Acute physical exercise has a large and positive effect on the level of NK-cell cytolytic activity in the peripheral blood (g = 1.02, 95% CI 0.59–1.46, p < 0.01).

In the first hours after performing sports, NKCA values return to baseline, but do not drop below the pre-exercise values (g = 0.06, 95% CI − 0.37 to 0.50, p < 0.76).

The data suggest the counterintuitive conclusion that the level of NKCA is not significantly altered by the changing numbers of NK-cells (k = 11, beta = 0.123, R2 = 0%, p = 0.55).