ObjectiveTo investigate the association of physical activity and balance ability with disability, and to further examine the mediating role of balance ability in the relationship between physical activity and disability. MethodsBased on data from 2021 to 2023 National Health and Nutrition Examination Survey (NHANES) cycle, a multivariable Logistic regression model was constructed to evaluate the independent association of physical activity and balance ability with disability, with covariates adjusted in four steps. An interaction model was further developed to assess the multiplicative interaction between physical activity and balance ability. Mediation analysis was performed using the Baron and Kenny three-step approach to examine the mediating role of balance ability, and the proportion of the mediation effect was calculated. The significance of the mediation effect was assessed using the Delta method, and robustness was verified through the Bootstrap method with a fixed random seed. Multiple sensitivity analyses were conducted to ensure the stability of the results. ResultsA total of 3 902 participants were included, with a prevalence of disability of 17.7%. Multivariable regression analysis showed that, after adjusting for all covariates, both light-intensity physical activity (LIPA) (OR = 0.489, 95%CI 0.380 to 0.629, P < 0.001) and high-intensity physical activity (HIPA) (OR = 0.493, 95%CI 0.371 to 0.656, P < 0.001) were significantly associated with a reduced risk of disability, whereas impaired balance ability was significantly associated with an increased risk (OR = 1.579, 95%CI 1.266 to 1.970, P < 0.001). The interaction effect analysis showed that the interaction between physical activity and balance ability were not significant (P > 0.05), however, the main effect of LIPA remained robust (β = -0.597, SE = 0.221, OR = 0.550, P = 0.007), while impaired balance ability was significantly associated with an increased risk of disability (β = 0.577, SE = 0.231, OR = 1.780, P = 0.012). The mediation analysis further indicated that balance ability played a robust mediating role in the association between LIPA and disability, with a mediation proportion of 21.1%. The indirect effect (a × b) was statistically significant (P < 0.001), and the 95% confidence intervals derived from the bootstrap method did not include zero. ConclusionPhysical activity and balance ability are significantly associated with disability, and balance ability may mediate the relationship between physical activity and disability, highlighting its potential value in disability risk assessment and intervention strategies.

OBJECTIVE:A great deal of evidence indicates that regular exercise can improve the health status of elderly individuals,including reducing overall and abdominal fat levels,increasing muscle mass and bone mineral density of the limbs,thereby preventing or delaying the onset of sarcopenia and its comorbidities.This study aims to determine the most reliable type,duration,and intensity of exercise interventions through meta-analysis to prevent,delay,and alleviate sarcopenia and its comorbidities in elderly individuals.METHODS:Randomized controlled trials examining the effects of exercise interventions on elderly individuals with sarcopenia and its comorbidities were searched in the PubMed,Embase,Web of Science,Cochrane Library,CNKI,and WanFang databases.The Cochrane Risk of Bias Tool was used to assess the quality of the included studies,and RevMan 5.3 software was employed for meta-analysis.Subgroup analyses were conducted to explore the effects of different exercise intervention protocols on various outcome measures.In addition,Stata 16.0 software was used to perform sensitivity analysis to assess the stability of the results,and funnel plots and Egger's test were employed to evaluate publication bias,ensuring the comprehensiveness and reliability of the results.RESULTS:(1)Sixteen studies involving 861 patients with sarcopenia and its comorbidities were included.(2)The meta-analysis results indicated that,compared with the control group,exercise significantly improved grip strength,knee muscle strength,appendicular skeletal muscle mass,skeletal muscle index,Timed Up and Go test results,gait speed,and insulin-like growth factor 1 levels(P＜0.05).However,the effect of exercise intervention on the sit-to-stand test was not significantly improved(P＞0.05).(3)Based on the results of subgroup analysis,it is recommended that elderly patients with sarcopenia and its comorbidities engage in exercise at least three times per week,with each session lasting no more than 30 minutes or exceeding 45 minutes,for at least 12 weeks.The exercise protocol should be flexibly adjusted according to the patient's health status and individual needs.CONCLUSION:Exercise interventions significantly improve muscle mass,muscle strength,physical function,and insulin-like growth factor 1 levels in elderly individuals with sarcopenia and its comorbidities,thereby enhancing their quality of life.However,further research is needed to validate these findings and optimize specific intervention protocols.

