Leukocyte counts and lymphocyte responsiveness associated with repeated bouts of strenuous endurance exercise

This study compared leukocyte counts and lymphocyte responsiveness during a nd after a second bout of high-intensity endurance exercise on the same day with the response to a similar but single bout of exercise. Nine athletes participated in three 24-h trials: 1) rest in bed (Rest); 2) one bout of ex ercise (One); and 3) two bouts of exercise (Two). All bouts consisted of 75 min at similar to 75% of maximal O-2 uptake on a cycle ergometer. Lymphocy tes in whole blood were stimulated with monoclonal antibodies against CD2 a nd assessed by flow cytometry for expression of the early activation molecu le CD69. The second bout of exercise in the Two trial was associated with s ignificantly increased concentrations of total leukocytes, neutrophils, lym phocytes, CD4(+), CD8(+), and CD56(+) cells and a significantly decreased p ercentage of CD56(+) cells expressing CD69 compared with a single bout. Add itionally, there was a significantly decreased CD69 fluorescence in CD56(+) cells postexercise. These differences suggest a "carry-over" effect in the immune system from a first to a second bout of exercise on the same day.