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      Skeletal muscle volume following dehydration induced by exercise in heat

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          Abstract

          Background

          Intracellular skeletal muscle water is redistributed into the extracellular compartment during periods of dehydration, suggesting an associated decline in muscle volume. The purpose of this study was to evaluate skeletal muscle volume in active (knee extensors (KE)) and less active (biceps/triceps brachii, deltoid) musculature following dehydration induced by exercise in heat.

          Methods

          Twelve participants (seven men, five women) cycled in the heat under two conditions: (1) dehydration (DHYD) resulting in 3% and 5% losses of estimated total body water ( ETBW), which was assessed by changes in body mass, and (2) fluid replacement (FR) where 3% and 5% losses of ETBW were counteracted by intermittent (20 to 30 min) fluid ingestion via a carbohydrate-electrolyte beverage. During both conditions, serum osmolality and skeletal muscle volume (assessed by magnetic resonance imaging) were measured at baseline and at the 3% and 5% ETBW loss measurement points.

          Results

          In DHYD, serum osmolality increased at 3% ( p = 0.005) and 5% ( p < 0.001) ETBW losses, while FR decreased serum osmolality at the 5% loss of ETBW time point ( p = 0.009). In DHYD, KE muscle volume declined from 1,464 ± 446 ml to 1,406 ± 425 ml (3.9%, p < 0.001) at 3% ETBW loss and to 1,378 ± 421 ml (5.9%, p < 0.001) at 5% ETBW loss. The largest decline in KE volume in DYHD occurred in the mid-belly (31 ml, p = 0.001) and proximal (24 ml, p = 0.001) regions of the grouped vasti muscles. There were no changes in volume for the biceps/triceps ( p = 0.35) or deltoid ( p = 0.92) during DHYD. FR prevented the loss of KE muscle volume at 3% (1,430 ± 435 ml, p = 0.074) and 5% (1,431 ± 439 ml, p = 0.156) ETBW loss time points compared to baseline (1,445 ± 436 ml).

          Conclusions

          Following exercise in the heat, the actively contracting muscles lost volume, while replacing lost fluids intermittently during exercise in heat prevented this decline. These results support the use of muscle volume as a marker of water loss.

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          Most cited references35

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              Chronic mild dehydration is a common condition in some population groups, including especially the elderly and those who participate in physical activity in warm environments. Hypohydration is recognised as a precipitating factor in a number of acute medical conditions in the elderly, and there may be an association, although not necessarily a causal one, between a low habitual fluid intake and some cancers, cardiovascular disease and diabetes. There is some evidence of impairments of cognitive function at moderate levels of hypohydration, but even short periods of fluid restriction, leading to a loss of body mass of 1-2%, lead to reductions in the subjective perception of alertness and ability to concentrate and to increases in self-reported tiredness and headache. In exercise lasting more than a few minutes, hypohydration clearly impairs performance capacity, but muscle strength appears to be relatively unaffected.
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                Author and article information

                Contributors
                Journal
                Extrem Physiol Med
                Extrem Physiol Med
                Extreme Physiology & Medicine
                BioMed Central
                2046-7648
                2012
                4 September 2012
                : 1
                : 3
                Affiliations
                [1 ]Department of Exercise Science, Syracuse University, 820 Comstock Ave, Room 201Women’s Building, Syracuse, NY, 13244, USA
                [2 ]Present address: Wyle Integrated Science and Engineering, Exercise Physiology and Countermeasures Project, Houston, TX, 77058, USA
                [3 ]Department of Kinesiology, University of New Hampshire, 124 Main Street, Durham, NH, 03824, USA
                [4 ]School of Chiropractic and Sports Science, Murdoch University, 90 South Street, Murdoch, WA, 6150, Australia
                [5 ]Universities Space and Research Association, Exercise Physiology and Countermeasures Project, NASA Lyndon B Johnson Space Center, 2101 NASA Parkway, SK/261, Houston, TX, 77058, USA
                Article
                2046-7648-1-3
                10.1186/2046-7648-1-3
                3707098
                23849266
                6fce869c-5c93-408c-9407-2338b89eca03
                Copyright ©2012 Stormo et al.; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 7 February 2012
                : 4 September 2012
                Categories
                Research

                dehydration,skeletal muscle,mri,cycling,total body water,fluid shift

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