EFFECT OF HYDRATION STATE ON HEART RATE-BASED ESTIMATES OF VO2MAX.

Submaximal tests of aerobic fitness typically extrapolate oxygen consumption from heart rate. Because heart rate is influenced by hydration level, this study was conducted to investigate the effects of hydration status on the VO₂max scores predicted by a submaximal cycle ergometry assessment. Fifteen male cadets at the U.S. Air Force Academy took the heart rate-based USAF submaximal cycle ergometry fitness test twice over a 3-day period, once following a 12-hour fluid-restriction period (the dehydrated trial) and once following a hydration protocol in which the subjects drank a volume of water equivalent to 2% body weight 10 hours before the test and an additional volume equivalent to 1% body weight at least 30 minutes before the test (the hydrated trial). Prior to testing, subjects were weighed and a urine sample was collected. The urine specific gravity (USG) was measured using a refractometer. Our results indicated that, during the dehydrated trial, subjects' USG was significantly higher and their weight and VO₂max scores were significantly lower than during the hydrated trial. The change in the VO₂max score was significantly correlated to the change in percent body weight between the two trials. These data suggest that hydration status affects heart rate-based, submaximal estimates of VO₂max. [ABSTRACT FROM AUTHOR]