Oxidative stress in half and full Ironman triathletes.

INTRODUCTION: Ultraendurance athletes who maintain a very high volume of exercise may, as a result of greater production of reactive oxygen species (ROS), be particularly susceptible to oxidative damage.
PURPOSE: This study sought to examine and compare pre- and postrace markers of oxidative stress in ultraendurance athletes training for, and competing in, either a half or a full Ironman triathlon.
METHODS: Resting and postexercise blood was sampled from 16 half Ironman triathletes, 29 full Ironman triathletes, and age-matched, relatively inactive controls. Blood was analyzed for markers of oxidative stress (malondialdehyde (MDA) concentration) and antioxidant status (glutathione peroxidase (GPX), catalase (CAT), and superoxide dismutase (SOD) activities).
RESULTS: Compared with controls, the half Ironman triathletes had significantly (P < 0.001) higher erythrocyte GPX activity at rest, whereas the Ironman triathletes had significantly (P < 0.05) lower resting plasma MDA and significantly (P < 0.05) greater resting activities of GPX and CAT compared with controls. As a result of the half Ironman triathlon, there was a significant (P < 0.05) increase in MDA and significant (P < 0.05) decreases in erythrocyte GPX, SOD, and CAT activities. These changes also occurred in response to the Ironman triathlon; MDA significantly (P < 0.05) increased, and there were significant (P < 0.001) decreases in GPX, CAT, and SOD activities. Users of antioxidant supplements in both the half and full Ironman races had significantly (P < 0.05) elevated MDA after races compared with nonsupplementers.
CONCLUSION: The present investigation indicates that training for and competing in half and full Ironman triathlons has different effects on erythrocyte antioxidant enzyme activities and oxidative stress.