Controlled Cold Water and Water Slushy Ingestion and Heat Performance in Subjects of Average Fitness

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PURPOSE: To examine the effects of controlled (volume/body mass) ingestion of cold water and water slushy on performance in a dry, hot environment in subjects of average cardiorespiratory fitness. METHODS: Males (n=15, 23±2 yr, 84±21 kg, 176±7 cm) of average cardiorespiratory fitness (cycle VO2PEAK=38±9 ml·kg-1·min-1) participated in 3 heat trials (34.0±0.6°C, 41±3%RH, 3.6 km·hr-1) where they exercised at 70% VO2PEAK to volitional maximum on a cycle ergometer. During trials subjects consumed 2.5 g·kg-1 of 22°C water (room = RM), 4°C water (cold = CD), or -1°C water slushy (SL) every 10 min in a balanced crossover design. Exercise time (ExT), heart rate (HR), mean skin temperature (MTsk), rating of perceived exertion (RPE, 0-10), sweat rate (SR), and pre/post core temperature change (ΔTco) were measured. Subjects were blind to the measurement of ExT and its use with RPE as a dependent variable. One way (beverage) or two way (beverage x time) repeated measures ANOVA was used (α=0.05). RESULTS: ExT was not different between the trials (CD=34±9, SL=35±10, RM=31±9 min) but a trend was noted (p=0.0680) suggesting SL>RM. Supporting this trend was the fact that all subjects had their longest ExT on CD (n=10) or SL (n=5) trials. Neither ΔTco (CD=0.69±0.4, SL=0.64±0.4, RM=0.77±0.4°C) or SR (CD=1545±1108, SL=1837±691, RM=1890±489 ml·hr-1) differed between trials (p>0.05). As expected, a significant main effect for time was seen in HR, MTsk, and RPE where all three increased with exposure time (p=0.0001). No main effect for beverage was observed for either MTsk (CD=36.1±0.4, SL=36.0±0.4, RM=36.2±0.3°C) or RPE (CD=4.2±1.5, SL=4.5±2.0, RM=4.8±1.9), and no beverage x time interactions (p>0.05) were observed. A main effect for beverage was seen in HR (CD=157±16, SL=153±18, RM=160±17 bpm) where SL<RM (p=0.0007) and a trend towards a beverage x time interaction (p=0.0900) was noted. Likewise, HR at volitional maximum was different between the treatments (CD=168±20, SL=165±20, RM=173±20 bpm) where SL<RM (p=0.0170). Some of the subjects reported difficulty consuming the controlled volume in the SL treatment. CONCLUSION: While the controlled slushy consumption demonstrated slight performance improvements over the practical control (22°C water), its benefits over cold water (4°C) were not necessarily evident in this sample.