EFFECTS OF 4 WK INTENSIFIED TRAINING ON NATURAL KILLER (NK) CELLS IN COMPETITIVE SWIMMERS 902

Abstract

The purpose of this study was to examine the NK cell response to 4 wk intensified training in competitive swimmers. NK cell number and cytotoxic activity were assessed in 22 competitive swimmers (14-22 yr). Blood samples were obtained before, after and 1.5 hr after a standard 1.5 hr (5500 m) exercise session before (wk 0) and after (wk 4) 4 wk intensified training (40% volume increase). NK cell (CD3-/CD16+/CD56-) number was assessed by three color flow cytometry and NK cytotoxic activity (NKCA) measured in a whole blood 51Cr release assay. Compared with pre-exercise levels, NK cell number and NKCA decreased immediately and 1.5 hr after exercise at both wk 0 and wk 4 (P < 0.001). NKCA was lowest immediately after exercise returning near pre-exercise levels by 1.5 hr post-exercise; in contrast, NK cell number declined immediately post-exercise, and continued to decline 1.5 hr post-exercise. NK cell number did not change significantly from wk 0 to wk 4, although there was a trend for lower pre-exercise NK cell number at wk 4. For all time points pre- and post-exercise, NKCA was significantly lower at wk 4 compared with wk 0 (P < 0.005). NKCA per cell increased acutely (P < 0.001) immediately and 1.5 hr after exercise, with no significant change over the 4 wk. These data suggest that: (1) the acute NK cell response to swimming differs from the responses to running and cycling, (2) 1.5 hr intensive swimming stimulates NKCA per cell, and (3) 4 wk intensified swimming training may suppress some NK cell parameters.