Effects of strength exercise and training on the natural killer cell counts in elderly humans

Background. To investigate the effects of strength exercise and training on the natural killer cell counts in elderly humans. Methods. The study examined strength exercise-induced changes in the number of NK cells and changes in stress hormones in 16 sedentary elderly subjects before and after a 8-week strength training intervention. Blood samples were obtained before, immediately and 6 hours after a standardized strength test. Blood samples were also obtained from ten sedentary young subjects, under the same conditions and from ten resting elderly subjects serving as time controls. Results. Prior to training, older adults immediately decreased (from 165.4 +/- 19.5 muL to 110.6 +/- 14.3 muL; mean +/- SEM) their NK cell count in response to the standardized strength test, whereas young controls increased their count (from 157.6 +/- 28.8 muL(-1) to 241.4 +/- 39.8 muL(-1)). After strength training, the same old subjects slightly increased (from 159 +/- 19.8 muL(-1) to 166.6 +/- 19.7 muL(-1)) their NK cell counts in response to the standardized strength test. In elderly subjects, no increase in stress hormone was observed following the strength test either before or after the strength training programme. Conclusions. The results suggest that in sedentary older adults, unlike young subjects, strength exercises can induce a transient decrease in NK cell count which can be cancelled by a short-term strength conditioning. Therefore, caution should be taken regarding immunocompetence of older adults when initiating a rehabilitation programme based on strength.