Objective: To investigate homeostasis of the immune system in athletes with spinal cord injuries during and after racing a wheelchair marathon.
Design: The study examined changes in the number and function of natural killer (NK) cells in nine male wheelchair marathon athletes (spinal cord injuries between T5 and T12) who completed the 15th Oita International Wheelchair Marathon Race. Blood samples were obtained the day before, immediately after, and 1 day after the race. Blood samples were also obtained from seven age-matched control subjects with spinal cord injuries but who did not exercise regularly.
Results: The number of peripheral leukocytes increased (p < .01) immediately after the race. In contrast, the number of peripheral NK cells and NK cell cytotoxic activity significantly decreased from 310+/-130/microL to 133 +/-61/microL and from 42.6%+/-3.0% to 38.2%+/-3.2%, respectively (mean+/-SD), immediately after the race. Plasma cortisol levels were increased after the race. However, all parameters returned to control levels within 24 hours. Measurements in control subjects did not change throughout the experiment.
Conclusion: These findings suggest that racing a marathon suppressed peripheral NK cell number as well as NK cell cytotoxic activity in wheelchair athletes and that this was probably mediated by increased postrace cortisol levels. Wheelchair marathon athletes are advised to take extra precaution to avoid infection within 24 hours after racing because of the transient suppression of NK cell cytotoxic activity during this period.