Complexity of Knee Extensor Torque: Effect of Aging and Contraction Intensity

Area of Science:

• Biomechanics
• Human Physiology
• Gerontology

Background:

• Knee extensor muscles are crucial for daily activities.
• Assessing torque complexity in older adults is important for understanding functional decline.
• Aging impacts neuromuscular function and force production.

Purpose of the Study:

• To investigate the effects of aging on knee extensor torque complexity.
• To determine how isometric contraction intensity influences torque complexity in young and older adults.
• To compare torque variability and complexity between age groups.

Main Methods:

• Eight young and 13 older adults performed maximal voluntary contractions (MVC) and submaximal isometric contractions (SICs) at 15%, 30%, and 40% MVC.
• Knee extensor torque signals were continuously sampled.
• Torque variability (coefficient of variation) and complexity (corrected approximate entropy, sample entropy, and normalized versions) were calculated.

Main Results:

• Younger adults produced greater isometric torque than older adults.
• Torque variability (CV) was similar between groups, except at 40% MVC where young adults had higher CV.
• Knee extensor torque complexity was reduced in older adults, but its relationship with contraction intensity was preserved.

Conclusions:

• Despite age-related decreases in neuromuscular system interactions, the organization of force control in knee extensors is preserved in older adults.
• This preservation of force control organization is evident up to submaximal contraction levels (below midrange force).
• The findings highlight a nuanced effect of aging on neuromuscular control of force production.