Conflicting results exist on whether glycerol hyperhydration reduces cardiovascular and thermal strain while improving endurance performance. Few studies have used a protocol that mimics athletic performance; none have been done on running performance.
PURPOSE: To test glycerol hyperhydration (Gly) against water hyperhydration (Pl) on the ability to reduce cardiovascular and thermal strain and improve performance when subjects run a set distance as quickly as possible. We tested the hypotheses that compared with water hyperhydration, glycerol hyperhydration would result in: a.) greater fluid retention; b.) no differences in heart rates and core temperatures, and; c.) decreased run time performances.
METHODS: Six endurance trained runners (males, age: 27.8±6.0 years, percent body fat: 7.5±4.0%, VO2peak: 60.7±6.2 ml·kg-1·min-1) completed a treadmill run in an environmental chamber at a self-selected pace, estimated to take 1 hour. Temperature was set at 30°C and 50% relative humidity. A randomized, double-blind, cross-over design was used. Beginning 2.5 hours prior to exercise, Gly was given as 1.2 g·kg-1 bodyweight with a total fluid ingestion of 26 ml·kg-1 bodyweight, or Pl was given as water of an equal amount. Runners ingested up to 500 ml during the run and were unable to see their elapsed time or chosen speed, only distance covered.
RESULTS: Fluid retention was not different between Gly and Pl (Gly = 977 ±328 ml, Pl = 391±546 ml, p > 0.05). Time to complete the run was not different between trials (Gly = 4074 ±229 s, Pl = 4079 ±295 s, p > 0.05). Heart rate, core temperature and RPE were not different between trials (p>0.05) at any distance during the run.
CONCLUSIONS: For a run lasting 68 minutes in hot conditions, glycerol hyperhydration was not beneficial over water hyperhydration for altering cardiovascular strain, thermal strain, or running performance.