composition, Blood Pressure, and Metabolic Parameters in Older Adults

BACKGROUND/OBJECTIVES

This study compared the effects of high-resistance training (RT) programs, with or without curcumin supplementation, on variables commonly associated with metabolic syndrome (MetS), including body composition, blood pressure, and metabolic parameters.

METHODS

Eighty-one older adults at risk of MetS (BMI > 25 kg/m2, fat mass > 32%, and systolic blood pressure > 130 mmHg in half of the participants) were randomly assigned to six groups, which were comprised as follows: four experimental groups involving either accentuated eccentric or maximal strength RT with curcumin or placebo and two control groups receiving either curcumin or placebo. Experimental groups completed a 16-week full-body RT with elastic bands, while controls did not exercise.

RESULTS

The results showed that (I) all experimental protocols significantly reduced fat mass (p ≤ 0.001), with the maximal strength RT group supplemented with curcumin (Max-Cur) showing the greatest reduction, at 14.3%; (II) muscle gains were significant and comparable across experimental groups (p ≤ 0.008); (III) both systolic and diastolic blood pressure decreased similarly across experimental groups (p ≤ 0.001); (IV) metabolic parameters significantly improved across experimental groups (p ≤ 0.037), except for creatinine, which showed an undesirable peak only in the Max-Cur group; (V) curcumin supplementation enhanced the effects of both RT programs; and (VI) between 54% and 100% of participants achieved clinically meaningful improvements in seven out of ten MetS-related variables across experimental groups.

CONCLUSIONS

Our findings indicate that high-RT programs combined with curcumin supplementation positively impacted all MetS-related variables. The Max-Cur RT group stood out as the most beneficial, with the greatest fat mass reductions, highlighting this approach as a promising strategy to reduce the risk of MetS in older adults.

Passive dehydration reduces muscle thickness after resistance exercise

Dehydration-induced increased plasma osmolality (Posmo) alters whole body fluid balance which could alter resistance exercise (RE) induced intramuscular (IM) fluid shift.

PURPOSE

The purpose of the current report was to investigate the effect of dehydration on RE-induced change in whole body fluid balance in resistance trained (RT) men.

METHODS

Fourteen RT men performed two identical RE sessions, either in a hydrated (EUHY) or dehydrated (DEHY) state induced by a 24 hr fluid restriction. Total body fluid, urine osmolality (Uosmo), urine specific gravity (USG), Posmo, hematocrit (HCT), muscle thickness were measured and plasma volume (%ΔPV) was calculated using HCT.

RESULTS

A significant (p < 0.050) condition effect was observed for total body fluid and muscle thickness such that EUHY was 2.6% and 13.0% greater than DEHY, respectively. Significant time × condition effects were observed for Posmo, Uosmo, and USG. At all times, EUHY (collapsing for time: Posmo: 3.9%; Uosmo: 133.5%; USG: 1.6%) was lower than DEHY. A significant time effect was observed for %ΔPV. %ΔPV 5 min after RE was -12.5% lower than PRE.

CONCLUSION

Dehydration with RE altered whole body fluid balance indicated by greater fluid retention and efflux of IM fluid could at least partly maintain %ΔPV following DEHY in RT men.

Body Contouring With Electromagnetic Treatment Plus Radiofrequency: A Review

BACKGROUND

Electromagnetic treatments have recently been combined with radiofrequency to reduce the fat layer and simultaneously increase muscle thickness. Studies report treatment efficacy, using photographs and imaging methods.

METHODS

A literature review was conducted. Measurement data were tabulated. The EmSculpt Neo device (BTL Industries, Boston, MA) was used in all studies.

RESULTS

Seven studies evaluated the fat thickness and muscle thickness using either ultrasound (1 study) or magnetic resonance imaging methods (6 studies). The abdomen was treated in 2 studies. The other studies treated the lateral thighs, flanks, buttocks, inner thighs, and upper arms. The mean reduction in fat thickness was 8.0 mm, and the mean increase in muscle thickness was 5.5 mm. All 7 studies were authored by BTL medical advisors. Measured changes were likely within the margin of error and of questionable clinical relevance. Few adverse events were reported.

DISCUSSION

Photographs were frequently not standardized, showing changes in treated areas, but unexplained changes in nontreated areas as well. The magnetic resonance imaging scans were affected by differing levels of the axial slice. Measured changes were incremental and likely not indicative of a true treatment effect. The scientific basis for efficacy is tenuous, both for fat reduction and muscle hypertrophy.

CONCLUSIONS

A scientific evaluation of the results fails to produce reliable evidence of a clinically meaningful result for this combination energy-based treatment. Financial conflict is a major factor. Liposuction remains the gold standard.

Credibility of Blood Flow Restriction Training in Patients With Knee Osteoarthritis: A Systematic Review and Meta-analysis

Background

The effectiveness and practicality of blood flow restriction training (BFRT) as a nonsurgical intervention for treating patients with knee injuries are uncertain because of the small size of BFRT trials and inconsistent results.

Purpose

To conduct a meta-analysis comparing the effectiveness of BFRT versus traditional resistance training in patients with knee osteoarthritis (OA) in terms of pain, muscle strength, functional performance, self-reported function, muscle size, and adverse events during exercise.

Study Design

Systematic review; Level of evidence: 1.

Methods

Under the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, we searched the Web of Science, PubMed, EMBASE, and other databases for randomized controlled trials of BFRT interventions in patients with knee OA. Methodological and quality evaluations, heterogeneity analysis, and subgroup analysis of the included studies were conducted, and effect sizes were evaluated using mean differences or standardized mean differences (SMDs). Subgroup and sensitivity analyses were used to explore the sources of heterogeneity.

Results

Of 2826 initial studies, 6 studies (N = 228 patients) were included. The results of the meta-analysis indicated that compared with resistance training, BFRT did not significantly affect pain relief (SMD, -0.02 [95% CI, -0.30 to 0.26]; P = .88), muscle strength (SMD, 0.32 [95% CI, -0.33 to 0.96]; P = .33), functional performance (SMD, 0.25 [95% CI, -0.29 to 0.80]; P = .36), or self-reported function (SMD, -0.252 [95% CI, -0.88 to 0.45]; P = .52). However, BFRT reduced the risk of adverse events (risk ratio, 0.45 [95% CI, 0.20 to 1.01]; P = .05). Subgroup analysis revealed that compared with low-load resistance training, BFRT significantly increased muscle size (SMD, 0.88 [95% CI, 0.09 to 1.68]; P = .02). The quality-of-evidence assessment indicated that the evidence level for the above outcomes was low and that the strength of the recommendation was weak.

Conclusion

The results of our meta-analysis indicated that compared with resistance training, BFRT did not significantly improve symptom outcomes in patients with knee OA. It is important to acknowledge that the findings were limited by the small number of studies and sample sizes that were included.

