On exploring muscle aging of the biceps brachii in the middle-aged population using HD-sEMG signal analysis

Although neuromuscular decline is well documented with aging, emerging evidence indicates that it may begin as early as midlife, around age 50. As this stage represents a critical window for early intervention, the present study investigated age- and sex-related differences in muscle activation using high-density surface electromyography (HD-sEMG) of the biceps brachii (BB). Physically active individuals were categorized into three age groups: young (20-30 years), middle-aged (45-55 years), and older adults (65-75 years). HD-sEMG signals were recorded during isometric contractions at 20%, 40%, and 60% of maximal voluntary contraction (MVC). Muscle activation amplitude, spatial distribution, and signal complexity were analyzed. Although strength remained similar across groups, RMS amplitude was primarily influenced by contraction level, with age-related differences emerging in an intensity-dependent manner. In men, older participants exhibited lower RMS amplitudes compared to younger men at higher contraction levels (60% MVC, p