Effect of exercise intensity on exercise-induced lymphocyte apoptosis.

Because lymphocyte apoptosis is significantly elevated immediately following high-intensity exercise in humans, it seems intuitive that the cell death process must be initiated at some point during the task. This study was designed to determine whether exercise-induced lymphocyte apoptosis occurs at a threshold level of intensity, or exists only following maximal or near-maximal exercise intensities. Fourteen untrained subjects completed a discontinuous, incremental treadmill test to exhaustion (.VO(2max)). Blood for films was sampled before the test, immediately after each work stage, and for 1-h postexercise. Blood smears were stained with May-Grünwald Giemsa and lymphocytes were evaluated for characteristic features of apoptosis. The apoptotic index (AI) during exercise at 38 % .VO(2max) was similar to pre-exercise but significantly elevated at an intensity approximating 61 % .VO(2max) (p < 0.0001). Significant increases in apoptosis were noted with additional elevations in exercise intensity (i.e., 76 %, 89 %, and 100 %, p < 0.0001). Following 20 min of recovery, AI was significantly lower than values obtained immediately postexercise (p < 0.0001). Forty minutes of recovery resulted in a further significant decrease (p < 0.0001), and by 1-h postexercise, AI was similar to pre-exercise values. Results indicate that the exercise intensity threshold for inducing an increase in lymphocyte apoptosis occurs between 40 and 60 % .VO(2max). In addition, since values return to baseline within 1 h following exhaustive exercise, it is unlikely that factors responsible for the apoptotic response in lymphocytes maintain a prolonged presence once exercise has been terminated.