Surface electromyography-based assessment of upper-limb muscle strength, endurance, and muscle quality during graded handgrip tasks in healthy adults.

Background

Muscle strength, endurance, and muscle quality are important determinants of upper-limb function. Although surface electromyography (sEMG) characterizes muscle activation and fatigue, its integration with bioelectrical impedance analysis (BIA) for muscle quality assessment remains limited.

Objective

This study investigated neuromuscular responses during graded handgrip contractions and evaluated an exploratory muscle quality (MQ) index integrating sEMG and BIA measures in healthy adults.

Methods

Fifty-three healthy adults (35 males and 18 females) performed maximal voluntary contraction (MVC) followed by graded handgrip contractions at 0%, 20%, 40%, 60%, 80%, and 100% MVC. Surface EMG was recorded from the biceps brachii, triceps brachii, brachioradialis, and flexor carpi ulnaris. Root mean square (RMS) and frequency-domain features were extracted, with median frequency (fmedian) selected as the representative frequency-domain outcome for nonparametric analyses and linear mixed-effects analysis. The MQ index integrated grip strength, muscle mass, body fat, and RMS and was evaluated using Spearman correlation.

Results

RMS increased with contraction intensity, whereas fmedian increased to a peak at 60% MVC and then gradually declined with the lowest values at 100% MVC. Significant fixed effect and interaction indicated that neuromuscular responses varied by gender, muscle, contraction stage, and muscle mass. The MQ index correlated moderately with right-arm muscle mass and phase angle but weakly with the conventional muscle quality index.

Conclusion

Integrating sEMG and BIA provides complementary information on muscle activation, fatigue, and tissue characteristics beyond conventional strength-based measures, supporting assessment of upper-limb neuromuscular function and muscle quality.