OBJECTIVE:A great deal of evidence indicates that regular exercise can improve the health status of elderly individuals,including reducing overall and abdominal fat levels,increasing muscle mass and bone mineral density of the limbs,thereby preventing or delaying the onset of sarcopenia and its comorbidities.This study aims to determine the most reliable type,duration,and intensity of exercise interventions through meta-analysis to prevent,delay,and alleviate sarcopenia and its comorbidities in elderly individuals.METHODS:Randomized controlled trials examining the effects of exercise interventions on elderly individuals with sarcopenia and its comorbidities were searched in the PubMed,Embase,Web of Science,Cochrane Library,CNKI,and WanFang databases.The Cochrane Risk of Bias Tool was used to assess the quality of the included studies,and RevMan 5.3 software was employed for meta-analysis.Subgroup analyses were conducted to explore the effects of different exercise intervention protocols on various outcome measures.In addition,Stata 16.0 software was used to perform sensitivity analysis to assess the stability of the results,and funnel plots and Egger's test were employed to evaluate publication bias,ensuring the comprehensiveness and reliability of the results.RESULTS:(1)Sixteen studies involving 861 patients with sarcopenia and its comorbidities were included.(2)The meta-analysis results indicated that,compared with the control group,exercise significantly improved grip strength,knee muscle strength,appendicular skeletal muscle mass,skeletal muscle index,Timed Up and Go test results,gait speed,and insulin-like growth factor 1 levels(P＜0.05).However,the effect of exercise intervention on the sit-to-stand test was not significantly improved(P＞0.05).(3)Based on the results of subgroup analysis,it is recommended that elderly patients with sarcopenia and its comorbidities engage in exercise at least three times per week,with each session lasting no more than 30 minutes or exceeding 45 minutes,for at least 12 weeks.The exercise protocol should be flexibly adjusted according to the patient's health status and individual needs.CONCLUSION:Exercise interventions significantly improve muscle mass,muscle strength,physical function,and insulin-like growth factor 1 levels in elderly individuals with sarcopenia and its comorbidities,thereby enhancing their quality of life.However,further research is needed to validate these findings and optimize specific intervention protocols.

OBJECTIVE:To explore the efficacy of different exercise regimens to reduce fall risks in older adults.METHODS:PubMed,Embase,Web of Science,The Cochrane Library,WanFang,and CNKI were searched for studies about exercise interventions on fall risk in healthy older adult individuals at the age of 60 years and above.The search timeframe should cover from the inception of each database to July 2023.Quality assessment and risk-of-bias were assessed using the Cochrane risk of bias tool.Meta-analysis,subgroup analysis,sensitivity analysis,and publication bias were conducted using Review Manager 5.3 and Stata 16.0.RESULTS:A total of 45 papers containing 54 studies with 3 074 participants were included in the analysis.Overall,exercise intervention can improve the interventional effects on balance(the unipedal stance test with eyes open,functional reach,Timed"Up & Go",and Berg balance scale),lower limb muscle strength(30-second chair-stand test,Five-Times Sit-To-Stand Test,and Short Physical Performance Battery),and fall-efficacy(Falls Efficacy Scale-International),leading to reduced fall risk(P＜0.05).The Meta-analysis results revealed a dosage effect of different exercise regimens to reduce fall risk in the elderly.Mind-body exercise could efficiently increase scores of the unipedal stance test[mean difference(MD)=6.81,95％confidence interval(CI)(2.17,11.44),P＜0.01];resistance exercise could efficiently increase the scores of the Timed"Up & Go"[MD=-3.12,95％CI(-5.72,-0.52),P＜0.05]and the 30-second chair-stand test[MD=1.22,95％CI(0.37,2.08),P＜0.01];and multicomponent physical activity could efficiently increase the scores of functional reach[MD=4.50,95％CI(2.58,6.42),P＜0.01],Berg Balance Scale[MD=1.05,95％CI(0.39,1.71),P＜0.01],Five-Times Sit-To-stand Test[MD=-3.15,95％CI(-4.80,-1.50),P＜0.01],Short Physical Performance Battery[MD=0.55,95％CI(0.37,0.74),P＜0.01],and Falls Efficacy Scale-International[MD=-0.41,95％CI(0.69,-0.13),P＜0.01].Conclusion:Exercise interventions can effectively improve balance,enhance limb strength and functional ability,and reduce fear of falling,and lower the risk of falls in older adults.The components of different intervention programs(such as type of exercise,duration,frequency,and session length)have varying dose-response relationships with the results of fall risk screening tests in older adults.

Objective To develop a three-compartment kinetic fatigue model for the isometric muscle endurance of the hip,knee,and ankle joints at 50％IPT(isometric peak torque),so as to provide a theoretical basis for simulation-based assessments and load evaluations in biomechanics and sports science.Methods The IPT of the hip,knee,and ankle joints was measured in 40 male university students.Isometric endurance tests were then performed on all three joints at 50％IPT until exhaustion.Electromyography data and endurance time(ET)of major lower limb muscles were collected concurrently.The differences between ETs predicted by models based on previously recommended F and R parameters and actual ETs were analyzed.Subsequently,experimental ETs were used in a grid search to optimize Fand R parameters,allowing for the development of an accurate three-compartment kinetic model.Results The ET of the hip and ankle joints was significantly longer than that of the knee joint(P＜0.001).Models using previously recommended Fand R parameters overestimated ET,with significantly higher predicted values than experimentally measured ET(P＜0.001),as well as elevated root mean squared error(RMSE)and mean relatvie error(MRE)values.The grid search successfully identified Fand R parameters for the three-compartment model in isometric endurance tests of lower limb joints,with no statistical difference between model-predicted ET and experimental ET(P＞0.05).Conclusions The developed model in this study can serve as an indirect measurement tool for evaluating load in similar activities.

