Effectiveness of commercial versus homemade sports drinks on fluid balance and exercise capacity during high-intensity intermittent exercise

Commercial sports drinks are used widely by athletes involved in high-intensity intermittent (HII) exercise. However, little has been reported on their relative effectiveness compared to simple homemade drink formulations. The purpose of this study was to investigate the effects of different sports drink formulations (commercial v homemade), water and no drink on fluid balance and exercise capacity during HII exercise. Twelve trained men (age: 27 ± 2.1 y) performed a 90-min HII running protocol designed to simulate activity experienced during a football match. The protocol was arranged in six 15-min stages where running speeds ranged between 55% and 120% of VO2max. The HII protocol included half-time and a run to fatigue post 90 min. Using a single-blind, randomized, cross-over design, participants ingested a preload of 5 mlkg-1 10 min before HII exercise and 3 mlkg-1 every 15 min of either Isostar® (ISO), a homemade sports drink (CHO), placebo (P) or no drink (ND). Blood lactate (Hla), blood glucose (Bgluc), heart rate (HR) and ratings of perceived exertion (RPE) were measured before, during (every 15 min) and after the 90-min HII protocol. Changes in plasma volume were measured at half-time and post 90 min. Sweat rate and fluid balance were calculated post each trial. Time to fatigue (TTF) was recorded at exhaustion. In the ND trial, TTF decreased by approximately 17%, 28% and 43% compared to P, CHO and ISO, respectively (p<0.01) and HR was highest at 90 min following ND trial (p<0.05). TTF was 20% longer in the ISO trial compared to CHO, but this difference was not statistically significant (p>0.05). No differences were noted in HLa, RPE, PV or SR between the trials (p>0.05) but there were significant effects of time (p<0.05). Bgluc peaked at 30 minutes in ISO and CHO, but dropped by ~27% in ISO and by ~30% in CHO after half time. Absence of fluid ingestion surprisingly had no significant effect on altering plasma volume or decreasing sweat rate despite causing noticeable decreases in exercise capacity. The homemade drink improved exercise capacity in a similar manner to that of the commercial drink, but neither sports drink achieved superior hydration compared to water. Ingestion of exogenous carbohydrate through sports drink consumption caused an exercise-induced glycemic response when exercise was restarted after half-time. This decline in blood glucose after half-time appears to be marginally attenuated in P trial. A possible suggestion for team sports could be to drink water rather than sports drink prior to half-time period.