Impact of exercise with blood flow restriction on muscle hypertrophy and performance outcomes in men and women

Blood flow restriction training (BFRT) has been previously studied as an alternative form of resistance training to gain lean mass and improve performance outcomes. However, in all exercise studies of BFRT, the proportion of female participants represents only 17-29% of all research participants. This highlights a strong underrepresentation of females and the need for more knowledge on the impact of BFRT and sex differences. The primary objective was to compare the impact of 6-week BFRT on lean mass, strength, and performance outcomes between males and females. A total of 38 adults [age, 25.3 ±  3.1 years; female, n = 19 (50%)] performed whole-body resistance training program with blood flow restriction three times per week. Exercises were performed at 30% of 1-repetition maximum (1-RM) and blood flow restriction cuffs were set to 60% of each individual's limb occlusion pressure. Body composition was assessed via dual-energy x-ray absorptiometry and strength was measured using 1-RM. A significant increase in lean mass was observed in males (p = 0.009) and females (p = 0.023) with no difference in the change between groups (p = 0.279). Both males and females increased 1-RM for upper- and lower-body exercises, with significant interaction effects (time x sex) for chest press (p = 0.003), seated row (p = 0.038), knee flexion (p = 0.043), and knee extension (p = 0.035), suggesting males increased 1-RM more for these exercises. Furthermore, peak power was improved in males (p < 0.001) and females (p = 0.002) during a vertical squat jump, but a significant interaction (time x sex) effect was observed (p = 0.039), suggesting males increased to a greater extent. Males and females significantly increased lean body mass, to a similar degree, following six weeks of resistance training in combination with blood flow restriction. Likewise, both males and females improved muscle strength following 6-week BFRT, however males may improve strength to a greater extent than females.

Conceptualizing a load and volume autoregulation integrated velocity model to minimize neuromuscular fatigue and maximize neuromuscular adaptations in resistance training

Resistance training (RT) load and volume are considered crucial variables to appropriately prescribe and manage for eliciting the targeted acute responses (i.e., minimizing neuromuscular fatigue) and chronic adaptations (i.e., maximizing neuromuscular adaptations). In traditional RT contexts, load and volume are generally pre-prescribed; thereby, potentially yielding sub-optimal outcomes. A RT concept that individualizes programming is autoregulation: a systematic two-step feedback process involving, (1) monitoring performance and its constituents (fitness, fatigue, and readiness) across multiple time frames (short-, moderate-, and long-term); and (2) adjusting programming (i.e., load and volume) to elicit the targeted goals (i.e., responses and adaptations). A growing body of load and volume autoregulation research has accelerated recently, with several meta-analyses suggesting that autoregulation may provide a small advantage over traditional RT. Nonetheless, the existing literature has typically conceptualized these current autoregulation methods as standalone practices, which has limited their extensive utility in research and applied settings. The primary purpose of this review was three-fold. Initially, we synthesized the current methods of load and volume autoregulation, while disseminating each method's main advantages and limitations. Second, we conceptualized a theoretical Integrated Velocity Model (IVM) that integrates the current methods for a more holistic perspective of autoregulation that may potentially augment its benefits. Lastly, we illustrated how the IVM may be compared to the current methods for future directions and how it may be implemented for practical applications. We hope that this review assists to contextualize a novel autoregulation framework to help inform future investigations for researchers and practices for RT professionals.

Eccentric strengthening vs. conventional therapy in sub-acute stroke survivors: a randomized controlled trial

Spastic paresis, a frequent consequence of stroke, is characterized by both neurological and muscular alterations, leading to decreased muscle strength, increased passive muscle stiffness, and subsequently, diminished functional capacity. Although conventional rehabilitation programs are effective in enhancing muscle strength, they often fail to yield clinically significant improvements in functional capacities. Eccentric Training (ET) has shown promise in addressing the shortened muscle fascicle lengths and joint contractures commonly observed in stroke survivors. Despite the prevalence of contractures and rigidity in this population, the effects of ET on the structural and mechanical properties of muscles remain underexplored. This study aims to investigate the impact of ET on gait speed in sub-acute stroke patients compared to conventional therapy. Additionally, we aim to explore the effects of ET on the mechanical properties, structural characteristics, and neuromuscular parameters of the plantar flexors. A randomized controlled trial will be conducted, adhering to CONSORT guidelines, with participants assigned to either a Conventional Therapy Group or an Eccentric Training Group. Assessments will be conducted at baseline, and after ET intervention, encompassing clinical, biomechanical, and functional evaluations. This study seeks to provide empirical evidence on the efficacy of ET in improving motor outcomes in sub-acute stroke patients, thereby informing more effective rehabilitation strategies.

The Effects of Floor Isometric Trunk Extension Exercise on Muscle Thickness and Activation Vary Between Different Combinations of Duration and Repetition Number

CONTEXT

Intermittent floor trunk extensions are popular exercises in group fitness programs. The aim of this study was to investigate whether fewer repetitions of longer isometric trunk extension efforts compared with more repetitions of shorter isometric contractions have different acute effects on muscle thickness and activation as well as perceived exertion.

DESIGN

This study followed a cross-sectional design.

METHODS

Twenty healthy young males performed floor prone trunk extension exercises using 3 different exercise protocols of repetition and duration: 10 × 5 seconds (D10 × 5), 2 × 25 seconds (D2 × 25), and 5 × 10 seconds (D5 × 10). Ultrasound multifidus thickness and rate of perceived exertion on a 10-point scale were measured immediately after each protocol. Electromyographic activation from the erector spinae, multifidus, and gluteus maximum during each protocol was measured using bipolar surface electrodes.

RESULTS

The longer duration (D2 × 25) protocol showed a significant greater rate of perceived exertion (6.22 [0.73]) and rest multifidus thickness change (median: 8.04%) compared with the other protocols (P < .05). Within each protocol, root mean square of all muscles increased from trial to trial in the D2 × 25 and D5 × 10 (P < .05), but not during the D10 × 5 protocol (P > .05). The maximum root mean square was achieved in the shorter duration (D10 × 5) protocol compared with the other ones (P < .05).

CONCLUSION

If trunk extension exercises on the floor are used in a training setting, then using exercises with long duration and fewer repetitions may elicit a greater metabolic response.

Effect of Eight-Week Transcranial Direct-Current Stimulation Combined with Lat Pull-Down Resistance Training on Improving Pull-Up Performance for Male College Students

The aim of this study was to investigate the effects and potential mechanisms of 8-week transcranial direct-current stimulation (tDCS) combined with resistance training (RT) on pull-up performance in male college students. Twenty-five male college students were randomly assigned to either RT combined with anodal tDCS stimulation (RT + tDCS) or RT alone (RT). Participants of both groups engaged in lat pull-down training programs for 8 weeks, with the RT + tDCS group receiving 20 min tDCS before each RT session. Pre- and post-intervention tests included pull-up endurance (number of repetitions), flexed arm circumference (FAC), and lat pull-down maximal voluntary isometric contraction (MVIC) peak force. During the pull-up endurance test, surface electromyography (sEMG) was recorded for the bicep brachii (BB), tricep brachii (TB), brachioradialis (BR), anterior deltoid (AD), middle deltoid (MD), posterior deltoid (PD), pectoralis major (PM), and latissimus dorsi (LD) muscles. Both groups demonstrated significant improvements in pull-up endurance and lat pull-down MVIC peak force after training, but no significant difference between the two groups was observed in the post-training test. Additionally, muscle activation of BR, PD, and PM decreased significantly in both groups, while the RT + tDCS group also demonstrated a significant reduction in TB coactivation after training. These findings suggest that eight weeks of tDCS combined with lat pull-down training and lat pull-down training alone can both significantly improve pull-up performance, which may be attributed to enhanced muscle contraction capacity. Although no significant training gains were found between the two training groups, the RT + tDCS group showed a significant decrease in TB coactivation and the enhancement of elbow flexion muscle contraction efficiency after training.

Muscle Strength and Size Relationships with Unilateral Progressive Resistance Training

Purpose

This study defines correlative and causal relationships between muscle strength and size before and after unilateral resistance training (RT) in a large cohort of healthy adults, focusing on sex differences within these relationships.