Objective:To propose a functional method for locating the shoulder joint center of rotation aimed at rapid estimation of the upper limb reachable domain envelope, thereby informing ergonomic design and task optimization.Methods:In March 2024, shoulder kinematics during gait were recorded from ten adults using a three-dimensional motion-capture system. Assuming the existence of a point near the glenohumeral joint that maintains a fixed spatial relationship to the humerus and the acromion, we estimated both static and dynamic centers of rotation. Localization accuracy was quantified by the standard deviation of distance residuals to upper-arm markers. Upper-limb joint angles and anthropometric parameters were modeled via regression; combined with maximal joint ranges of motion, these were used to infer the reachable domain envelope.Results:The static center of rotation was located approximately twenty-two millimeters medial to the acromial landmark in the coronal plane and thirty-seven millimeters inferior to it. The standard deviation of the residuals for the distances from the dynamic shoulder joint center of rotation to upper-arm markers averaged 1.02 mm, which was 47.42% lower than that of the static center of rotation and 66.56% lower than that of the acromion. Moreover, the trajectory of this dynamic center showed a strong correlation with upper-limb joint angles ( R2>0.7) . Conclusion:The proposed method enables rapid and accurate estimation of the upper limb reachable domain envelope to support ergonomic design and may help reduce the risk of work-related musculoskeletal disorders.

Objective:To propose a functional method for locating the shoulder joint center of rotation aimed at rapid estimation of the upper limb reachable domain envelope, thereby informing ergonomic design and task optimization.Methods:In March 2024, shoulder kinematics during gait were recorded from ten adults using a three-dimensional motion-capture system. Assuming the existence of a point near the glenohumeral joint that maintains a fixed spatial relationship to the humerus and the acromion, we estimated both static and dynamic centers of rotation. Localization accuracy was quantified by the standard deviation of distance residuals to upper-arm markers. Upper-limb joint angles and anthropometric parameters were modeled via regression; combined with maximal joint ranges of motion, these were used to infer the reachable domain envelope.Results:The static center of rotation was located approximately twenty-two millimeters medial to the acromial landmark in the coronal plane and thirty-seven millimeters inferior to it. The standard deviation of the residuals for the distances from the dynamic shoulder joint center of rotation to upper-arm markers averaged 1.02 mm, which was 47.42% lower than that of the static center of rotation and 66.56% lower than that of the acromion. Moreover, the trajectory of this dynamic center showed a strong correlation with upper-limb joint angles ( R2>0.7) . Conclusion:The proposed method enables rapid and accurate estimation of the upper limb reachable domain envelope to support ergonomic design and may help reduce the risk of work-related musculoskeletal disorders.

BACKGROUND:Surface electromyography has been extensively utilized for monitoring muscle fatigue. However,traditional electromyographic metrics typically focus on individual muscles and fail to assess the variations in a muscle group during the fatigue process. OBJECTIVE:To establish a muscle functional network to extract complex network parameters and investigate the topological property changes of the muscle functional network under different levels of fatigue,aiming to provide theoretical and methodological foundations for fatigue monitoring and prevention. METHODS:Eleven participants performed single-leg leg press exercise at 50％ of one-repetition maximum until exhaustion. Simultaneously,electromyographic signals of seven muscles (rectus femoris,vastus lateralis,vastus medialis,biceps femoris,tibialis anterior,lateral gastrocnemius,and medial gastrocnemius),electrocardiographic signals,and Borg CR-10 scale scores were collected. The Borg CR-10 scale was used to categorize three fatigue stages:mild,moderate,and severe. Heart rate and heart rate variability were calculated to validate the effective division of fatigue stages. Using the coherence of muscle signals,a muscle functional network was constructed with the seven muscles as nodes,and four complex network parameters (clustering coefficient,average weighted degree,global efficiency,and eigenvector centrality) were extracted. Additionally,four electromyographic indices (root mean square,median frequency,instantaneous mean frequency,and co-activation ratio) were extracted and compared under the three levels of fatigue. RESULTS AND CONCLUSION:(1) Differences in heart rate and heart rate variability were observed across three fatigue stages,indicating the effectiveness of fatigue stage delineation. (2) Electromyographic indicators for different muscles under three levels of fatigue:root mean square and co-activation ratio showed no differences;however,median frequency exhibited robust fatigue trends in vastus lateralis,vastus medialis,and biceps femoris,while instantaneous mean frequency demonstrated robust fatigue trends in rectus femoris,vastus lateralis,vastus medialis,and biceps femoris. Instantaneous mean frequency outperformed median frequency and root mean square,yet all three indicators showed robust trends only for the major working muscle groups,unaffected by fatigue factors,unlike the co-activation ratio. (3) The connectivity strength between vastus lateralis and vastus medialis,vastus lateralis and biceps femoris,vastus lateralis and gastrocnemius medialis,and vastus medialis and biceps femoris gradually increased,showing significant differences in average weighted degree,clustering coefficient,and global efficiency post-fatigue,significantly correlated with fatigue levels. To conclude,changes in connectivity strength reflect the synergy and complementarity among muscles during fatigue. Clustering coefficient,average weighted degree,and global efficiency serve as fatigue markers reflecting overall muscle changes.

