Author(s): TRAPEZANIDOU, M., CHALATZOGLIDIS, G., DELMAS, S., CHOI, Y.J., YACOUBI, B., ARABATZI, F., CHRISTOU, E.A., Institution: ARISTOTLE UNIVERSITY OF THESSALONIKI, Country: GREECE, Abstract-ID: 1729

INTRODUCTION:
Although aging profoundly alters both neural and musculotendinous components, their distinct contributions to age-related declines in force control of plantar flexion movements remain poorly understood. The purpose of this study was to determine the neural and musculotendinous contributions to age-related declines in accuracy and variability of ballistic goal-directed plantar flexions.
METHODS:
Twenty-two young (22±2 years) and twenty-two older adults (72±6 years) were instructed to match a force target accurately (30% and 80% MVC) and as fast as possible by performing 3 sets of 10 plantar flexions. We examined neuromuscular control by quantifying peak force error (PFE), Time to Peak Force (TPF), peak force and TPF variability (CV PF, CV TPF). Muscle activity was recorded using surface EMG electrodes on Gastrocnemius Medialis and Lateralis (MG, LG), Soleus (SOL), and Tibialis Anterior (TA) muscles. Achilles tendon stiffness was also quantified to examine the peripheral contribution to force control.
RESULTS:
Older adults exhibited longer TPF, greater PFE, as well as greater CV PF and CV TPF than young adults. In addition, they exhibited altered activation and different coordination of the agonist and antagonist muscles. Age-related increases in TPF, CV PF and CV TPF were largely predicted by greater LG time to peak EMG and its variability, as well as by greater antagonistic (TA-MG peak delay) and synergistic (LG-MG and SOL-MG overlay) coactivation. The CV PF was also predicted by Tibialis Anterior EMG area variability. Achilles tendon stiffness did not differ between the two age groups.
CONCLUSION:
These findings suggest that age-related impairments in force control of ballistic, goal-directed plantar flexion are primarily driven by changes in neural mechanisms and altered motor planning, rather than by structural or functional changes in tendon properties. Consequently, interventions targeting neural coordination and motor control strategies may be more effective than those focusing exclusively on peripheral tissue properties.