Influence of Hydration Status on Thermoregulation and Cycling Hill Climbing

Tammie R. Ebert, David T. Martin, Nicola Bullock, I??igo Mujika, Marc J. Quod, Lesley A. Farthing, Louise M. Burke, Robert T. Withers
2007 Medicine & Science in Sports & Exercise  
Purpose: Although dehydration can impair endurance performance, a reduced body mass may benefit uphill cycling by increasing the power-to-mass ratio. This study examined the effects of a reduction in body mass attributable to unreplaced sweat losses on simulated cycling hill-climbing performance in the heat. Methods: Eight well-trained male cyclists (mean T SD: 28.4 T 5.7 yr; 71.0 T 5.9 kg; 176.7 T 4.7 cm; V O 2peak : 66.2 T 5.8 mLIkg j1 Imin j1 ) completed a maximal graded cycling test on a
more » ... tionary ergometer to determine maximal aerobic power (MAP). In a randomized crossover design, cyclists performed a 2-h ride at 53% MAP on a stationary ergometer, immediately followed by a cycling hill-climb time-to-exhaustion trial (88% MAP) on their own bicycle on an inclined treadmill (8%) at approximately 30-C. During the 2-h ride, they consumed either 2.4 L of a 7% carbohydrate (CHO) drink (HIGH) or 0.4 L of water (LOW) with sport gels to match for CHO content. Results: After the 2-h ride and before the hill climb, drinking strategies influenced body mass (LOW j2.5 T 0.5% vs HIGH 0.3 T 0.4%; P G 0.001), HR (LOW 158 T 15 vs HIGH 146 T 15 bpm; P = 0.03), and rectal temperature (T re : LOW 38.9 T 0.2 vs HIGH 38.3 T 0.2-C; P = 0.001). Despite being approximately 1.9 kg lighter, time to exhaustion was significantly reduced by 28.6 T 13.8% in the LOW treatment (LOW 13.9 T 5.5 vs HIGH 19.5 T 6.0 min, P = 0.002), as was the power output for a fixed speed (LOW 308 T 28 vs HIGH 313 T 28 W, P = 0.003). At exhaustion, T re was higher in the LOW treatment (39.5 vs HIGH 39.1-C; P G 0.001), yet peak HR, blood lactate, and glucose were similar. Conclusion: Exercise-induced dehydration in a warm environment is detrimental to laboratory cycling hill-climbing performance despite reducing the power output required for a given speed.
doi:10.1249/01.mss.0000247000.86847.de pmid:17277597 fatcat:gj3p4qxuwjeynkvdeegf4hnrou