Force stability training decreased force variability of plantar flexor muscles without reducing postural sway in female older adults

Background: Previous studies reported a relationship between postural sway and force variability of the plantar flexor muscles (PFM), such that less force variability related to lower postural sway; however, this association does not seem to exist in older adults.

Research question: This study investigated the effect of force stability training of the PFM on force variability (FV) of these muscles and postural sway in female older adults.

Methods: Thirty female older adults were divided into three groups: TG5 (n = 10), who trained at 5% of maximum voluntary isometric contraction (MVIC) of the PFM; TG10 (n = 10), who trained at 10 % of MVIC of the PFM; and CG (n = 10) who did not perform any specific training for the PFM. Postural sway was evaluated during upright bipodal posture. Postural sway and FV of the PFM were assessed before and after the training period. Participants trained once a week for four weeks.

Results: After the training period, the FV decreased significantly for both TG5 (pre = 3.26 ± 0.83; post = 2.53 ± 0.60 N) and TG10 (pre = 3.50 ± 0.72; post = 2.85 ± 0.86 N), but the mean sway amplitude increased for both TG5 (pre = 0.017 ± 0.03; post = 0.19 ± 0.04 cm) and TG10 (pre = 0.14 ± 0.04; post = 0.16 ± 0.04 cm).

Significance: The force stability training decreased the FV of the PFM, but this decrease was insufficient to reduce postural sway in female older adults.