Motor imagery and resistance training improve strength in older adults through distinct effects on agonist-antagonist...

Age-related declines in muscle strength are partly attributable to altered neural drive and agonist-antagonist coordination. This study aimed to evaluate the effects of motor imagery training (MIT) on maximal force production and neuromuscular activation patterns in healthy older adults, with conventional strength training (CST) included as a reference intervention.

Thirty-two right-handed older adults were randomly assigned to an 8-week MIT (n = 12), CST (n = 12), or non-exercise control group (CTRL; n = 8). Twenty-seven participants completed the intervention (MIT: n = 11; CST: n = 10; CTRL: n = 6). Training was performed 5 sessions/week. Maximal voluntary isometric elbow flexion force and surface EMG activity of the biceps brachii (agonist) and triceps brachii (antagonist) were recorded pre- and post-intervention. Antagonist muscle co-activation (AMCA) and co-contraction index (CCI; antagonist-to-agonist EMG ratio) were quantified. Post-intervention values were analyzed using ANCOVA with baseline values as covariates. Exploratory within-subject correlation analyses were conducted to examine associations between changes in force and coordination metrics.

Both MIT and CST significantly increased maximal force compared with CTRL (p < 0.001), with no difference between training modalities. Both interventions significantly reduced CCI (p < 0.001), indicating improved relative agonist-antagonist coordination. In contrast, absolute antagonist muscle co-activation (AMCA) did not change significantly in either group. Exploratory analysis further revealed significantly greater post-intervention agonist EMG in both MIT and CST compared with CTRL. In addition, exploratory analyses revealed a significant negative association between changes in force and changes in CCI, whereas no significant association was observed between changes in force and AMCA.

Both MIT and CST were associated with improvements in strength and coordination efficiency in older adults. Exploratory findings further suggest that strength gains may be more closely aligned with changes in relative agonist-antagonist coordination than with changes in absolute antagonist activation. Exploratory agonist EMG analysis further provides context suggesting that increased agonist activation may contribute, at least in part, to the observed coordination changes. These findings are consistent with a contribution of neural mechanisms, although direct neurophysiological measures are needed to confirm the underlying processes. Motor imagery training may therefore represent a viable low-load strategy for neuromuscular rehabilitation in aging populations.