Journal Title (Medline/Pubmed accepted abbreviation): Appl. Physiol. Nutr. Metab.
Page Numbers: 698-706
Background: Dehydration can cause stress on the body leading to sub-optimal performance. Oxidative stress is a result of production of reactive oxygen species (ROS). Although some ROS are naturally formed during the act of exercising itself, excessive ROS production can lead to unhealthy amounts of inflammation and compromised cell function.
Hypothesis: Dehydration will increase oxidative stress, especially when dehydration occurs in hot environments.
Subjects: Seven male cyclists, competitive yet not used to training in the heat, age 36 ± 6 y
Experimental design: randomized, double-blind, cross-over design
Environment: warm environment (W): 33.9 ± 0.9°C or 93.0 ± 1.6°F or an environment with a neutral temperature (T): 23.0 ± 1.0°C or 73.4 ± 1.2°F.
Hydration: Dehydrated (DE): no fluid consumed during the trial or euhydrated (EU): fluid was consumed to match the mass lost during exercise (1 kg body weight lost = consumption of 1 L of water)
Protocol: The participants reported to the laboratory 5 times; the first time was to familiarize themselves with the experimental protocol and determine their lactate threshold (LT), and the other 4 times were to complete each of the 4 treatments. At least 1 wk separated the exercise trials. On the day of the trial, the participants arrived not having eaten for 2 hrs and having drunk 500 mL (about 2 cups) of water. They rested for 20 min while pre-test blood samples were collected, hydration status was confirmed, and body temperature and weight were measured. The subjects then cycled for 90 min at 95% of their previously determined LT. This exercise has been shown previously to cause ≥ 2% dehydration. Blood was collected at 45 min and 90 min. After a 15 min break, they completed a 5-km time trial. Afterwards, body weight and a final blood sample were collected. Blood was analyzed for oxidative stress with thiobarbituric acid reactive substances (TBARS) and total and oxidized glutathione serving as markers of oxidative stress.
Dehydration and heat stress are both stressful situations for the body, especially during exercise, and the combination was shown to greatly hinder performance. In this study, dehydration caused an increase in the oxidative state of the blood. Assure that athletes keep hydrated during sporting events. This can be done by weighing the athlete before training and at intervals during training. Some weight loss is okay, but losing more than 2% of body weight puts an athlete at risk for compromising performance. Sports beverages and/or water should be consumed during exercise, especially in warm environments.