Introduction: Previous studies have shown that fatigue of the plantar flexor muscles and mental tasks each can lead to impaired balance. The purpose of this study is to analyze the effects of a combined increase in cognitive load and plantar flexor fatigue can have on standing balance.

Methods: Fifteen (7 males, 8 females) healthy individuals participated in one testing session. Prior to testing, participants were screened for existing balance and plantar flexor health issues via a medical history questionnaire. Participants performed a total of twelve standing balance trials, each 30 seconds in duration. These trials consisted of three control, three recall, three fatigue, and three fatigue recall trials. For each trial, participants closed their eyes and stood with their feet together on a force plate. Recall ability was evaluated based on the participant’s ability to accurately complete the reverse digit recall section of the SCAT-3. Plantar flexor fatigue was achieved by performing five repetitions of standing calf raises. Each repetition consisted of a five second eccentric contraction, a five second concentric contraction, and a five second isometric contraction. The means of the 90% radius of the center of pressure was compared to the standing baseline across all conditions.

Results:Similar significant differences were found across 90% radius and center of pressure in both medial-lateral and anterior-posterior directions. Across all three variables, the recall condition was not significantly different (p>0.05) than control standing. Both fatigue and fatigue recall conditions were significantly different (p<0.05)

Conclusion: Collectively, the data indicates that fatigue, rather than recall, had a greater effect on all measured variables of balance. This suggests that balance is a primarily muscle driven task, and not a mental task.

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