Methods

Results from 1233 participants (504 males and 729 females) in a retrospective analysis were included. Maximal voluntary isometric contraction strength (MVC), one-repetition maximum strength (1RM), biceps cross-sectional area (CSA) and elbow flexor volume (VOL) measures of the non-dominant and dominant arm were evaluated from baseline and after 12-wk RT twice per week. Correlations of MVC and VOL and 1RM and VOL were calculated in the whole cohort and within each sex independently. Causal analysis modeling was used to infer mechanistic relationships among variables.

Results

Absolute muscle strength and size related to one another both at baseline and following training, however correlation strength in each sex were weak. After RT, MVC relative change and VOL relative change correlations were correlated for the whole cohort (r=0.16; p<0.001) and females (r=0.18; p<0.001), but not in males (r=0.11; p=0.07). No significant correlations for relative change in 1RM and VOL were observed for the whole cohort or within sex. Causal discovery determined that change in VOL caused significant change in 1RM (but not MVC) and age was identified as a potential cause.

Conclusions

Sex differences occur in muscle size and strength relationship adaptations following resistance training, most notably the absence of significant relationships between relative size and strength changes in men. Simpson's paradox bias, where assessing the combined data of males and females (also affecting overall sample size) affects identifies patterns differently than assessing relationships within each sex, may partially explain our findings.

Reversing Decline in Aging Muscles: Expected Trends, Impacts and Remedies

Background: Age-related decline in musculoskeletal function is a significant concern, particularly in Western countries facing demographic shifts and increased healthcare demands. This review examines the typical trajectories of musculoskeletal deterioration with age and evaluates the effectiveness of various interventions in preventing or reversing these changes. Methods: The review analyzes documented rates of decline across multiple parameters, including muscle mass, Type II muscle fiber reduction, and decreased motor unit firing rates. It examines evidence from studies on targeted interventions aimed at reversing these trends or preventing further decline. Results: The evidence suggests that multimodal interventions, including strength training can effectively maintain or improve physical function in aging adults. These interventions have shown potential in altering the trajectory of age-related decline in musculoskeletal function. Conclusions. The findings of this review have important implications for healthcare providers and policymakers in addressing the challenges of an aging population. By providing a framework for understanding and addressing age-related physical decline through evidence-based interventions, this review offers potential strategies for reducing healthcare costs and improving the quality of life for older adults.

The impact of different exercise modalities on chronic kidney disease: an umbrella review of meta-analyses

Introduction

Exercise is widely recognized for its benefits to chronic kidney disease (CKD) patients. However, the specific impact of different exercise modalities on CKD-related outcomes remains unclear. This study sought to summarize the effects of different exercise modalities on the main outcomes impacted by CKD.

Methods

We searched for systematic review with meta-analysis in PubMed, Embase, Web of Science, Scopus, and Cochrane databases. We evaluated the methodological quality of included studies by AMSTAR2 tool and by individually evaluating the heterogeneity, sample power, and statistical significances from meta-analyses.

Results

We included 44 meta-analyses, encompassing 35,432 CKD patients in pre-dialysis and dialysis stages (peritoneal and hemodialysis). Data from meta-analyses with highly suggestive or strong evidence grading suggests that aerobic and combined training were most effective in improving cardiorespiratory fitness (main effect: 2.1, 95% CI: 0.8-3.4, and main effect: 3.4; 95% CI: 2.4-4.6, respectively). Combined training showed a consistent benefit in psychosocial domains (main effect: -7.3; 95% CI: -9.31 to -53). All exercise modalities significantly improve functional performance, except isometric training, which impacted just fistula maturation (main effect: 0.84; 95% CI: 0.5-1.2).

Conclusion

Exercise emerges as a potential non-pharmacological therapy for CKD patients. Tailoring exercise to specific outcomes appears to be crucial, as different exercise modalities exhibit varying effectiveness.

Effectiveness of resistance training on body composition, muscle strength, and biomarker in sarcopenic older adults: A meta-analysis of randomized controlled trials

This study analyzed 22 randomized controlled trials involving 959 participants to determine the impact of resistance training (RT) on body composition, muscle strength, and biomarkers in sarcopenic older adults. Regarding body composition, RT had a small effect size on relative muscle mass (RMM, SMD = 0.25[0.06,0.45]) and absolute muscle mass (AMM, SMD = 0.28[0.06,0.50]) but no effect on reducing body fat percentage (BF%). Meta-regression analysis pinpointed key predictors (p < 0.05): training period, number of sets, contraction speed, and average age. Subgroup analysis revealed that 3 sets over an 8-12 weeks training period, with slower muscle contraction speed at a 60-70 % 1-repetition maximum (1RM) training intensity, produced the most significant effects on reducing BF% and increasing RMM, respectively. Regarding muscle strength, RT had a large effect size on handgrip strength (HS, SMD = 0.83[0.43,1.23]), knee extension strength (KES, SMD = 0.90[0.50,1.30]), but no effect on chair stand test. Meta-regression analysis pinpointed key predictors (p < 0.05): training intensity, number of sets, body mass index, and sample size. Subgroup analysis revealed that the number of sets ≥ 3 and training intensity >70 % 1RM produced the most significant effect of RT on HS. Regarding biomarkers, RT had a medium effect size on insulin-like growth factor-1 (SMD = 0.70[0.10,1.30]), interleukin-10 (SMD = 0.61[0.09,1.13]), follistatin (SMD = 0.56[0.16,0.96]), but no effect on interleukin-6, tumor necrosis factor-alpha, and myostatin. It concludes that RT is an effective way to improve muscle strength and the level of synthetic hormones and anti-inflammatory factors in sarcopenic older adults, with a slight impact on body composition and no impact on pro-inflammatory factors.

The Impact of Stance Width on Kinematics and Kinetics During Maximum Back Squats

ABSTRACT

Larsen, S, Zee, Md, and Tillaar, Rvd. The impact of stance width on kinematics and kinetics during maximum back squats. J Strength Cond Res 39(1): 1-9, 2025-This study compared the lower extremity peak net joint moments (NJMs) and muscle forces between wide and narrow stance widths defined as 1.7 and 0.7 acromion width in the last repetition of the concentric phase in 3 repetition maximum back squats. Twelve recreationally trained men (age:25.3 ± 2.9 years, height:179 ± 7.7 cm, body mass:82.8 ± 6.9 kg) volunteered for the study. The NJMs were estimated using inverse dynamics and individual muscle forces with static optimization. The main findings of interest were that the wide stance resulted in statistically smaller knee flexion angles (Cohen's d: 0.9; 95% confidence interval [CI]: -17.96 to -3.18°), knee extension NJMs [d: 1.45; 95% CI: -1.56 to -0.61 Nm·kg-1], and vastii forces [d: 1.3; 95% CI: -27.7 to -0.9.5 N·kg-1] compared with the narrow stance. Moreover, we observed significantly larger hip abduction angles [d: 3.8; 95% CI: 12.04 to 16.86°] for the wide stance. Hence, we suggest that recreationally trained men aiming to optimize muscle forces in the vastii muscles during maximum back squat training should consider adopting a narrow stance.

