Changes in knee joint angle affect torque steadiness differently in young and older individuals

Abstract

PurposeThis study investigated the effect of knee joint angle and age on torque steadiness of knee extensors (KE) at varying submaximal isometric contractions. Methods22 young (24.0 ± 2.6 years; 11 women) and 22 older (69.4 ± 2.4 years; 10 women) healthy men and women participated. Maximal voluntary isometric contraction (MVIC) of the KE and flexors was examined at 90° and 60° of knee flexion (0° = full extension). At each angle, participants performed KE isometric contractions (20%, 50% and 80% MVIC) to evaluate torque steadiness, whereas surface EMG was concurrently acquired from the vastus lateralis and biceps femoris muscles. ResultsAge-related impairment in torque steadiness was observed only at 20% MVIC (p < 0.01). A lower level of steadiness (p < 0.001) with a higher level of agonist and antagonist activations (all p < 0.01) was observed at 90° of knee flexion in comparison with contractions at 60°. Young participants were less steady when performing contractions at 90° compared with contractions at 60° of flexion (p < 0.001), whereas there was no difference for older participants. Furthermore, a significant effect of agonist activation and antagonist co-activation on torque steadiness was observed, but only in young participants (all p < 0.05). ConclusionsThese findings suggest that: (1) knee joint angle affects torque steadiness differently in young and older individuals; (2) an age-related impairment in steadiness was only presented at the lowest considered contraction intensity; and (3) the muscle activation responses were not associated with steadiness in older individuals.