The effect of strenuous physical exercise on circulating blood lymphocytes and serum cortisol levels.

Venous blood was removed from healthy subjects immediately before and at intervals after exercise on a bicycle ergometer. Immediately after exercise, the subjects developed a lymphocytosis in which (a) the E-rosette percentage fell by 10% but their absolute number in the circulating blood rose by more than 70%, (b) the percentage of PHA-stimulated cells fell, but their absolute numbers increased considerably and (c) the absolute numbers of Con A- and PWM-responding cells increased. The numbers of lymphocytes in the various subpopulations had returned virtually to the pre-exercise levels 15 minutes after stopping exercise. During the response to exercise, the characteristics of the cells in the various subpopulations did not show any major changes, despite considerable and rapid fluctuations in numbers: it is suggested that exercise discharges intravascularly sequestered cells and that cortisol may be involved in re-sequestration of stress-released cells. It is recommended that, in clinical studies on circulating lymphocyte numbers and populations, the patient should be rested for at least 15 minutes before venesection.