Partial and Complete Fluid Replacement Maintains Exercise Performance in a Warm Environment Following Prolonged Cold-Water Immersion

Special warfare operators may be exposed to prolonged immersion before beginning a land-based mission. This immersion will result in substantial hypohydration because of diuresis. This study tested the hypothesis that both partial and full postimmersion rehydration would maintain performance during exercise in the heat. Seven men (23 +/- 2 years; Vo(2max): 50.8 +/- 5.3 ml<middle dot>kg(-1)<middle dot>min(-1)) completed a control trial (CON) without prior immersion and 3 immersion (18.0 degrees C) trials without rehydration (NO) or with partial (HALF) or full (FULL) rehydration. After immersion, subjects completed a 60-minute weighted ruck march (20.4 kg; 5.6 kph) and a 15-minute intermittent exercise protocol (iEPT) in a warm environment (30.0 degrees C and 50.0% relative humidity). The primary outcome was distance (km) covered during the iEPT. A priori statistical significance was set to p <= 0.05. Immersion resulted in 2.3 +/- 0.4% loss of body mass in all immersion trials (p < 0.01). Distance covered during the first 13-minute interval run portion of iEPT was reduced in the NO rehydration trial (1.59 +/- 0.18 km) compared with all other conditions (CON: 1.88 +/- 0.18 km, p = 0.03; HALF: 1.80 +/- 0.18 km, p < 0.01; FULL: 1.86 +/- 0.28 km, p = 0.01). During the final 2 minutes of the iEPT, distance in the NO rehydration trial (0.31 +/- 0.07 km) was reduced compared with the FULL rehydration trial (0.37 +/- 0.07 km; p < 0.01) but not compared with CON (0.35 +/- 0.07 km; p = 0.09) or HALF (0.35 +/- 0.07 km; p = 0.08). Both partial and full postimmersion fluid replacement maintained intermittent exercise performance and should be applied as rehydration strategies.