title: 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.
authors.affiliation: Department of Physiology and Pharmacology, James Cook University, Townsville, QLD, Australia. sam.hitchins@jcu.edu.au
authors.forename: S
authors.initials: S
authors.lastname: Hitchins
authors.forename: D T
authors.initials: DT
authors.lastname: Martin
authors.forename: L
authors.initials: L
authors.lastname: Burke
authors.forename: K
authors.initials: K
authors.lastname: Yates
authors.forename: K
authors.initials: K
authors.lastname: Fallon
authors.forename: A
authors.initials: A
authors.lastname: Hahn
authors.forename: G P
authors.initials: GP
authors.lastname: Dobson
mesh_terms: D000328:Adult; D001628:Beverages; D001642:Bicycling; D001769:Blood; D001834:Body Water / Q000378:metabolism; D005990:Glycerol / Q000008:administration & dosage*; D006358:Hot Temperature; D006801:Humans; D006813:Humidity; D008297:Male; D009994:Osmolar Concentration; D010101:Oxygen Consumption; D010953:Plasma Volume; D012996:Solutions; D013997:Time Factors; D014556:Urine; D014867:Water / Q000008:administration & dosage*
chemical_list: D012996:Solutions; D014867:Water; D005990:Glycerol