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  • Title: Changes in knee joint angle affect torque steadiness differently in young and older individuals.
    Author: Wu R, Delahunt E, Ditroilo M, Lowery MM, Segurado R, De Vito G.
    Journal: J Electromyogr Kinesiol; 2019 Aug; 47():49-56. PubMed ID: 31121550.
    Abstract:
    PURPOSE: This study investigated the effect of knee joint angle and age on torque steadiness of knee extensors (KE) at varying submaximal isometric contractions. METHODS: 22 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. RESULTS: Age-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). CONCLUSIONS: These 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.
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