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Effects of Step Exercise on Muscle Damage and Muscle Ca2+ Content in Men and Women

Fredsted, A, Clausen, T, Overgaard, K. Effects of step exercise on muscle damage and muscle Ca2+ content in men and women. J Strength Cond Res 22: 1136-1146, 2008-Eccentric exercise often produces severe muscle damage, whereas concentric exercise of a similar load elicits a minor degree of muscle damage. The cellular events initiating muscle damage are thought to include an increase in cytosolic Ca2+. It was hypothesized that eccentric muscle activity in humans would lead to a larger degree of cell damage and increased intracellular Ca2+ accumulation in skeletal muscle than concentric activity would. Furthermore, possible differences between men and women in muscle damage were investigated following step exercise. Thirty-three healthy subjects (18 men and 15 women) participated in a 30-minute step exercise protocol involving concentric contractions with 1 leg and eccentric contractions with the other leg. Muscle Ca2+ content, maximal voluntary contraction (MVC), and muscle enzymes in the plasma were measured. In a subgroup of the subjects, T2 relaxation time was measured by magnetic resonance imaging. No significant changes were found in muscle Ca2+ content in vastus lateralis biopsy specimens in women or in men. Following step exercise, MVC decreased in both legs of both genders. The women had a significantly larger strength decrease in the eccentric leg than the men had on postexercise day 2 (p < 0.01). Plasma creatine kinase increased following step exercise, with a sevenfold higher response in women than in men on day 3 (p < 0.001). The women, but not the men, had an increase in T2 relaxation time in the eccentrically working adductor magnus muscle, peaking on day 3 (75%) (p < 0.001). In conclusion, step exercise does not lead to Ca2+ accumulation in the vastus lateralis but does induce muscle damage preferentially in the eccentrically working muscles, considerably more in women than in men. This indicates that gender-specific step training programs may be warranted to avoid excessive muscle damage.