Effect of exercise-induced dehydration on time-trial exercise performance: a meta-analysis

Area of Science:

• Exercise Physiology
• Sports Science
• Performance Nutrition

Background:

• Exercise-induced dehydration (EID) is a common physiological state during prolonged physical activity.
• The impact of EID on exercise performance, particularly time-trial (TT) performance, remains a subject of investigation.
• Understanding fluid balance and its effects is crucial for optimizing athletic outcomes.

Purpose of the Study:

• To quantitatively assess the effect of exercise-induced dehydration on time-trial exercise performance using meta-analytical methods.
• To determine the magnitude of EID's impact on cycling TT performance.
• To compare the influence of EID with other exercise parameters like intensity and duration.

Main Methods:

• Systematic literature searches and cross-referencing were employed to identify relevant studies.
• Data from five studies involving cycling TTs were meta-analyzed, converting performance outcomes to mean percentage changes in power output.
• Random-effects model meta-regressions were utilized to analyze the relationship between body weight loss due to EID and TT performance.

Main Results:

• EID, with an average body weight loss of 2.20%, did not significantly alter cycling TT performance (0.06 ± 2.72% change in power output, p=0.94).
• Meta-regression revealed that exercise intensity and duration significantly influenced power output changes, whereas EID-associated body weight loss did not.
• Drinking according to thirst sensation led to improved TT performance compared to drinking below or above thirst levels.

Conclusions:

• Exercise-induced dehydration, even up to 4% body weight loss, does not negatively affect cycling performance under outdoor conditions.
• Exercise intensity and duration are more critical determinants of cycling TT performance than EID.
• Adhering to thirst sensation for fluid intake is the optimal strategy for maximizing cycling TT performance.