The purpose of this study was to examine the effect of prior glycerol loading on competitive Olympic distance triathlon performance (ODT) in high ambient temperatures. Ten (3 female and 7 male) well-trained triathletes (VO2max = 58.4 ±2.4 ml-kg−1 min−1; best ODT time = 131.5 ± 2.6 min) completed 2 ODTs (1.5-km swim, 40-km bicycle, 10-km run) in a randomly assigned (placebo/ glycerol) double-blind study conducted 2 weeks apart. The wet-bulb globe temperature (outdoors) was 30.5 + 0.5 °C (relative humidity: 46.3 ± 1.1%; hot) and 25.4 + 0.2 °C (relative humidity: 51.7 ± 2.4%; warm) for day 1 and day 2, respectively. The glycerol solution consisted of 1.2 g of glycerol per kilogram of body mass (BM) and 25 ml of a 0.75 g · kg−1 BM carbohydrate solution (Gatorade®) and was consumed over a 60-min period, 2 hours prior to each ODT. Measures of performance (ODT time), fluid retention, urine output, blood plasma volume changes, and sweat loss were obtained prior to and during the ODT in both the glycerol and placebo conditions. Following glycerol loading, the increase in ODT completion time between the hot and warm conditions was significantly less than the placebo group (placebo 11:40 min vs. glycerol 1:47 min; p < .05). The majority of the performance improvement occurred during the final 10-km run leg of ODT on the hot day. Hyperhydration occurred as a consequence of a reduced diuresis (p < .05) and a subsequent increase in fluid retention (p < .05). No significant differences were observed in sweat loss between the glycerol and placebo conditions. Plasma volume expansion during the loading period was significantly greater (p < .05) on the hot day when glycerol appeared to attenuate the performance decrement in the heat. The present results suggest that glycerol hyperhydration prior to ODT in high ambient temperatures may provide some protection against the negative performance effects of competing in the heat.
Aaron Coutts, Peter Reaburn, Kerry Mummery and Mark Holmes
Kimberly Volterman, Daniel Moore, Joyce Obeid, Elizabeth A. Offord and Brian W. Timmons
In adults, rehydration after exercise in the heat can be enhanced with a protein-containing beverage; however, whether this applies to children remains unknown. This study examined the effect of milk protein intake on postexercise rehydration in children.
Fifteen children (10–12 years) performed three exercise trials in the heat (34.4 ± 0.2 °C, 47.9 ± 1.1% relative humidity). In a randomized, counterbalanced crossover design, participants consumed iso-caloric and electrolyte-matched beverages containing 0 g (CONT), 0.76 g (Lo-PRO) or 1.5 g (Hi-PRO) of milk protein/100 mL in a volume equal to 150% of their body mass (BM) loss during exercise. BM was then assessed over 4 h of recovery.
Fluid balance demonstrated a significant condition × time interaction (p = .012) throughout recovery; Hi-PRO was less negative than CONT at 2 hr (p = .01) and tended to be less negative at 3 h (p = .07). Compared with CONT, beverage retention was enhanced by Hi-PRO at 2 h (p < .05).
A postexercise beverage containing milk protein can favorably affect fluid retention in children. Further research is needed to determine the optimal volume and composition of a rehydration beverage for complete restoration of fluid balance.
