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No Effect of 5% Hypohydration on Running Economy of Competitive Runners at 23°C

ARMSTRONG, LAWRENCE E.1; WHITTLESEY, MICHAEL J.2; CASA, DOUGLAS J.1; ELLIOTT, TABATHA A.1; KAVOURAS, STAVROS A.3; KEITH, NICOLE R.4; MARESH, CARL M.1

Medicine & Science in Sports & Exercise: October 2006 - Volume 38 - Issue 10 - pp 1762-1769
doi: 10.1249/01.mss.0000230123.68394.ff
BASIC SCIENCES: Original Investigations

Purpose: Although running economy (RE) is recognized as an integral component of successful endurance performance and is affected by numerous factors, little is known about the influence of body water loss on RE. This investigation examined the effects of hypohydration (HY) on RE and associated physiological responses.

Methods: Ten highly trained collegiate distance runners (mean ± SD; age, 20 ± 3 yr; height, 178.5 ± 6.3 cm; body mass, 66.7 ± 5.4 kg; V˙O2max, 66.5 ± 4.1 mL·kg−1·min−1) participated in four experiments on separate days, twice in a euhydrated (EU) and twice in a HY state (−5.5 and −5.7% body mass loss achieved during 24 h). At each hydration level, subjects performed one 10-min treadmill run per day (23°C environment), at either 70% V˙O2max (EU 70% or HY 70%) or 85% V˙O2max (EU 85% or HY 85%) in a randomized, repeated-measures design. Cardiopulmonary, metabolic, thermal, hormonal, and perceptual variables were measured.

Results: No between-treatment differences existed for RE (EU 70%, 46.3 ± 3.2; HY 70%, 47.2 ± 3.8; EU 85%, 58.6 ± 2.8; HY 85%, 58.9 ± 4.1 mL·kg−1·min−1), postexercise plasma lactate concentration (EU 70%, 1.9 ± 0.6; HY 70%, 1.8 ± 0.6; EU 85%, 6.5 ± 3.5; HY 85%, 6.4 ± 3.5 mmol·L−1), or rating of perceived exertion. HY resulted in a greater (P < 0.05 to 0.001) heart rate (HR), rectal temperature, and plasma norepinephrine concentration (NE), concurrent with reduced cardiac output, stroke volume, and respiratory exchange ratio.

Conclusion: HY did not alter the RE or lactate accumulation of endurance athletes during 10 min of exercise at 70 and 85% V˙O2max. These findings indicate that HY had no effect on RE, but that it increased physiological strain in a 23°C environment.

1Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, CT; 2Department of Athletics, University of North Carolina, Chapel Hill, NC; 3Department of Nutrition and Dietetics, Harokopio University, Athens, GREECE; 4Indiana University, Purdue University at Indianapolis, Indianapolis, IN

Address for correspondence: Lawrence E. Armstrong, Ph.D., F.A.C.S.M., University of Connecticut, Human Performance Laboratory, Department of Kinesiology, Unit 1110, 2095 Hillside Road, Storrs, CT 06269-1110; E-mail: lawrence.armstrong@uconn.edu.

Submitted for publication November 2005.

Accepted for publication May 2006.

©2006The American College of Sports Medicine