The Role Of Rehydration Beverage Type On Ruck Performance In The Heat Following Cold-water Immersion

Warfighters performing transport dives experience hypohydration due to immersion diuresis. Aerobic performance suffers when total water loss exceeds 2% of body mass, especially in warm environments. PURPOSE: To investigate if drinking water (W), carbohydrate solution (CHO), or carbohydrate and electrolyte solution (CHO + E) would maintain performance after immersion induced dehydration. METHODS: Six males (25 ± 2y, BF: 12.6 ± 5.1%, BM: 79.8 ± 5.8 kg, VO2max: 50.4 ± 6.2 ml·kg-1·min-1) performed three, 4-hour cold-water immersions (18.0 ± 0.2 °C) and one non-immersed control trial (NI). After exiting the water, participants completed a 60 min weighted (20.4 kg) ruck march at 55% VO2max in a warm environment (29.4 ± 0.2 °C, 51.7 ± 2.4%RH) during which they consumed W, CHO (6.5% glucose), or CHO + E (50 mmol/L NaCl) equal to 100% of fluids lost. AT the beginning, midpoint, and end of the ruck, rating of perceived exertion (RPE), thermal comfort (C), oxygen consumption (VO2) were collected, and movement economy (ME) was calculated. Heart rate (HR) and core temperature (Tc) were collected. Nude body mass was taken before and after immersion. RESULTS: Participants experienced a decrease in Tc (W:0.52 ± 0.08 °C, CHO:0.56 ± 0.3 °C p < 0.05, CHO + E:0.49 ± 0.05 °C, p < 0.01) and HR (W:13 ± 4 bpm; CHO:14 ± 11 bpm; CHO + E:14 ± 7 bpm, all p < 0.05) during immersion. HR and Tc increased during the ruck (p < 0.001). BM loss from immersion was >2% (p < 0.01) for all conditions (W:2.5 ± 0.8%; CHO:2.5 ± 0.4%; CHO + E:2.5 ± 0.7%). ME and VO2 were higher in W (p < 0.001) but not in CHO or CHO + E compared to NI. ME and VO2 were also higher between W than CHO and CHO + E (p < 0.01) but not different between CHO and CHO + E. No differences were found for RPE, RER, HR, or C across any intervention compared to NI. CONCLUSIONS: CHO and CHO + E solutions improved performance compared to water during a 60-min weighted ruck following immersion when hydration was equal to body mass loss.