Pre-Exercise Glycerol Hydration Improves Cycling Endurance Time

Abstract

The effects of glycerol ingestion (GEH) on hydration and subsequent cycle ergometer submaximal load exercise were examined in well conditioned subjects. We hypothesized that GEH would reduce physiologic strain and increase endurance. The purpose of Study I (n = 11) was to determine if pre-exercise GEH (1.2 gm/kg glycerol in 26 ml/kg solution) compared to pre-exercise placebo hydration (PH) (26 ml/kg of aspartame flavored water) lowered heart rate (HR), lowered rectal temperature (Tc), and prolonged endurance time (ET) during submaximal load cycle ergometry. The purpose of Study II (n = 7) was to determine if the same pre-exercise regimen followed by carbohydrate oral replacement solution (ORS) during exercise also lowered HR, Tc, and prolonged ET. Both studies were double-blind, randomized, crossover trials, performed at an ambient temperature of 23.5-24.5 degrees C, and humidity of 25-27%. Mean HR was lower by 2.8 +/- 0.4 beats/min (p = 0.05) after GEH in Study I and by 4.4 +/- 1.1 beats/min (p = 0.01) in Study II. Endurance time was prolonged after GEH in Study I (93.8 +/- 14 min vs. 77.4 +/- 9 min, p = 0.049) and in Study II (123.4 +/- 17 min vs. 99.0 +/- 11 min, p = 0.03). Rectal temperature did not differ between hydration regimens in both Study I and Study II. Thus, pre-exercise glycerol-enhanced hyperhydration lowers HR and prolongs ET even when combined with ORS during exercise. The regimens tested in this study could potentially be adapted for endurance activities.

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

“…It is presumed that the cause of relatively low performance improvements is because of large individual differences and the fact that the subjects were inexperienced in cycling as they were middle-distance athletes. Several previous studies report an improvement in exercise performance due to glycerol loading (Montner et al, 1996 ;Hitchins et al, 1999 ;Anderson et al, 2001). Although this study did not show any improvement effect due to glycerol loading, it might be observed depending on the exercise conditions (temperature, humidity, exercise genre and movement time).…”

“…1) HW is taken in 60 min (HW); 2) HW containing 1.2g of glycerol (a designated food additive supplied by Kishida Chemical Co., Ltd.,) per kilogram of body weight is taken in 60 min (G), 3) High concentration glycerol (1.0g per kilogram) is taken at fi rst and then HW is taken in 90 min (Bolus-G). 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.…”

“…Thus, the water retention effects of two different glycerol loading methods were investigated in the same subject in Experiment 1. The methods used in the experiment were: the Bolus-G protocol as used by Montner et al (1996) and which is regarded as most effective in water retention; the G protocol whose effect is estimated to be second to Bolus-G; and, the HW protocol was used as a control which did not contain glycerol. Signifi cant water retention effects of glycerol loading were observed in this study.…”

“…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.…”