Publications

Purpose: The purpose of the present study was to determine whether there are sex differences in fatigue-induced changes in quiet standing and dynamic balance and establish whether changes in muscle torque and resting stiffness may explain the potential sex differences in balance responses.

Methods: Sixteen recreationally active men (age; 24.8 ± 5.0 years, height; 178.2 ± 5.6 cm, mass; 77.8 ± 13.2 kg) and 10 women (age; 21.0 ± 1.6 years, height; 167 ± 5.3 cm, mass; 61.3 ± 8.9 kg) were assessed for postural sway, Y balance test performance, isokinetic and isometric knee extensor torque and resting stiffness of the vastus lateralis (VL), gastrocnemius lateralis (GL) and Achilles tendon (AT) before and immediately after fatiguing exercise. The fatigue protocol consisted of five sets of 20-drop jumps.

Results: The fatiguing exercise elicited similar magnitude (effects size; ES) reductions in muscle torque (men; ES = 0.45–0.80, women; ES = 0.46–0.52), dynamic balance (men; ES = 0.45–0.74, women; ES = 0.47–0.79) and resting VL stiffness (men; ES = 0.46, women; ES = 0.36) in men and women (all p < 0.05). For quiet standing balance, fatigue induced an increase in postural sway metrics (ES = 0.64–1.28) and reduction in resting GL stiffness (ES = 0.40) in men (both p < 0.001) but not women (p > 0.05).

Conclusion: Fatiguing exercise, when producing a similar level of force reduction, induces similar magnitude reductions in dynamic postural control and resting VL stiffness in men and women. Distinct deteriorations in quiet standing balance in men but not women were accompanied by modifications in calf muscle stiffness following exercise-induced muscle fatigue.

Keywords: muscle fatigue, muscle damage, balance, myotonometry, muscle torque, gender

This is the first study to show similar changes in dynamic stability, muscle torque and VL stiffness of men and women after completing repeated maximal effort contractions. The only interaction between men and women was for postural sway and GL stiffness, where maximal exercise elicited an acute increase in COP metrics and a reduction in GL stiffness in men, but not women. The associations between reduced maximal torque with reductions in lower extremity reach performance and increases in postural sway in men suggest that altered ability to produce force appears to play an important role in quiet standing postural stability following maximal exercise.