Surface EMG model of the bicep during aging: a preliminary study

Area of Science:

• Biomedical Engineering
• Muscle Physiology
• Gerontology

Background:

• Surface electromyogram (sEMG) signal characteristics, including median frequency and amplitude, decrease with age.
• These sEMG changes are linked to reduced muscle fiber count and a lower ratio of type II (fast-twitch) fibers, though the precise relationship remains unclear.

Purpose of the Study:

• To experimentally quantify age-related differences in sEMG magnitude and spectrum between younger and older adults.
• To develop and validate a computational model of muscle changes based on experimental sEMG data.

Main Methods:

• Experiments were conducted on two age groups: younger (20-28 years) and older (61-69 years).
• sEMG signals were recorded and analyzed for differences in magnitude and spectral content.
• A lifelike computational model was populated with experimental data to simulate age-related muscle changes.

Main Results:

• The computational model simulating older adults required a substantially reduced number of motor units to match experimental sEMG data compared to the younger cohort model.
• The optimal model fit for older subjects was achieved when the ratio of bicep motor units was 0.5 compared to younger subjects.
• A significant decrease in the fast fiber ratio was observed, dropping from 0.45 in younger individuals to 0.11 in older individuals.

Conclusions:

• Age-related reductions in sEMG are strongly associated with a decreased number of motor units and a diminished proportion of fast-twitch muscle fibers.
• The findings provide quantitative insights into the neuromuscular adaptations occurring with aging.