Objective. Previous studies have demonstrated that various factors alter postural stability. Our aim was to examine the effect of plantar flexor fatigue on postural stability in quiet standing.

Methods. Fifteen healthy male university students (age, 21.3 ± 1.7y; height, 1.83 ± 0.06m; weight, 81.6 ± 9.4kg) were instructed to stand on a force plate before and after calf fatiguing exercise. The sensory systems were controlled by blindfolding subjects and having them stand on a flat firm surface, without moving their head. Fatigue was achieved through repetitive weighted plantar-flexor exercise. Standing balance was assessed by using a force plate to calculate Center of Pressure (CoP) displacement.

Results. Plantar flexor fatigue led to significant (p<0.05) postural control impairments in the frontal and sagittal planes compared to non-fatigue (control). Fatigue led to significant changes in M/L (1.66 ± 0.85mm and 3.30 ± 1.24mm for control and fatigue, respectively) and A/P (4.48 ± 1.70mm and 8.89 ± 3.74 for control and fatigue, respectively) CoP variance.

Interpretation. Lower limb fatigue led to significant postural control impairments. Interestingly fatigue in the plantar flexors, primary responsible for control in A/P directions, led to significant postural sway in the M/L directions. Therefore, it is possible that other muscle groups (i.e. hip and knee flexors and extensors) are used to correct posture, as the plantar flexors are not at full functioning capacity. It can be concluded that under a sensory controlled environment, postural control is significantly impaired by lower limb fatigue, and can possibly be supported by other muscle groups.

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