Key Takeaway
Pre-exercise hyperhydration (including sodium loading) provides small-to-moderate improvement in endurance performance, with a Hedges' g of 0.31 for time-to-exhaustion tasks.
Summary
This meta-analysis examined the effects of pre-exercise oral hyperhydration strategies on endurance exercise performance, heart rate, and thermoregulation. Hyperhydration involves consuming fluids (often with osmotic agents like sodium or glycerol) before exercise to expand plasma volume and create a fluid reserve.
The review pooled data from multiple randomized controlled trials comparing hyperhydration protocols to euhydration controls. Pre-exercise hyperhydration strategies included sodium loading, glycerol-enhanced fluid intake, and large-volume water consumption before endurance exercise in the heat.
Results showed a small-to-moderate beneficial effect on time-to-exhaustion performance (Hedges' g = 0.31), supporting the use of pre-exercise hyperhydration as an ergogenic strategy, particularly in prolonged endurance events performed in hot conditions where sweat losses are high.
Methods
Systematic literature search of randomized controlled trials examining pre-exercise oral hyperhydration versus euhydration or placebo on endurance performance outcomes. Effect sizes calculated using Hedges' g with random-effects meta-analytic models. Subgroup analyses examined different hyperhydration agents and exercise modalities.
Key Results
- Pre-exercise hyperhydration produced a small-to-moderate improvement in time-to-exhaustion (Hedges' g = 0.31)
- Sodium-based hyperhydration protocols were among effective strategies for expanding plasma volume
- Hyperhydration attenuated rises in core temperature and heart rate during prolonged exercise
- Effects were most pronounced in hot environmental conditions
Limitations
- Heterogeneity in hyperhydration protocols (sodium, glycerol, water volume) across studies
- Most included studies used laboratory-based exercise protocols rather than real-world competition
- Limited data on time-trial performance (most studies used time-to-exhaustion)
- Publication bias cannot be excluded
- Practical applicability may vary with individual sweat rates and environmental conditions