Effects of step exercise on muscle damage and muscle Ca2+ content in men and women.

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 Ca. It was hypothesized that eccentric muscle activity in humans would lead to a larger degree of cell damage and increased intracellular Ca 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 Ca 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 Ca 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 Ca 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.