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Evaluation of the limits to accurate sweat loss prediction during prolonged exercise

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Abstract

Sweat prediction equations are often used outside their boundaries to estimate fluid requirements and generate guidance. The limitations associated with these generalized predictions have not been characterized. The purposes of this study were to: (1) evaluate the accuracy of a widely used sweat prediction equation (SHAP) when widening it’s boundaries to include cooler environments (2 h) and very prolonged exercise (8 h), (2) determine the independent impact of holding skin temperature constant (SHAP36), and (3) describe how adjustments for non-sweat losses (NSL) and clothing saturation dynamics affect prediction accuracy. Water balance was measured in 39 volunteers during 15 trials that included intermittent treadmill walking for 2 h (300–600 W, 15–30°C; n = 21) or 8 h (300–420 W, 20–40°C; n = 18). Equation accuracy was assessed by comparing actual and predicted sweating rates (211 observations) using least-squares regression. Mean and 95% confidence intervals for group differences were compared against a zone of indifference (±0.125 l/h). Sweating rate variance accounted for by SHAP and SHAP36 was always high (r 2 > 0.70), while the standard error of the estimate was small and uniform around the line of best fit. SHAP errors were >0.125 l/h during 2 and 8 h of exercise. SHAP36 errors were <0.125 l/h for 2 h conditions but were higher at 8 h in three of the six warmest trials. Adjustments for NSL and clothing saturation dynamics help explain SHAP errors at 2 and 8 h, respectively. These results provide a basis for future development of accurate algorithms with broader utility.

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Acknowledgments

The authors wish to thank the many people who provided essential assistance on this study including, but not limited to, Erik Lloyd, Kaye Brownlee, Laurie Bronson, Leslie Levine, Rob Demes, Walida Leammukda, Carrie Vernieuw, Scott Robinson, Lou Stephenson, Bruce Cadarette, Matt Ely, Lenny Souza and Lenny Elliott. The view, opinions, and/or findings contained in this report are those of the authors and should not be construed as an official Department of the Army position, or decision, unless so designated by other official documentation. Approved for public release; distribution unlimited. This work was funded in part by a congressional grant (033015) from the US Army Medical Research and Materiel Command Peer Reviewed Medical Research Program (MRMC PRMRP).

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Correspondence to Samuel N. Cheuvront.

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Cheuvront, S.N., Montain, S.J., Goodman, D.A. et al. Evaluation of the limits to accurate sweat loss prediction during prolonged exercise. Eur J Appl Physiol 101, 215–224 (2007). https://doi.org/10.1007/s00421-007-0492-x

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  • DOI: https://doi.org/10.1007/s00421-007-0492-x

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