A high-dose sodium drink can increase blood plasma volume and endurance performance without affecting the body's heat regulation systems, according to an American study.
Maintaining blood volume is a key factor in optimally performing endurance exercises. It is crucial for ensuring an adequate supply of oxygen and nutrients to the working muscles and facilitates the removal of metabolic waste. The need to maintain plasma volume is also crucial, as significant amounts of heat are produced by metabolism leading to competition of blood flow between the skin and muscles.
One way to increase plasma volume is to add sodium to the diet, which, however, may, undesirably, prevent perspiration, resulting in impaired thermal regulation during exercise.
The aim of this study was to find out if a dose of sodium (eg, by supplementation) with a low volume of fluid (IPOSL) taken orally just prior to exercise can increase the plasma volume of young healthy men and improve their performance during a 15-minute time trial without to affect the thermal regulation measured by welding rate and core temperature.
14 moderately fit recreational cyclists aged 23-32 participated in 2 identical trials. These consisted of cycling for 45 minutes below the maximum power limit, followed by a 15 minute time trial against a constant resistance at maximum power following administration of one of the following drinks:
- a high dose sodium (IPOSL) solution with a total volume of 10 ml per body weight, divided into 3 equal portions, which were drunk at 15-minute intervals
- a drink with the same total volume, drunk in the same way, but as a placebo without sodium
The opposing drink compositions led to significant differences in the resting plasma before exercise. The IPOSL drink led to a 3.1% expansion, while the placebo drink even led to a 4.7% reduction in volume.
After the beginning of the exercise, the plasma volume of the participants of both experimental groups decreased by a significant percentage, which did not change during the exercise phase. With the IPOSL Drink, plasma volume was maintained at 15 and 30 minutes after the start of the exercise to a greater extent than with the placebo drink. After 45 minutes, however, this effect was lost.
Nonetheless, IPOSL group participants performed significantly more during the subsequent 15-minute time trial. They drove just under 1 km further than the drivers who had taken the placebo drink. With regard to heart rate, core temperature as well as the rate of perceived fatigue or total body sweat rate, no differences were found between the groups. This suggests that the high-dose sodium drink had no negative effects on heat regulation.
The strangest of these results was the fact that cyclists performed better in the time trial after taking the IPOSL drink, even though the plasma volume impact had already been exhausted.
The scientists point out that these differences in performance may have been caused by the reduction in basal plasma volume in the placebo trial rather than by the increase in the IPOSL group. They believe that further research is needed to uncover the true reason for their results.
Also read: Does Vitamin E increase endurance?