The effects of hip flexion angle on quadriceps femoris muscle hypertrophy in the leg extension exercise

This study compared the effects of 90° versus 40° hip flexion in the leg extension exercise on quadriceps femoris muscle hypertrophy. Twenty-two untrained men completed a ten-week intervention comprising two resistance training sessions per week. A within-participant design was used, with the lower limb side randomly allocated to the 40 or 90° condition. Muscle thickness of distal and proximal rectus femoris and vastus lateralis was quantified via ultrasound. Data were analysed within a Bayesian framework including univariate and multivariate mixed effect models with random effects to account for the within participant design. Differences between conditions were estimated as average treatment effects (ATE) and inferences were made based on posterior distributions and Bayes Factors (BF). Results indicated a greater hypertrophic response in the rectus femoris for the 40° condition, with "extreme" evidence supporting a hypertrophic response favouring the 40° hip angle for the rectus femoris (BF > 100; p(Distal/ATE & Proximal/ATE >0) > 0.999), and "strong" evidence supporting no difference in hypertrophic response for the vastus lateralis (BF = 0.07). Therefore, both conditions could be viable options for increasing quadriceps femoris hypertrophy. However, when training for maximizing rectus femoris hypertrophy among untrained men, we suggest training with a reduced hip flexion in the leg extension exercise.

Individual muscle hypertrophy in high-load resistance training with and without blood flow restriction: A near-infrared spectroscopy approach

We aimed to compare individual hypertrophic responses to high-load resistance training (HL-RT) or high-load with blood flow restriction (HL-BFR). Furthermore, we investigated whether greater responsiveness to one of the protocols could be explained by acute changes in blood deoxyhemoglobin concentration (HHb) and total hemoglobin concentration (tHb) (proxy markers of metabolic stress). Ten untrained participants had their legs randomized into both HL-RT and HL-BFR and underwent 10 weeks of training. Muscle cross-sectional area (mCSA) was measured at baseline and post training, while HHb and tHb during the final session. Using a threshold of 2 × typical errors (3.24%) to compare protocols, five participants showed greater mCSA increases after HL-RT (16.44 ± 7.90%) compared to HL-BFR (10.74 ± 7.12%, p = 0.0054) and five did not respond better to HL-RT (8.95 ± 10.83%) compared to HL-BFR (13.33 ± 8.59%) (p = 0.3105). Additionally, HL-RT induced lower HHb (5855.78 ± 12905.99; p = 0.0101) and tHb (-43169.70 ± 37793.17; p = 0.0030) AUC values compared to HL-BFR (HHb: 39254.80 ± 27020.15; tHb: 46309.40 ± 31613.97). In conclusion, despite the higher levels of metabolic stress markers, most participants did not present greater muscle hypertrophy by combining blood flow restriction with HL-RT.

Impact of Five Weeks of Strengthening Under Blood Flow Restriction (BFR) or Supplemental Oxygen Breathing (Normobaric Hyperoxia) on the Medial Gastrocnemius

Background and Objectives: This study investigates the effects of a five-week training program on the medial gastrocnemius muscle, comparing two approaches: blood flow restriction (BFR) training and normobaric hyperoxia (oxygen supplementation). It evaluates three strengthening modalities (dynamic, isometric, and the 3/7 method) analyzing their impact on maximal voluntary contraction (MVC), muscle architecture, and perceived exertion. Methods: A total of 36 young healthy participants (21 females, 15 males) were randomized into six subgroups (n = 6 each) based on the type of contraction and oxygen condition. Training sessions (three per week) were conducted for five weeks at 30% of MVC. Measurements of MVC, muscle circumference, pennation angle, fascicle length, and perceived exertion were taken at baseline (T0), mid-protocol (T1), and post-protocol (T2). Results: All groups demonstrated significant increases in MVC after five weeks, with no notable differences between BFR and oxygen conditions. Structural changes were observed in specific subgroups: the BFR-isometric group showed increased calf circumference (p < 0.05), and the 3/7 groups exhibited significant fascicle length gains (p < 0.05). Perceived exertion was consistently higher in BFR groups compared to oxygen supplementation, particularly in dynamic exercises. Conclusions: Both BFR and oxygen supplementation are effective in enhancing strength with light loads, though they elicit different structural and perceptual responses. Oxygen supplementation may be more comfortable and less strenuous, offering a viable alternative for populations unable to tolerate BFR. Future research should focus on optimizing training parameters and exploring applications tailored to specific athletic or clinical contexts.

Acute Responses of Low-Load Resistance Exercise with Blood Flow Restriction

Blood flow restriction (BFR) is a popular resistance exercise technique purported to increase metabolic stress and augment training adaptations over time. However, short-term use may lead to acute neuromuscular fatigue and higher exertion ratings. Objective: The purpose of the current study was to examine acute physiological responses to low-load resistance exercise utilizing BFR compared to higher-load, non-BFR resistance exercise. Methods: Recreationally trained males (n = 6) and females (n = 7) (mean ± standard deviation, age: 20 ± 1 yrs.; height: 172 ± 8 cm; weight: 73 ± 11 kg; BMI: 24.4 ± 2.2 kg·m-2; training experience: 4 ± 2 yrs.) had limb occlusion pressure determined (50%; right leg: 118 ± 11 mmHg; left leg: 121 ± 13 mmHg) using an automated, self-inflating cuff system during baseline testing. In subsequent sessions, using a randomized, cross-over design, participants completed one of two experimental conditions: (1) Low-load + BFR and (2) High load + non-BFR. In both conditions, participants completed one set of back squats at either 30% (BFR) or 60% (non-BFR) of an estimated 1RM for a max of 30 repetitions, followed by three additional sets with the same loads and a target of 15 repetitions per set. Blood lactate and countermovement jump (CMJ) height were measured pre- and post-back squat. Ratings of perceived exertion (RPE) were assessed following each set. Results: When collapsed across all sets, participants completed significantly more total repetitions in the BFR condition compared to non-BFR (75.0 ± 0.0 vs. 68.23 ± 9.27 reps; p = 0.015; ES: 1.03), but a lower training load volume (2380 ± 728 vs. 4756 ± 1538 kg; p < 0.001; ES: 1.97). There was a significant time-by-condition interaction (p < 0.001), with a greater increase in blood lactate occurring from baseline to post-back squat in the non-BFR condition (11.61 mmol/L, 95%CI: 9.93, 13.28 mmol/L) compared to BFR (5.98 mmol/L, 95%CI: 4.30, 7.65 mmol/L). There was another significant time-by-condition interaction (p = 0.043), with a greater reduction in CMJ occurring in the non-BFR condition (-6.01, 95%CI: -9.14, -2.88 cm; p < 0.001) compared to BFR (-1.50, 95%CI: -1.50, 4.51 cm; p = 0.312). Conclusions: Utilizing a low-load BFR protocol may allow for a higher training volume, yet lower metabolic stress and reduce neuromuscular fatigue compared to lifting at a higher load without the use of BFR.

Effect of Fitness Level on Time Course of Recovery After Acute Strength and High-Intensity Interval Training

ABSTRACT

Grammenou, M, Kendall, KL, Wilson, CJ, Porter, T, Laws, SM, and Haff, GG. Effect of fitness level on time course of recovery after acute strength and high-intensity interval training. J Strength Cond Res 38(12): 2055-2064, 2024-The aim was to investigate time course of recovery after acute bouts of strength (STR) and high-intensity interval training (HIIT). A secondary goal was to assess the influence of total fitness score (TFS), composed of handgrip strength and maximum aerobic power on recovery. Twenty-eight resistance-trained individuals completed 8 testing sessions within a 14- to 17-day period. Subjects performed a testing battery comprising isometric midthigh pull (IMTP), countermovement jump (CMJ), and a modified Wingate test (WINmod) at baseline, immediately after exercise, as well as at 6 and 24 hours after the training sessions. A one-way ANOVA was performed to examine time changes after the training sessions. Subjects were then grouped based on their TFS in high, medium, and low groups. To examine the influence of TFS on time course of recovery, we performed a linear mixed-effects model. Statistical significance was set at p < 0.05. Both training sessions resulted in a significant reduction in peak force (PF) that persisted for up to 6 (p < 0.05) and 24 hours (p < 0.001). The STR session showed immediate and 24-hour postexercise declines in jump height and reactive strength index modified (RSImod) compared with baseline. The low TFS group exhibited a significant RSImod reduction immediately after HIIT (p < 0.001), compared with the medium TFS group (p = 0.0002). In the STR session, the high TFS group displayed an increased eccentric displacement during CMJ 24 hours after exercise compared with baseline (p = 0.033). Overall, subjects with high TFS may be able to recover CMJ performance at the same rate as other TFS groups, despite performing more work.

