Exercise-induced muscle damage: effect on circulating leukocyte and lymphocyte subsets.

The purpose of this study was to determine the effect of downhill and level running on circulating leukocyte and lymphocyte subsets and T lymphocyte activation. Using a random cross-over design, 10 runners completed two trials of 60 min of level running (0% grade; LR) and downhill running (-10% grade; DHR) at 70% of level VO2max. Blood samples were obtained preexercise and immediately postexercise (POST) and at 1.5, 12, 24, and 48 h of recovery. Creatine kinase activity peaked at 12 h of recovery from DHR and was not significantly altered following LR. The number of total T, CD16+, CD3+CD56+ cells were significantly higher POST DHR compared with LR. Leukocyte and neutrophil counts were significantly higher at 1.5 and 12 h of recovery from DHR compared with LR. The number of activated CD8+ cells (CD25+ CD8+) was significantly higher at 12 h of DHR compared to LR. Total T cells were significantly reduced at various time points during the 48 h of recovery from LR and DHR. In summary, DHR relative to LR resulted in a greater mobilization of lymphocytes (post), neutrophils (1.5-12 h of recovery) and activation of CD8+ cells at 12 h of recovery. In addition, reductions in circulating T lymphocyte subsets occurred following both conditions.