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

Area of Science:

• Exercise immunology
• Human physiology
• Sports science

Background:

• Running impacts immune cell circulation and function.
• Downhill running imposes unique eccentric muscle stress compared to level running.
• Understanding these effects is crucial for athlete recovery and performance.

Purpose of the Study:

• To investigate the differential effects of downhill running (DHR) versus level running (LR) on immune cell populations and T cell activation.
• To quantify changes in leukocyte and lymphocyte subsets post-exercise and during recovery.
• To assess T lymphocyte activation markers following DHR and LR.

Main Methods:

• Randomized cross-over design with 10 runners.
• 60-minute running trials at 70% VO2max on a level (0%) and downhill (-10%) grade.
• Blood sampling pre-exercise and at multiple time points up to 48 hours post-exercise.
• Analysis of leukocyte counts, lymphocyte subsets (T cells, CD16+, CD3+CD56+), and activated CD8+ T cells (CD25+ CD8+).
• Measurement of creatine kinase activity as a marker of muscle damage.

Main Results:

• Creatine kinase peaked 12 hours post-DHR, indicating greater muscle stress.
• Higher counts of total T cells, CD16+, and CD3+CD56+ cells immediately post-DHR compared to LR.
• Elevated leukocyte and neutrophil counts at 1.5 and 12 hours post-DHR.
• Increased activated CD8+ T cells 12 hours post-DHR.
• Significant reductions in circulating T lymphocyte subsets observed during recovery from both LR and DHR.

Conclusions:

• Downhill running induces a more pronounced immune response, including greater lymphocyte mobilization and neutrophil influx, compared to level running.
• Downhill running leads to enhanced CD8+ T cell activation during recovery.
• Both running conditions result in a temporary decrease in circulating T lymphocyte subsets, highlighting the systemic immune impact of prolonged running.