Feasibility and effectiveness of a 6-month, home-based, resistance exercise delivered by a remote technological solution in healthy older adults

BACKGROUND

Aging is characterized by a physiological decline in physical function, muscle mass, strength, and power. Home-based resistance training interventions have gained increasing attention from scientists and healthcare system operators, but their efficacy is yet to be fully determined.

AIMS

to verify the safety, feasibility, and efficacy of a home-based resistance training program delivered by innovative technological solution in healthy older adults.

METHODS

73 participants (36 females) were randomly allocated to either a control (C) or an intervention (I) group consisting of a 6-months home-based resistance training program delivered through an innovative technological solution, which included a wearable inertial sensor and a dedicated tablet. The safety and feasibility of the intervention were assessed by recording training-related adverse events and training adherence. Body composition, standing static balance, 10-meter walking, and loaded 5 sit-to-stand tests were monitored to quantify efficacy.

RESULTS

No adverse events were recorded. Adherence to the training program was relatively high (61 % of participants performed the target 3 sessions) in the first trimester, significantly dropping during the second one. The intervention positively affected walking parameters (p < 0.05) and maximal force (p = 0.009) while no effect was recorded on body composition, balance, and muscle power.

CONCLUSIONS

The home-based device-supported intervention was safe and feasible, positively affecting walking parameters and lower limbs' maximal force. This approach should be incentivized when barriers to participation in traditional resistance exercise programs are present.

Muscle Fat and Volume Differences in People With Hip-Related Pain Compared With Controls: A Machine Learning Approach

BACKGROUND

Hip-related pain (HRP) affects young to middle-aged active adults and impacts physical activity, finances and quality of life. HRP includes conditions like femoroacetabular impingement syndrome and labral tears. Lateral hip muscle dysfunction and atrophy in HRP are more pronounced in advanced hip pathology, with limited evidence in younger populations. While MRI use for assessing hip muscle morphology is increasing, with automated deep-learning techniques showing promise, studies assessing their accuracy are limited. Therefore, we aimed to compare hip intramuscular fat infiltrate (MFI) and muscle volume, in individuals with and without HRP as well as assess the reliability and accuracy of automated machine-learning segmentations compared with human-generated segmentation.

METHODS

This cross-sectional study included sub-elite/amateur football players (Australian football and soccer) with a greater than 6-month history of HRP [n = 180, average age 28.32, (standard deviation 5.88) years, 19% female] and a control group of sub-elite/amateur football players without pain [n = 48, 28.89 (6.22) years, 29% female]. Muscle volume and MFI of gluteus maximus, medius, minimis and tensor fascia latae were assessed using MRI. Associations between muscle volume and group were explored using linear regression models, controlling for body mass index, age, sport and sex. A convolutional neural network (CNN) machine-learning approach was compared with human-performed muscle segmentations in a subset of participants (n = 52) using intraclass correlation coefficients and Sorensen-Dice index.

RESULTS

When considering adjusted estimates of muscle volume, there were significant differences observed between groups for gluteus medius (adjusted mean difference 23 858 mm3 [95% confidence interval 7563, 40 137]; p = 0.004) and tensor fascia latae (6660 mm3 [2440, 13 075]; p = 0.042). No differences were observed between groups for gluteus maximus (18 265 mm3 [-21 209, 50 782]; p = 0.419) or minimus (3893 mm3 [-2209, 9996]; p = 0.21). The CNN was trained for 30 000 iterations and assessed its accuracy and reliability on an independent testing dataset, achieving high segmentation accuracy (mean Sorenson-Dice index >0.900) and excellent muscle volume and MFI reliability (ICC2,1 > 0.900). The CNN outperformed manual raters, who had slightly lower interrater accuracy (Sorensen-Dice index >0.800) and reliability (ICC2,1 > 0.800).

CONCLUSIONS

The increased muscle volumes in the symptomatic group compared with controls could be associated with increased myofibrillar size, sarcoplasmic hypertrophy or both. These changes may facilitate greater muscular efficiency for a given load, enabling the athlete to maintain their normal level of function. In addition, the CNNs for muscle segmentation was more efficient and demonstrated excellent reliability in comparison to manual segmentations.

Dynamic and Static Workout of In Vitro Skeletal Muscle Tissue through a Weight Training Device

Enhancing muscle strength through workouts is a key factor in improving physical activity and maintaining metabolic profiles. The controversial results concerning the impacts of weight training often arise from clinical experiments that require controlled experimental conditions. In this study, a weight training system for a muscle development model is presented, which is capable of performing weight training motions with adjustable weight loads. Through the implementation of cultured skeletal muscle tissue with floating structures and a flexible ribbon, both isotonic (dynamic change in muscle length) and isometric (static in muscle length) exercises can be performed without the deflection of the tissue. Quantitative analysis of contraction force, changes in metabolic processes, and muscle morphology under different weight training conditions demonstrates the effectiveness of the proposed system. Our proposed system holds potential for establishing effective muscle development and for further applications in rehabilitation training methods.

Similar adaptive responses in the upper body physical performance of table tennis players following the traditional and cluster set resistance and plyometric training

Numerous studies have investigated the impact of resistance training (RT) and plyometric training (PT) set configurations (cluster sets [CS] and traditional sets [TS]) on lower body performance adaptations. However, the effects of these training modalities on upper body physical performance, particularly among Table Tennis (TT) players, remain unclear. Therefore, this study aimed to examine the effects of an 8-week RT and PT using CS and TS configurations on the physical performance attributes of male TT players. Forty young male players were recruited from a local academy and after determining their dominant hand, divided into CS-PT, TS-PT, CS-RT, TS-RT, and active control (CON) groups, each of eight. Pre- and post-interventions, the upper body muscular power (medicine ball throw), maximal strength (bench press), reaction time, and arm crank anaerobic power test were measured. Following the intervention, the CON group exhibited no changes; however, the CS-PT, TS-PT, CS-RT, and TS-RT groups displayed significant (p = 0.001) improvements in muscular power (effect size [ES] = 1.21 [large], 1.02 [medium], 0.81 [medium], 0.64 [medium]), strength (ES = 0.40 [small], 0.43 [small], 0.62 [medium], 0.63 [medium]), reaction time (ES = - 0.71 [medium], - 0.68 [medium], - 0.83 [medium], - 0.61 [medium]), peak power (ES = 1.83 [large], 1.66 [large], 0.90 [medium], 0.67 [medium]), and mean power (ES = 0.89 [medium], 0.89 [medium], 0.57 [small], 0.59 [small]), respectively. The PT groups indicated significantly greater changes than the RT groups in both muscular (CS, p = 0.021; TS, p = 0.018) and anaerobic power (peak power: CS, p = 0.017; TS, p = 0.011; mean power: CS, p = 0.024; TS, p = 0.042) performance, while the RT groups showed greater adaptive responses than the PT groups in maximal strength (CS, p = 0.033; TS, p = 0.048). In conclusion, PT is recommended for enhancing power performance, while RT is preferred for increasing strength. When various set configurations were incorporated, no further effects were noted.

