Sodium-facilitated hypervolemia, endurance performance, and thermoregulation

Area of Science:

• Exercise Physiology
• Sports Nutrition
• Human Performance

Background:

• Maintaining plasma volume is crucial for endurance exercise performance.
• Pre-exercise hydration strategies aim to optimize fluid balance and performance.
• The impact of acute sodium loading on exercise physiology requires further investigation.

Purpose of the Study:

• To examine the effects of an immediate pre-exercise, orally ingested, sodium load (IPOSL) on plasma volume, endurance performance, and thermoregulation.
• To compare the effects of a sodium-containing beverage versus a placebo on key physiological variables during exercise.

Main Methods:

• Fourteen male participants ingested either an isotonic sodium load (164 mEq Na+) or a hypotonic placebo beverage.
• Participants performed a 45-minute cycling exercise at 70% maximal work rate, followed by a 15-minute performance time trial.
• Plasma volume, cardiovascular, and thermoregulatory responses were monitored throughout the protocol.

Main Results:

• IPOSL led to a 3.1% expansion in resting plasma volume, while the placebo caused a 4.7% reduction.
• Plasma volume was better maintained during exercise with IPOSL compared to placebo at 15 and 30 minutes.
• Time trial performance improved by approximately 7.8% following IPOSL ingestion (p < 0.05).
• No significant differences in heart rate, core temperature, perceived exertion, or sweat rate were observed between conditions.

Conclusions:

• Immediate pre-exercise sodium loading effectively increases plasma volume and enhances endurance performance.
• This strategy appears to maintain plasma volume during the initial stages of exercise.
• Pre-exercise sodium intake improves time trial performance without compromising thermoregulation.