OBJECTIVE:To explore the efficacy of different exercise regimens to reduce fall risks in older adults.METHODS:PubMed,Embase,Web of Science,The Cochrane Library,WanFang,and CNKI were searched for studies about exercise interventions on fall risk in healthy older adult individuals at the age of 60 years and above.The search timeframe should cover from the inception of each database to July 2023.Quality assessment and risk-of-bias were assessed using the Cochrane risk of bias tool.Meta-analysis,subgroup analysis,sensitivity analysis,and publication bias were conducted using Review Manager 5.3 and Stata 16.0.RESULTS:A total of 45 papers containing 54 studies with 3 074 participants were included in the analysis.Overall,exercise intervention can improve the interventional effects on balance(the unipedal stance test with eyes open,functional reach,Timed"Up & Go",and Berg balance scale),lower limb muscle strength(30-second chair-stand test,Five-Times Sit-To-Stand Test,and Short Physical Performance Battery),and fall-efficacy(Falls Efficacy Scale-International),leading to reduced fall risk(P＜0.05).The Meta-analysis results revealed a dosage effect of different exercise regimens to reduce fall risk in the elderly.Mind-body exercise could efficiently increase scores of the unipedal stance test[mean difference(MD)=6.81,95％confidence interval(CI)(2.17,11.44),P＜0.01];resistance exercise could efficiently increase the scores of the Timed"Up & Go"[MD=-3.12,95％CI(-5.72,-0.52),P＜0.05]and the 30-second chair-stand test[MD=1.22,95％CI(0.37,2.08),P＜0.01];and multicomponent physical activity could efficiently increase the scores of functional reach[MD=4.50,95％CI(2.58,6.42),P＜0.01],Berg Balance Scale[MD=1.05,95％CI(0.39,1.71),P＜0.01],Five-Times Sit-To-stand Test[MD=-3.15,95％CI(-4.80,-1.50),P＜0.01],Short Physical Performance Battery[MD=0.55,95％CI(0.37,0.74),P＜0.01],and Falls Efficacy Scale-International[MD=-0.41,95％CI(0.69,-0.13),P＜0.01].Conclusion:Exercise interventions can effectively improve balance,enhance limb strength and functional ability,and reduce fear of falling,and lower the risk of falls in older adults.The components of different intervention programs(such as type of exercise,duration,frequency,and session length)have varying dose-response relationships with the results of fall risk screening tests in older adults.

Objective To develop a three-compartment kinetic fatigue model for the isometric muscle endurance of the hip,knee,and ankle joints at 50％IPT(isometric peak torque),so as to provide a theoretical basis for simulation-based assessments and load evaluations in biomechanics and sports science.Methods The IPT of the hip,knee,and ankle joints was measured in 40 male university students.Isometric endurance tests were then performed on all three joints at 50％IPT until exhaustion.Electromyography data and endurance time(ET)of major lower limb muscles were collected concurrently.The differences between ETs predicted by models based on previously recommended F and R parameters and actual ETs were analyzed.Subsequently,experimental ETs were used in a grid search to optimize Fand R parameters,allowing for the development of an accurate three-compartment kinetic model.Results The ET of the hip and ankle joints was significantly longer than that of the knee joint(P＜0.001).Models using previously recommended Fand R parameters overestimated ET,with significantly higher predicted values than experimentally measured ET(P＜0.001),as well as elevated root mean squared error(RMSE)and mean relatvie error(MRE)values.The grid search successfully identified Fand R parameters for the three-compartment model in isometric endurance tests of lower limb joints,with no statistical difference between model-predicted ET and experimental ET(P＞0.05).Conclusions The developed model in this study can serve as an indirect measurement tool for evaluating load in similar activities.