Effects of time-of-day resistance training on muscle strength, hormonal adaptations, and sleep quality during Ramadan fasting

Objectives

We investigated the timing of resistance training (RT) during Ramadan fasting (RF) on muscle strength, hormonal adaptations, and sleep quality.

Methods

Forty healthy and physically active male Muslims (age = 25.7 ± 5.6 years, body mass = 85.1 ± 17.5 kg, height = 175 ± 9 cm, BMI = 28.3 ± 5.7 kg/m2) were enrolled in this study and 37 completed pre and post-tests. Subjects were randomly allocated into two experimental groups. Group 1 (FAST, n = 20) completed an 8-week whole-body RT in the late afternoon (between 16 h and 18 h) while fasting. Group 2 (FED, n = 20) completed the similar RT protocol compared with FAST at night (between 20 h and 22 h). The following parameters were analyzed at various time-points: 2 weeks before the start of RF (T0), on the 15th day of Ramadan (T1), on the 29th day of Ramadan (T2), and 21 days after the last day of RF (T3) where both groups were in a fed state. One-repetition maximum tests (1-RM) were conducted for the squats (1-RMSQ), the deadlift (1-RMDL) and the bench press (1-RMBP). Sleep quality was assessed using the full Pittsburgh Sleep Quality Index (PSQI). Blood samples were taken to determine cortisol, testosterone and IGF-1 levels. Additionally, acute hormonal responses were evaluated before (BF), immediately after (AF), and 30 min after a RT session (AF-30 min) at T0, T1, T2, and T3.

Results

Significant group-by-time interactions were identified for 1-RMSQ (p = 0.001; effect size [ES] = 0.43) and 1-RMDL (p = 0.001; ES = 0.36). Post-hoc tests indicated significant 1-RMSQ (p = 0.03; ES = 0.12) and 1-RMDL (p = 0.04; ES = 0.21) improvements from T0-T2 for FED. Additionally, significant group-by-time interactions were observed for the chronic effects on cortisol (p = 0.03; ES = 0.27) and testosterone levels (p = 0.01; ES = 0.32). Post-hoc tests indicated significant increases of cortisol levels among FAST at T1 and T2 compared to T0 (p = 0.05; ES = 0.41, p = 0.03; ES =  0.34) and a significant increase in cortisol levels in FED at T1 (p = 0.05; ES = 0.29) and T2 (p = 0.04; ES = 0.25). However, the observed increase was lower compared to FAST. Post-hoc tests also indicated significant increases of testosterone only among FED at T2 (p = 0.04; ES = 0.31). A significant group-by-time interaction was found for the acute effect of exercise on cortisol level (p = 0.04; ES = 0.34). The cortisol level immediately after RT was higher in FAST only at T1 (p = 0.03; ES = 0.39) and T2 (p = 0.05; ES = 0.22) compared with T0. No significant group-by-time interactions were identified for sleep quality (p = 0.07; ES = 0.43).

Conclusion

Muslims can safely practice RT during RF. However, training in a fed state during Ramadan might be more effective than during fasted state for the enhancement of maximal strength with better hormonal responses observed.

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

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 (ηp²) 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).

Constitutional thinness might be characterized by physiologically adapted and not impaired muscle function and architecture: new results from the NUTRILEAN study

PURPOSE

While muscle mass and skeletal muscle fibers phenotype have been shown atypical in constitutional thinness (CT), force production capacities and its architectural determinants have never been explored. The present study compared muscle functionality and architecture between participants with CT and their normal-weight (NW) counterparts.

METHODS

Anthropometry, body composition (Dual-X-ray Absorptiometry), physical activity/sedentary behavior (ActiGraph wGT3X-BT), ultrasound recording of the Vastus Lateralis (2D-ultrasound system), and functional capacities at maximal isometric and isokinetic voluntary contractions (MVCISO and MVCCON) during knee extension (isokinetic dynamometer chair Biodex) have been measured in 18 women with CT (body mass index < 17.5 kg/m2) and 17 NW women.

RESULTS

A lower fat-free mass (ES: -1.94, 95%CI: -2.76 to -1.11, p < 0.001), a higher sedentary time, and a trend for a lower time spent at low-intensity physical activity, were observed in CT vs NW participants. While absolute MVCISO, MVCCON, rate of torque development (RTD), and torque work were all markedly lower in CT, these differences disappeared when normalized to body or muscle mass. Muscle thickness and fascicle length were found lower in CT (ES: -1.29, 95%CI: -2.03 to -0.52, p < 0.001; and ES: -0.87, 95%CI: -1.58 to -0.15, p = 0.02, respectively), while pennation angle was found similar.

CONCLUSION

Despite lower absolute strength capacities observed in CT, present findings support the hypothesis of physiological adaptations to the low body and muscle mass than to some intrinsic contractile impairments. These results call for further studies exploring hypertrophy-targeted strategies in the management of CT.

Synergistic Effects of Concurrent Aerobic and Strength Training on Fitness in Children and Adolescents: A Multivariate and Network Meta-Analysis

The decline in fitness levels among children and adolescents underscores the urgent need for effective exercise interventions. Aerobic endurance training (ET) and resistance training (RT) are vital for physical development in this demographic. This study employs multivariate and network meta-analysis (NMA) to assess the impact of concurrent training (CT), which integrates both ET and RT, on youth physical fitness. The objective is to identify the distinct advantages of CT over either ET or RT alone, emphasizing demographic and training-specific variables. A systematic literature review of publications from 1980 onward was conducted through ISI Web of Science, PubMed/MEDLINE, and SPORTDiscus databases, adhering to the PICOS criteria for study selection. Data were analyzed using univariate, multivariate, and network meta-analyses in Stata 17.0, focusing on cardiorespiratory fitness and muscular strength. The methodological quality and risk of bias were evaluated using the PEDro scale and Egger's test, along with sensitivity analyses and meta-regression to explore heterogeneity and publication bias. This analysis included 36 studies with 2658 participants (mean age: 14.32 ± 2.29 years) from an initial 11 074 publications, indicating low bias risk (PEDro scores ≥ 6). Univariate meta-analysis showed no significant differences in maximal oxygen uptake (VO2max) between CT and ET (standardized mean difference [SMD] = 0.01; 95% confidence interval [CI]: -0.23 to 0.25; p = 0.93). In contrast, CT significantly improved countermovement jump (CMJ) compared to RT alone (SMD = 0.19; 95% CI: 0.01-0.36; p = 0.04). Multivariate analysis confirmed notable enhancements in endurance and explosiveness for CT compared to ET or RT. NMA indicated significant improvements in lower limb strength, CMJ, and VO2max across interventions compared to controls, with the consecutive resistance training followed by ET (CRE) group yielding the most significant CMJ improvement (SMD = 0.27; 95% CI: 0.07-0.47). Isolated RT showed the highest lower limb strength improvement (SUCRA score 80.1%), while CRE excelled in CMJ advancements (SUCRA score 93.4%), and the CRED group (alternating ET and RT) led in VO2max improvements (SUCRA score 81.6%). Furthermore, high-intensity interval training (HIIT) significantly enhanced VO2max compared to team sports. This meta-analysis emphasizes the effectiveness of CT in improving muscle power and VO2max in children and adolescents, surpassing isolated ET or RT, and advocates for integrating ET and RT to optimize physical performance. Future research should explore the mechanisms underlying these enhancements. Trial Registration: PROSPERO registration number CRD42022368452.

