Integrative Assessment of Muscle Quality Index Using sEMG, Physical Fitness Performance, and Body Composition Analysis Across Age Groups

The progressive decline of skeletal muscle mass and function, termed sarcopenia, significantly impacts mobility, independence, and quality of life in aging populations. Conventional measures such as bioelectrical impedance analysis (BIA) and grip strength primarily capture morphological aspects, providing limited insight into neuromuscular activation. This study presents an integrative approach to evaluating muscle quality by combining surface electromyography (sEMG), physical fitness assessments, and BIA-based body composition analysis. A total of 281 adults aged 20–89 years underwent seven standardized physical performance tests, including grip strength, dumbbell lifting, leg extension, chair stand, tiptoe, standing balance, and step-in-place evaluations. sEMG signals recorded from eight limb muscles were processed to extract root mean square features, which were integrated with physical and compositional parameters into a novel muscle quality index (MQi). Statistical analyses revealed significant age-related reductions in muscle quality, particularly in lower-limb performance after age 60, whereas traditional indicators showed weaker differentiation. The proposed MQi effectively captures neuromuscular degradation and provides an objective, noninvasive biomarker for assessing functional aging. This multimodal assessment enhances early detection of sarcopenia, supports individualized rehabilitation, and offers a foundation for continuous muscle health monitoring in clinical and community settings.