Fluid Replacement In The Heat

Abstract

Provision of fluid to offset dehydration is a priority during exercise in the heat, but the benefit of substances other than carbohydrate or electrolytes added to the fluid has not been demonstrated. PURPOSE To compare physiological responses, fluid availability and retention of sports drinks with and without betaine (an organic osmolyte derived from glycine) during prolonged cycling in warm, humid conditions. METHODS Eight trained male cyclists volunteered to participate in a double-blind, cross-over study. Subjects cycled for 120 min alternating between 60% and 75%VO2max followed by a 15 min time trial (TT) under 3 treatments: placebo (P), 6%CHO drink (CHO), or 7%CHO + Betaine (BET). Accumulation of heavy water (D2O) in plasma was the marker for relative fluid delivery. RESULTS Rectal temperature was similar among P, CHO, and BET trials. Blood glucose was not increased with CHO or BET compared to P during cycling. Perceived exertion, heart rate, blood lactate, plasma volume changes, plasma [D2O], and fluid retention were similar across trials. Total work performed during TT was not different among trials, although it tended to be lower with P by 14% and 10% compared to CHO and BET, respectively. Following cycling, there was a significantly greater loss (p < 0.05) of knee extensor isometric strength with P (18.8 ± 2.0%) and CHO (16.3 ± 2.0%) compared to BET (12.8 ± 1.7%). CONCLUSIONS No performance advantage was gained with CHO and fluid availability was similar to P during prolonged variable intensity cycling. Although BET did not improve performance or hydration status during cycling, maintenance of strength was improved following exercise in the heat. Supported by a grant from The Coca-Cola Company