Acute Effect of Fixed vs. Self-Selected Rest Interval Between Sets on Physiological and Performance-Related Responses

Background: Although the comparison between self-managed rest and fixed rest periods in subjects experienced in lower-limb strength training has been investigated, the results remain unclear due to controversies among some studies. Therefore, the present study aimed to analyze the role of self-managed rest versus fixed rest in athletic performance, mean propulsive velocity, velocity loss, muscle oxygen saturation, and rest time in trained subjects; Methods: Thirteen subjects with a minimum of one year of training experience (age (years): 26.31 ± 3.84; height (cm): 175.46 ± 5.61; weight (kg): 79.24 ± 6.83) were randomly assigned to two groups (self-selected rest group [SR] = 7 and fixed rest group [FR] = 6). The subjects underwent a session for evaluation (one maximum repetition (1RM) estimation, familiarization, and data collection) and another day for a traditional strength training session for the back squat, consisting of five sets of four repetitions at 80% of 1RM. One group took a fixed 2 min break, while the other group managed their breaks autonomously (resuming when they felt ready to perform the next set at maximum velocity). Mean propulsive velocity (MPV) was monitored using a linear position transducer, and muscle oxygen saturation (SmO2) was measured with a near-infrared spectroscopy device; Results: Significant differences between the groups were found for the rest time between the first and second sets (SR 97.29 ± 23.70 seg vs. FR 120 ± 0.00 seg). However, no differences were found for MPV, velocity loss, or SmO2; Conclusions: Given the similarities in performance and physiological outcomes between fixed and self-selected rest conditions, both can be used equally depending on the preferences and training goals of coaches and athletes.

The effectiveness of the Copenhagen adduction exercise on improving eccentric hip adduction strength among soccer players with groin injury: a randomized controlled trial

INTRODUCTION

Groin injuries are common in soccer players and often involve adductor muscle strains. The Copenhagen Adduction Exercise (CAE) is a targeted intervention whose effectiveness in rehabilitation for these injuries warrants investigation.

OBJECTIVE

To investigate the impact of a rehabilitation program, which includes the CAE, on eccentric hip adduction (EHAD) strength, hip joint range of motion (ROM), self-reported disability, and pain among soccer players with adductor-related groin pain. It was hypothesized that the addition of CAE to the rehabilitation program would yield greater improvements.

METHODS

Employing a randomized controlled trial with a two-group parallel design, thirty male soccer players with a mean age of 26.4 ± 3.9 years were randomized into an intervention group (IG) including CAE (n = 15) and a control group (CG) without CAE (n = 15), based on a power analysis to ensure 80% power to detect significant differences. Both groups engaged in their respective rehabilitation programs twice a week for eight weeks. The primary outcome measured was EHAD strength, while secondary outcomes included hip joint ROM, self-reported disability measured by the Copenhagen Hip and Groin Outcome Score (HAGOS), and pain levels.

RESULTS

Significant improvements within groups were observed across all measures (p < 0.001). The IG demonstrated a greater increase in EHAD strength (Mean Difference [MD] = 0.49 Nm/kg, 95% Confidence Interval [CI] [0.31, 0.66]), a more pronounced reduction in pain (MD = -1.60, 95% CI [-2.18, -1.02]), and betterment in all HAGOS subscale scores compared to the CG. There were no significant between-group differences in hip joint ROM.

CONCLUSION

Incorporating the CAE into rehabilitation programs significantly improves EHAD strength, decreases pain scores, and reduces self-reported disability in soccer players with adductor-related groin pain.

REGISTRATION

ClinicalTrials.gov identifier: NCT05589623.

Local, proximal, and distal effects of resistance training with blood flow restriction on strength and size of upper limb muscles in healthy individuals: A systematic review

INTRODUCTION

Resistance training with blood flow restriction (BFR) can promote gains in muscle strength and size using low-load protocols.

OBJECTIVE

To gather the evidence on local, proximal, and distal effects of resistance training with BFR on the strength and size of upper limb muscles in healthy individuals.

METHODS

Searches were performed in CENTRAL, PEDro, MEDLINE, SciELO, SCOPUS, and Science Direct databases from inception to March 2023. Clinical trials that compared the effects of resistance training with and without BFR (≥4 weeks) on the strength and size of upper limb muscles in healthy individuals were included. Data related to studies' participants, BFR techniques, resistance training protocols, outcomes and assessment measures, and main results were collected. The risk of bias and quality of evidence was assessed using the Cochrane Risk of Bias Analysis Tool and the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach, respectively.

RESULTS

Twenty-three studies with a low-high risk of bias and a very-low-to-high quality were included in this review. In general, findings suggest that either high- or low-load resistance training with BFR provided greater local, proximal, and/or distal gains in muscle size and strength compared to resistance training without BFR.

CONCLUSIONS

Resistance training with BFR can increase the strength and size of upper limb muscles in healthy individuals. Caution must be taken when interpreting and generalizing the results gathered in this review high heterogeneity of the included studies' methods.

MicroRNAs and their Modulatory Effect on the Hallmarks of Osteosarcopenia

PURPOSE OF THE REVIEW

Osteosarcopenia is a geriatric syndrome associated with disability and mortality. This review summarizes the key microRNAs that regulate the hallmarks of sarcopenia and osteoporosis. Our objective was to identify components similarly regulated in the pathology and have therapeutic potential by influencing crucial cellular processes in both bone and skeletal muscle.

RECENT FINDINGS

The simultaneous decline in bone and muscle in osteosarcopenia involves a complex crosstalk between these tissues. Recent studies have uncovered several key mechanisms underlying this condition, including the disruption of cellular signaling pathways that regulate bone remodeling and muscle function and regeneration. Accordingly, emerging evidence reveals that dysregulation of microRNAs plays a significant role in the development of each of these hallmarks of osteosarcopenia. Although the recent recognition of osteosarcopenia as a single diagnosis of bone and muscle deterioration has provided new insights into the mechanisms of these underlying age-related diseases, several knowledge gaps have emerged, and a deeper understanding of the role of common microRNAs is still required. In this study, we summarize current evidence on the roles of microRNAs in the pathogenesis of osteosarcopenia and identify potential microRNA targets for treating this condition. Among these, microRNAs-29b and -128 are upregulated in the disease and exert adverse effects by inhibiting IGF-1 and SIRT1, making them potential targets for developing inhibitors of their activity. MicroRNA-21 is closely associated with the occurrence of muscle and bone loss. Conversely, microRNA-199b is downregulated in the disease, and its reduced activity may be related to increased myostatin and GSK3β activity, presenting it as a target for developing analogues that restore its function. Finally, microRNA-672 stands out for its ability to protect skeletal muscle and bone when expressed in the disease, highlighting its potential as a possible therapy for osteosarcopenia.

Effect of two quadriceps strengthening protocols on morphological characteristics of knee vastus muscles in patients with lateral patellar compression syndrome

INTRODUCTION

The purpose of this study is to compare the effect of two types of quadriceps strengthening protocols on morphological characteristics of the knee vastus muscles in patients with lateral patellar compression syndrome.

METHODS

48 female patients were randomly divided into 3 groups: selective (16), general (17) and control (15). The selective group participated in an isokinetic knee extension training protocol at the last 30° knee extension arc with maximum leg external rotation at high speed with the aim of selectively strengthening the vastus medialis muscle. The general group participated in an exercise protocol aimed at strengthening the entire quadriceps muscle. Both these protocols lasted 8 weeks. The control group did not receive any intervention. The vastus medialis and lateralis muscles cross-sections and fibers angles were measured using an ultrasound device. The data were analyzed using repeated-measures ANOVA and dependent t tests.

