Characteristics of standing postural sway without vision depend on the action and duration of stretched ankle muscles.

INTRODUCTION

In the literature, the impact of stretching on postural sway remains unclear. Potential differences across studies involve stretching different muscle groups or stretching muscle groups for different durations, which may alter proprioception abilities and postural sway. We questioned whether flexibility imbalances from short-term stretching of plantar flexors would increase postural sway and proprioception compared to short-term stretching of dorsiflexors and plantar flexors and whether postural sway and proprioception would increase with increased short-term stretch durations.

METHODS

We tested whether stretching opposing ankle muscles (opposed-plantar flexors and dorsiflexors) or non-opposing muscles (non-opposed-plantar flexors) for various times (0 s, 15 s, 30 s, 45 s) could influence standing sway and/or proprioception. Young adults received 2-4 bouts of ankle stretches to discomfort before performing static stance (participants stood still with eyes closed for 45 s on a force plate) and ankle proprioception (participants actively matched remembered ankle angles, measured with a goniometer) tasks after 30 s of opposed versus non-opposed stretching (Experiment 1 A) or various stretch times for non-opposed (Experiment 1B) and opposed (Experiment 2).

RESULTS

Results revealed worse performance, thus increased variability of medio-lateral (ML) center of pressure (CoP) and lower ML CoP sample entropy, indicating less automation of sway, after opposed stretching compared to no stretch and/or non-opposed (Experiment 1 A) as well as increased ML CoP displacement and variability of ML CoP and lower ML CoP sample entropy after 45 s of opposed stretches compared to no stretch (Experiment 2). Stretching did not significantly influence proprioception; however, proprioception error negatively correlated with variability of ML CoP and ML CoP displacement.

DISCUSSION

The better ability to actively reproduce ankle positioning associates with a better internal sense of position and encourages an internal focus on movement, known to increase postural sway. Care should be taken with stretched-induced hypermobility in a balance-challenged environment like that with eyes closed.