The difficulty of postural tasks amplifies the effects of fatigue on postural stability.

Purpose: It was supposed that the difficulty of postural tasks accentuates the effects of fatigue on postural stability. The aim of this work was to compare the effects of fatiguing running on three different postural conditions presenting different levels of difficulty: a standing still position with the eyes open (EO condition), a standing still position with the eyes closed (EC condition) and a shooting position with the eyes open (SP condition). The SP condition required a rifle to be held horizontally with the arms and a standing posture with the non-dominant foot ahead of the dominant foot.

Methods: Thirty-two male soldiers 32.2 ± 3.8 years old completed a maximal incremental protocol on a treadmill by running until they reached a state of fatigue. The three postural conditions were evaluated in a randomized order before and after the fatiguing exercise with the use of a force platform which recorded the displacements of the centre of foot pressure.

Results: Following the fatiguing running exercise, postural stability was affected to a greater extent in the SP condition than in the EO condition and the EC condition.

Conclusion: The requirements of the SP condition modify the entire postural organization and this challenges balance control to a greater extent than when in EO and EC standing still positions, following fatiguing exercise. The difficulty of postural tasks thus amplifies the effects of fatigue on postural stability.