M.J. Anderson, J.D. Cotter, A.P. Garnham, D.J. Casley and M.A. Febbraio
This study examined the effect of glycerol ingestion on fluid homeostasis, thermoregulation, and metabolism during rest and exercise. Six endurance-trained men ingested either 1 g glycerol in 20 ml H2O · kg−1 body weight (bw) (GLY) or 20 ml H2O · kg−1 bw (CON) in a randomized double-blind fashion, 120 min prior to undertaking 90 min of steady state cycle exercise (SS) at 98% of lactate threshold in dry heat (35 °C, 30% RH), with ingestion of CHO-electrolyte beverage (6% CHO) at 15-min intervals. A 15-min cycle, where performance was quantified in kJ, followed (PC). Pre-exercise urine volume was lower in GLY than CON (1119 ± 97 vs. 1503 ± 146 ml · 120 min−1; p < .05). Heart rate was lower (p < .05) throughout SS in GLY, while forearm blood flow was higher (17.1 ± 1.5 vs. 13.7 ± 3.0 ml · 100 g tissue · min−1; < .05) and rectal temperature lower (38.7 ± 0.1 vs. 39.1 ± 0.1 °C; p < .05) in GLY late in SS. Despite these changes, skin and muscle temperatures and circulating catecholamines were not different between trials. Accordingly, no differences were observed in muscle glycogenolysis, lactate accumulation, adenine nucleotide, and phosphocreatine degradation or inosine 5′-monophosphate accumulation when comparing GLY with CON. Of note, the work performed during PC was 5% greater in GLY (252 ± 10 vs. 240 ± 9 kJ;p < .05). These results demonstrate that glycerol, when ingested with a bolus of water 2 hours prior to exercise, results in fluid retention, which is capable of reducing cardiovascular strain and enhancing thermoregulation. Furthermore, this practice increases exercise performance in the heat by mechanisms other than alterations in muscle metabolism.
Paola Rodriguez-Giustiniani and Stuart D.R. Galloway
as drink composition and volume ( Shirreffs & Maughan, 2000 ), but it is also believed that hormonal changes associated with the menstrual cycle can influence fluid retention ( Fortney, 1996 ). Although fluid replacement after dehydration has been extensively studied in males, there have been few
Eric Kyle O’Neal, Samantha Louise Johnson, Brett Alan Davis, Veronika Pribyslavska and Mary Caitlin Stevenson-Wilcoxson
large shifts in fluids are not incurred, and hormonal regulation of fluid retention responses by arginine vasopressin are more uniformly produced when considerable fluid deficit is experienced ( Cheuvront & Kenefick, 2014 ; Cheuvront et al., 2013 ). It is plausible that the physiological and hormonal
Alan J. McCubbin, Bethanie A. Allanson, Joanne N. Caldwell Odgers, Michelle M. Cort, Ricardo J.S. Costa, Gregory R. Cox, Siobhan T. Crawshay, Ben Desbrow, Eliza G. Freney, Stephanie K. Gaskell, David Hughes, Chris Irwin, Ollie Jay, Benita J. Lalor, Megan L.R. Ross, Gregory Shaw, Julien D. Périard and Louise M. Burke
than Na + loading over an extended period ( McCubbin et al., 2019a ). Glycerol, a three-carbon alcohol, is another effective osmolyte that enhances fluid retention and results in expansion of P v and a reduction in urine output. Glycerol was removed from the World Anti-Doping Agency Prohibited List
rehydration intervention for P Osmol (p=0.008), Δ P V (p<0.001), and rating of thirst (p<0.001), but not total body water (p=0.830). No trial differences were observed. Total fluid intake did not differ between trials (CM: 24.2ml/kg vs CEB: 24.0ml/kg; p=0.907). However, there was greater fluid retention (CM
in healthy subjects. Moreover, it is unclear whether increases in lean body mass are due to increases in “true” muscle tissue or due to fluid retention and increased extracellular water volume. In addition, it remains uncertain if the GH lipolytic effect influences exercise performance. Finally, the
Trent Stellingwerff, Ingvill Måkestad Bovim and Jamie Whitfield
concern that is of particular relevance for weight-dependent runners is the potential for increased fluid retention, and therefore an increase in BM, as a result of the increased sodium intake ( Sims et al., 2007a , 2007b ). Taken together, these findings suggest that supplementation with NaHCO 3 − has
Gary J. Slater, Jennifer Sygo and Majke Jorgensen
benefit for both maximal and repeat sprint efforts and weight room activities Possibly; sprinters must weigh potential performance benefits vs. energetic costs associated with extra body mass and fluid retention that may occur with creatine monohydrate supplementation Bemben and Lamont ( 2005 ), Haff et