Sodium-Facilitated Hypervolemia, Endurance Performance, and Thermoregulation

M. G. Coles; M. J. Luetkemeier

doi:10.1055/s-2004-820989

International Journal of Sports Medicine, Table of Contents

Int J Sports Med 2005; 26(3): 182-187
DOI: 10.1055/s-2004-820989

Physiology & Biochemistry

Sodium-Facilitated Hypervolemia, Endurance Performance, and Thermoregulation

M. G. Coles¹ , M. J. Luetkemeier¹

¹University of Utah, Salt Lake City, Utah, USA

Abstract

The purpose of this study was to investigate the effects of an immediate pre-exercise, orally ingested, sodium load (164 mEq Na⁺) (IPOSL), equivalent to 10 ml per kilogram of body weight, on plasma volume, endurance performance, and thermoregulation. Fourteen male participants consumed a nearly isotonic (255 mOsm · kg^-1) IPOSL and a hypotonic (94 mOsm · kg^-1), no-sodium, placebo beverage (Pl) equivalent to 10 ml · kg^-1 body weight in a randomized design. Subjects cycled at 70 % of maximal work rate, in a 21.0 - 23.3 °C lab, for 45 min while cardiovascular and thermoregulatory variables were measured. This was followed by a 15-min performance time trial. IPOSL and Pl ingestion lead to a 3.1 % expansion and a 4.7 % reduction in resting baseline plasma volume, respectively. IPOSL maintained plasma volume during exercise to a greater extent than the Pl at 15 and 30, but not 45 min. There was a significant improvement (≈ 7.8 %; p < 0.05) in time trial performance following IPOSL. No significant differences were observed for heart rate, core temperature, rate of perceived exertion or total body sweat rate (p > 0.05). In conclusion, IPOSL ingestion increased pre-exercise plasma volumes, maintained 15- and 30-min exercise plasma volumes, and improved an endurance performance time trial better than the Pl with no apparent compromise in thermoregulation.

Key words

Plasma volume - urine and plasma osmolality - core temperature - body weight loss

Full Text

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M. Coles

California State University, Fresno, Department of Kinesiology

5275 N. Campus Dr. M/S SG28

Fresno 93740

California

USA

Phone: + 5592784166

Fax: + 55 92 78 70 10

Email: mcoles@csufresno.edu