Glycerol ineffective in boosting high-temperature exercise performance in athletes
The investigation, published in the Journal of the International Society of Sports Nutrition, found no significant impact of pre-exercise glycerol on dehydration, metabolic, kinematic or thermographic variables including blood lactate levels, relative oxygen uptake and heart rate in international race walkers. In the case of body mass loss after exercise, a measure of dehydration, glycerol was even outperformed by a water placebo.
“It is clear that we must continue to look for solutions for athletes competing in high temperature and humidity conditions, due to the increase in global temperature and the fact that the most important competitions are held in August, which is usually the hottest month of the year,” Francisco Javier Martínez-Noguera of the Catholic University of Murcia, Spain and colleagues wrote.
Lack of effect
The study recruited eight athletes with a minimum of 10 years of experience in race walking, three years of experience in international competitions, a maximum time of 2 hours 37 minutes in the Spanish 35 km Race Walking Championships and qualification for the Walking Race World Cup in Oman in 2022. The athletes had a mean age of 28 years, mean body mass of 65.6 kg, mean height of 180 cm and a maximum oxygen volume (VO2MAX) of 66.5 ml/kg/min.
The participants received medical examinations and then drank 1 g/kg of body mass of glycerol with 26 ml/kg of flavored water or the flavored water alone as a placebo in a crossover design. Two hours after the drink, the participants used a treadmill to perform a standardized rectangular test, consisting of high-intensity sets of exercise at 14.5 km/h alternating with periods of recovery exercise at 11.5 km/h and rests. The temperature and relative humidity of the laboratory during the test were 28.3°C and 31.5% respectively in the case of glycerol and 28.1°C and 31.4% in the case of the placebo.
The investigators found a significant interaction between time and treatment in body mass loss during the rectangular test, with the glycerol seeing more loss than the placebo (-2.48 kg vs -2.23 kg respectively). However, they found no significant interactions between time and treatment in other dehydration factors including urine-specific gravity and urine volume, though they noted “a moderate to large effect size.”
The researchers also found no significant effect of glycerol on the rate of perceived exertion or on a range of other exercise performance factors.
It is possible that the selected temperature and humidity were not sufficiently stressful to generate differences in the different variables evaluated, noted Martínez-Noguera et al.
'Equivocal' evidence
Commenting independently, Susan Kleiner, chief science officer at the U.S. company Electrolyte Boost, told NutraIngredients that it is a “well designed study under conditions that are common in warm climates.”
“Historically research results on glycerol are equivocal,” she said. “This data may lend weight to the argument that glycerol is ineffective against dehydration and performance enhancement under warm climate conditions.”
The results were not surprising, Kleiner said, adding that most elite athletes are at least somewhat acclimatized to moderate temperatures. “However, we still can’t say if the temperatures were more extreme whether glycerol may or may not help,” she said.
Without individual data points, a missing part of the puzzle is the response to glycerol between each athlete, with some potentially being responders and others being non-responders, Kleiner noted.
Also commenting independently, Chris Mohr, Fitness and Nutrition Advisor at Fortune Recommends Health, observed that “the commercialization of glycerol for exercise might be overhyped,” advising caution with claims of its benefits in enhancing performance.
In any case, athletes must regularly consume water and electrolytes to stay hydrated during exercise in high temperatures, Mohr added. Acclimatization, ice packs, cold towels and lightweight clothing can also help, he said.
Source: Journal of the International Society of Sports Nutrition 2024, 21(1)
doi: 10.1080/15502783.2024.2346563
“Effects of pre-exercise glycerol supplementation on dehydration, metabolic, kinematic, and thermographic variables in international race walkers”
Authors: Francisco Javier Martínez-Noguera et al.