RESULTS

At pre-intervention, there were no differences between groups in muscles cross-sections and fiber angles (P > 0.05), but after interventions, in selective group, the vastus medialis cross-section and fiber angle, as well as vastus medialis to vastus lateralis cross-section ratio, were significantly higher than other groups (P < 0.01). Also, compared to pre-intervention, the vastus medialis cross-section and fiber angle increased only in selective group (P = 0.001), and the vastus lateralis cross-section increased only in general group (P = 0.001).

DISCUSSION AND CONCLUSION

Use of isokinetic extension exercises targeting selectively strengthening the vastus medialis can improve the activity and involvement of this muscle-which is impaired in chronic patellofemoral joint disorders - by changing its morphology.

Optimal cut-off values of the active knee extension test for diagnosing hamstring tightness

BACKGROUND

Active knee extension (AKE) is widely used to assess hamstring length, and an 'AKE >20°' is often used as the criterion for diagnosing tightness. However, the scientific evidence for this is unclear.

OBJECTIVE

This study measured and analysed AKE according to sex in two groups with different exercise participation levels to identify the appropriateness of current criteria.

METHODS

In the supine position, 90° flexion of the hip and knee joints was performed. The maximal knee extension was measured using a goniometer. Cut-off values for diagnosing hamstring tightness were calculated in three different ways as 'mean-1SD', 'mean-2SD', and 'mean-3SD'.

RESULTS

There were significant differences in AKE between groups and between sexes. In group A, representing normal healthy adults, cut-off values defined as mean-1SD and mean-2SD were 33.5° and 19.7° in male participants and 28.0° and 15.7° in female participants, respectively. There was a weak correlation between AKE and body mass index, but not between AKE and height and between AKE and weight.

CONCLUSION

This study found that the level of exercise participation significantly affects AKE, and female participants consistently had high flexibility regardless of exercise participation. Therefore, the current cut-off value, widely used in research and clinical settings, may not be a suitable criterion for diagnosing hamstring tightness.

Sex Differences in Effects of Exercise on Physical Function in Aging: A Systematic Review with Meta-Analysis

PURPOSE

Our objective was to synthesize and determine whether there are sex differences in physical function following exercise interventions in older adults.

MATERIALS AND METHODS

A systematic search was conducted in four databases from inception to July 8th, 2023 searching for prospective trials that conducted exercise interventions in older adults and results for physical function were reported by sex. Pooled standardized mean differences (SMDs) with their 95% confidence intervals (CIs) were estimated using a randomeffects method. The Sidik-Jonkman estimator was used to calculate the variance of heterogeneity (I²).

RESULTS

A total of 19 studies involving 20,133 older adults (mean age ≥60 years, 33.7% female) were included. After exercise interventions, males reported significantly greater pre-post changes compared to females for upper body strength (SMD=-0.40, 95% CI: -0.71 to -0.09; I²=75.6%; n=8), lower body strength (SMD=-0.32, 95% CI: -0.55 to -0.10; I²=52.0%; n=11), and cardiorespiratory fitness (SMD=-0.29, 95% CI: -0.48 to -0.10; I²=89.1%; n=12). Conversely, the pooled SMDs showed a significant effect favoring females for motor fitness (SMD=0.21, 95% CI: 0.03 to 0.39; I²=0%; n=7). Limited and inconsistent results were observed for flexibility.

CONCLUSIONS

Our study suggests the existence of sex-related differences on physical function after an exercise intervention in the older population.

Long-Term Resistance Trained Human Muscles Have More Fibers, More Myofibrils, and Tighter Myofilament Packing Than Untrained

INTRODUCTION

Increases in skeletal muscle size occur in response to prolonged exposure to resistance training that is typically ascribed to increased muscle fiber size. Whether muscle fiber number also changes remains controversial, and a paucity of data exists about myofibrillar structure. This cross-sectional study compared muscle fiber and myofibril characteristics in long-term resistance-trained (LRT) versus untrained (UNT) individuals.

METHODS

The maximal anatomical cross-sectional area (ACSAmax) of the biceps brachii muscle was measured by magnetic resonance imaging in 16 LRT (5.9 ± 3.5 yr' experience) and 13 UNT males. A muscle biopsy was taken from the biceps brachii to measure muscle fiber area, myofibril area, and myosin spacing. Muscle fiber number, and myofibril number in total and per fiber were estimated by dividing ACSAmax by muscle fiber area or myofibril area, and muscle fiber area by myofibril area, respectively.

RESULTS

Compared with UNT, LRT individuals had greater ACSAmax (+70%, P < 0.001), fiber area (+29%, P = 0.028), fiber number (+34%, P = 0.013), and myofibril number per fiber (+49%, P = 0.034) and in total (+105%, P < 0.001). LRT individuals also had smaller myosin spacing (-7%, P = 0.004; i.e., greater packing density) and a tendency toward smaller myofibril area (-16%, P = 0.074). ACSAmax was positively correlated with fiber area ( r = 0.526), fiber number ( r = 0.445), and myofibril number (in total r = 0.873 and per fiber r = 0.566), and negatively correlated with myofibril area ( r = -0.456) and myosin spacing ( r = -0.382) (all P < 0.05).

CONCLUSIONS

The larger muscles of LRT individuals exhibited more fibers in cross-section and larger muscle fibers, which contained substantially more total myofibrils and more packed myofilaments than UNT participants, suggesting plasticity of muscle ultrastructure.

Effects of a 16-week High-Speed Resistance Training program on body composition in community-dwelling independent older adults: A clinical trial

BACKGROUND & AIMS

Aging frequently causes changes in body composition, such as a loss of strength and muscular mass and an increase in fat mass. Exercise training programs have been suggested as effective strategies to mitigate or prevent age-related declines in body composition. Therefore, this study examined the effects of a sixteen-week High-Speed Resistance Training (HSRT) program on body composition parameters in community-dwelling independent older adults.

METHODS

The present clinical trial included 79 older adults, who were divided into two groups: intervention group (IG, N = 40, age, 68.50 ± 3.54 years; weight, 68.65 ± 11.36 kg) and control group (CG, N = 39, age, 72.08 ± 5.89 years; weight, 67.04 ± 10.69 kg). IG performed the supervised HSRT for 16 weeks, with 3 sessions per week of 60-70min, each session of 5-6 exercises, 2-3 sets, and 6-10 reps/exercise, while CG did not perform any exercise training program. Body composition parameters were assessed using a multifrequency tetrapolar bioelectrical impedance analyzer (InBody® S10). The level of physical activity and the dietary intake were evaluated by the International Physical Activity Questionnaire (IPAQ-SF) and the Food Frequency Questionnaire, respectively. Statistical analyses were performed using the analysis of covariance (ANCOVA), and effect size (Cohen's dunbiased).

RESULTS

The analysis showed significant effects of the group factor for IG on phase angle (F(1) = 14.39, p < 0.001, η2p = 0.159). Additionally, results from Δ changes (post-minus pre-values) revealed small and medium effects in favor to IG for body cell mass (t(77) = 1.21, p = 0.230, dunb = 0.27 [-0.17, 0.71]) and phase angle (t(77) = 2.82, p = 0.006, dunb = 0.63 [0.18, 1.08]), respectively.

CONCLUSIONS

The HSRT could effectively prevent the decline in cellular health and cell integrity in older adults, as evidenced by the significant improvements in the phase angle.

REGISTRATION

Clinicaltrial.gov (ID: NCT05586087).