No effect of 5% hypohydration on running economy of competitive runners at 23 degrees C.
OBJECTIVE
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; VO2max, 66.5 +/- 4.1 mL x kg(-1) x 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 degrees C environment), at either 70% VO2max (EU 70% or HY 70%) or 85% VO2max (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 x kg(-1) x 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 x 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.


CONCLUSIONS
HY did not alter the RE or lactate accumulation of endurance athletes during 10 min of exercise at 70 and 85% VO2max. These findings indicate that HY had no effect on RE, but that it increased physiological strain in a 23 degrees C environment.
Armstrong
Lawrence E
LE
Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, CT 06269-1110, USA. lawrence.armstrong@uconn.edu
Whittlesey
Michael J
MJ
Casa
Douglas J
DJ
Elliott
Tabatha A
TA
Kavouras
Stavros A
SA
Keith
Nicole R
NR
Maresh
Carl M
CM
D000293:Adolescent; D000328:Adult; D001775:Blood Circulation; D001831:Body Temperature; D001834:Body Water; D003163:Competitive Behavior / Q000502:physiology*; D003681:Dehydration / Q000503:physiopathology*; D005080:Exercise Test; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D009638:Norepinephrine; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D011446:Prospective Studies; D012420:Running / Q000502:physiology*; D011795:Surveys and Questionnaires; D013997:Time Factors
D009638:Norepinephrine