Seventeen studies were identified (n=794). Sample size ranged from 13 to 190. Quality scores ranged from zero to 3.
Adaptive immunity: Nine studies showed no chronic or acute effects of exercise intervention on absolute circulating CD4+ (T helper) cells. Eight out of nine studies showed no chronic effects of training on CD8+ (effector T) cells. Two out of four studies reported showed acute exercise-induced increases in circulating CD8+ T cell numbers.
Innate immunity: Six studies showed no chronic effects of exercise intervention on natural killer (NK) cell numbers in peripheral blood. Four endurance training studies showed no chronic or acute effects of exercise on NK cell activity. One strength training study showed a chronic increase in women and another mixed intervention study showed a chronic decrease in men.
Inflammation: Two studies reported that regular endurance exercise reduced markers of inflammation. One study showed no change in C-reactive protein in the exercise group. Two studies reported that strength training had no effect on inflammatory markers.
One mixed and three endurance studies show no significant beneficial or detrimental effects of regular exercise on infection rates.