The critical level of water deficit causing a decrease in human exercise performance: a practical field study.

Area of Science:

• Exercise Physiology
• Sports Science
• Human Performance

Background:

• Dehydration is a common concern for athletes, potentially impacting physiological responses and performance.
• Understanding the critical thresholds of dehydration for both aerobic and anaerobic exercise is crucial for optimizing athletic training and competition.

Purpose of the Study:

• To determine the critical level of water deficit that leads to decreased aerobic and anaerobic exercise performance.
• To compare the effects of varying fluid ingestion levels on exercise performance during prolonged activity in the heat.

Main Methods:

• Two experiments involving regular baseball players measured step test score (aerobic) and maximal anaerobic power (anaerobic) during cycling.
• Participants underwent four fluid ingestion conditions (80%, 60%, 40%, 20% of sweat loss) on hot days, with body mass loss (Delta m(b)) tracked.

Main Results:

• Significant body mass loss occurred with decreased fluid ingestion.
• Aerobic performance (step test score) decreased significantly at Delta m(b) > 2.4% (40% fluid ingestion).
• Anaerobic performance (maximal anaerobic power) remained stable up to 2.5% Delta m(b) but decreased significantly at 3.9% Delta m(b) (20% fluid ingestion).

Conclusions:

• A critical level of dehydration exists that impairs both aerobic and anaerobic exercise performance.
• Aerobic performance appears more susceptible to dehydration than anaerobic power output during exercise-induced dehydration.