Glycerol hyperhydration improves cycle time trial performance in hot humid conditions

Abstract

Eight competitive cyclists [mean peak oxygen consumption, (VO2(peak)) = 65 ml x min(-1) x kg(-1)] undertook two 60-min cycle ergometer time trials at 32 degrees C and 60% relative humidity. The time trials were split into two 30-min phases: a fixed-workload phase and a variable-workload phase. Each trial was preceded by ingestion of either a glycerol solution [1 g x kg(-1) body mass (BM) in a diluted carbohydrate (CHO)-electrolyte drink] or a placebo of equal volume (the diluted CHO-electrolyte drink). The total fluid intake in each trial was 22 ml x kg(-1) BM. A repeated-measures, double blind, cross over design with respect to glycerol was employed. Glycerol ingestion expanded body water by approximately 600 ml over the placebo treatment. Glycerol treatment significantly increased performance by 5% compared with the placebo group, as assessed by total work in the variable-workload phase (P < 0.04). There were no significant differences in rectal temperature, sweat rate or cardiac frequency between trials. Data indicate that the glycerol-induced performance increase did not result from plasma volume expansion and subsequently lower core temperature or lower cardiac frequencies at a given power output as previously proposed. However, during the glycerol trial, subjects maintained a higher power output without increased perception of effort or thermal strain.

Alleviation of Exercise-induced Dehydration under Hot Conditions by Glycerol Hyperhydration

“…The Bolus-G protocol established by Montner, et al, (1996) is considered tobe the most effective water intake method for internal water retention (Robergs and Griffi n, 1998). In contrast, G protocol, where a specifi c concentration of glycerol solution is taken, has been used in many other studies (Hitchins, et al, 1999;Anderson, et al, 2001;Marino, et al, 2003. The total water amount taken in each protocol was determined to be 25ml per kilogram of body weight, and the total glycerol amount taken in G and Bolus-G protocols to be 1.2g per kilogram of body weight.…”

“…The cycling exercise consists of a three-minutes warm-up (50% of specifi ed load intensity), a 40 min phase pedaling with a rotation frequency of 60 rpm (fi xed power phase) and a 30-min phase pedaling at maximum power (variable power phase) (Jeukendrup, et al, 1996;Hitchins, et al, 1999). The exercise performance of each subject was evaluated from the total work load (kJ) at the variable power phase.…”

“…The defi nition of hyperhydration is for the body to be in a state with more water content than usual. It is reported that pre-exercise hyperhydration can enhance thermoregulatory functions during exercise under hot conditions (Lyons, et al, 1990) and improve exercise performance (Montner, et al, 1996;Hitchins, et al, 1999;Anderson, et al, 2001). Preventing dehydration during exercise is important in Japan which is known for hot and humid conditions.…”

“…Although several studies have so far reported improvements in performance during exercise under hot conditions through pre-exercise glycerol loading (Montner, et al, 1996;Hitchins, et al, 1999;Anderson, et al, 2001), there also have been reports of its ineffectiveness (Marino, et al, 2003). Differences in hydration methods and the amount of pre-exercise water retention in each study may have caused these different results.…”

Human Water and Electrolyte Balance

“…[68][69][70] The effects of glycerol hyperhydration on performance are mixed. Glycerol hyperhydration may [71][72][73] or may not 69,70 improve exercise performance. Comparing study outcomes is complicated by differences in performance measures, climate, and the potentially confounding study design limitations.…”