Influence of hydration status on thermoregulation and cycling hill climbing.
OBJECTIVE
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 +/- SD: 28.4 +/- 5.7 yr; 71.0 +/- 5.9 kg; 176.7 +/- 4.7 cm; VO2peak: 66.2 +/- 5.8 mL x kg(-1) x min(-1)) completed a maximal graded cycling test on a stationary 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 degrees 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 -2.5 +/- 0.5% vs HIGH 0.3 +/- 0.4%; P < 0.001), HR (LOW 158 +/- 15 vs HIGH 146 +/- 15 bpm; P = 0.03), and rectal temperature (T(re): LOW 38.9 +/- 0.2 vs HIGH 38.3 +/- 0.2 degrees C; P = 0.001). Despite being approximately 1.9 kg lighter, time to exhaustion was significantly reduced by 28.6 +/- 13.8% in the LOW treatment (LOW 13.9 +/- 5.5 vs HIGH 19.5 +/- 6.0 min, P = 0.002), as was the power output for a fixed speed (LOW 308 +/- 28 vs HIGH 313 +/- 28 W, P = 0.003). At exhaustion, T(re) was higher in the LOW treatment (39.5 vs HIGH 39.1 degrees C; P < 0.001), yet peak HR, blood lactate, and glucose were similar.


CONCLUSIONS
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.
Ebert
Tammie R
TR
Department of Physiology, Australian Institute of Sport, Canberra, Australia. tammie.ebert@ausport.gov.au
Martin
David T
DT
Bullock
Nicola
N
Mujika
Iñigo
I
Quod
Marc J
MJ
Farthing
Lesley A
LA
Burke
Louise M
LM
Withers
Robert T
RT
D000328:Adult; D000531:Altitude; D001642:Bicycling / Q000502:physiology*; D015992:Body Mass Index; D001833:Body Temperature Regulation; D003681:Dehydration; D005080:Exercise Test; D005221:Fatigue / Q000150:complications / Q000503:physiopathology; D006304:Health Status; D006339:Heart Rate; D006801:Humans; D008297:Male; D010807:Physical Endurance / Q000502:physiology*; D011446:Prospective Studies