IMMUNE FUNCTION IN MARATHON VERSUS SEDENTARY CONTROLS

Marathon runners (N = 22) who had completed at least seven marathons ( (X) over bar +/- SEM = 23.6 +/- 5.7) and had been training for maratho n race events for at least 4 yr (12.3 +/- 1.3) were compared with sede ntary controls (N = 18). Although the two groups were of similar age ( 38.7 +/- 1.5 and 43.9 +/- 2.2 yr, respectively) and height, the marath on runners were significantly leaner and possessed a VO2max 60% higher than that of the controls. Neutrophil counts tended to be lower in th e group of marathoners, while other Leukocyte and lymphocyte subsets w ere similar to controls. Mitogen-induced lymphocyte proliferation did not differ between groups. Natural killer cell cytotoxic activity (NKC A) was significantly higher in the marathoners versus controls (373 +/ - 38 vs 237 +/- 41 total lytic units, respectively, a 57% difference, P = 0.02). For all subjects combined (N = 40) and within the group of marathon runners (N = 22), percent body fat was negatively correlated with NKCA (r = -0.48, P = 0.002; r = -0.49, P = 0.019, respectively), and age was negatively correlated with Con A-induced lymphocyte prolif eration (r = -0.41, P = 0.009; r = -0.53, P = 0.011, respectively). Th ese data indicate that NKCA but not mitogen-induced lymphocyte prolife ration is higher in marathon runners relative to sedentary controls.