Purpose: The aim of this study was to quantify changes in brain volume after exercise/heat-induced hypohydration in man.
Methods: Eight active men completed intermittent exercise in a warm environment, until 2.9% ± 0.1% of body mass was lost. Subjects remained hypohydrated for 2 h after the end of exercise. Brain volume was measured before, immediately after, and 1 and 2 h after exercise using magnetic resonance imaging (Philips 3T Achieva, AE Eindhoven, The Netherlands). Measures of subjective feelings and core body temperature were also monitored. Blood samples were drawn to determine serum electrolyte concentrations and osmolality and to allow calculation of changes in blood and plasma volumes.
Results: Brain volume was not influenced by hypohydration (0.2% ± 0.4%; effect size (ES) = 0.2, P = 0.310). Reductions in ventricular (4.0% ± 1.8%; ES = 4.6, P < 0.001) and cerebrospinal fluid (3.1% ± 1.9%; ES = 3.3, P = 0.003) volumes were observed after exercise. Compared with preexercise levels, serum osmolality was elevated throughout the 2-h postexercise period (+10 ± 2 mOsm·kg−1, P < 0.001). Core temperature increased from 37.1°C ± 0.3°C at rest to 39.3°C ± 0.5°C at the end of exercise (P = 0.001).
Conclusions: These data demonstrate that brain volume remains unchanged in response to moderate hypohydration and presence of serum hyperosmolality, suggesting that mechanisms are in place to defend brain volume.
1School of Sport, Exercise and Health Sciences, Loughborough University, Leicestershire, UNITED KINGDOM; 2Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, UNITED KINGDOM; and 3Brain and Body Centre, School of Psychology, University of Nottingham, Nottingham, UNITED KINGDOM
Address for correspondence: Ronald J. Maughan, Ph.D., School of Sport and Exercise Sciences, Loughborough University, Leicestershire, LE11 3TU, United Kingdom; E-mail: firstname.lastname@example.org.
Submitted for publication October 2009.
Accepted for publication April 2010.