Changes in antagonist muscles' coactivation in response to strength training in older women.

BACKGROUND: The purpose of this study was to assess changes in neuromuscular function of the plantarflexor and dorsiflexor muscles after 1 year of strength training of these muscles in elderly women. Twelve participants were assigned to a training (74.2 +/- 3.1 years) group and eight to a nontraining group (73.6 +/- 4.3 years).

METHODS: Isometric maximum voluntary contractions (MVC) and muscle activation based on surface electromyography (EMG) were recorded before and after the 12-month training program at six different joint angles.

RESULTS: After training (in the training group), (a) plantarflexion (PF) MVC increased on average by 14.4% (p <.05) across ankle joint angles from -20 degrees dorsiflexion (DF) to +30 degrees PF, (b) DF MVC decreased by 5.7% (p <.05), (c) PF EMG root mean square increased on average by 22.3% (p <.05), and (d) PF antagonists' coactivation increased on average by 7.5% across the tested joint angles. No changes were observed in the nontraining group.

CONCLUSIONS: The present results show a significant increase in antagonist muscle coactivation with strength training in older women. The hypothesis is put forward that with a training-induced gain in agonist muscles' torque, stabilization of the ankle joint by increasing antagonist coactivation is needed because of a changed ratio of maximal PF torque to maximal DF torque.