The Effects Of Mode Of Rehydration On Stress Hormone Respsonse To Subsequent Maximal Intensity Exercise In The Heat.

PURPOSE: Endocrine response to strenuous exercise in the heat can serve as an indicator of the amount of strain the body is experiencing. Previous intravenous (IV) versus oral rehydration studies found no difference cortisol (CORT) response between modes of rehydration, but mixed norepinephrine (NOR) response with ORAL during an exercise-heat challenge (EHC). The purpose of this study was to examine the effects of mode of rehydration on the stress-hormone response to a subsequent EHC that more closely mimics a real-life athletic situation utilizing three traditional modes of rehydration ad libitum (ADL), IV and ORAL and combined half IV and half ORAL (I+O) fluids of identical volume. METHODS: Ten healthy, non-smoking, active men (age 23.3 ± 1.1 y; height, 177.8 ± 2.8 cm; body mass, 81.4 ± 1.3 kg; body fat, 11.0 ± 1.0%; O2max, 58.8 ± 1.3 ml·kg-1·min-1) completed four trials consisting of dehydration by -4% body mass, rehydration to -2% body mass, and an EHC comprised of 25 min of running at 60% O2max, a maximal effort 0.5 mile run, five minutes of rest and five min of self-paced repetitive box lifting (RBL). Plasma catecholamines [epinephrine (EPI) and NOR] and CORT were analyzed at baseline, post-exercise dehydration, immediately before EHC (EHCPRE), immediately-post 0.5 mile run (EHC30), immediately-post RBL (EHCIP), and 15 minutes post-RBL. Data was analyzed with a two-way repeated measures ANOVA or Student’s t-test, p< 0.05. RESULTS: Catecholamine response was not significantly different between modes of rehydration, but significantly increased during EHC (EHCPRE - EPI 0.52±0.44 pmol·L-1, NOR 2.64±0.89 nmol·L-1; EHC30 - EPI 3.59±1.89 pmol·L-1, NOR 21.66±7.42 nmol·L-1; EHCIP - EPI 1.31±0.84 pmol·L-1, NOR 15.45±6.63 nmol·L-1). CORT response was significantly lower during I+O (EHCPRE: 451.8±118.5 nmol·L-1, EHCIP 505.4±237.9 nmol·L-1) compared to all other trials (EHCPRE 567.1±240.5 nmol·L-1, EHCIP - 603.6±270.1 nmol·L-1). CONCLUSIONS: These results suggest a synergistic effect of I+O on plasma CORT concentration resulting in reduced adreno-cortical response. It is possible the I+O treatment resulted in reduced hormonal response or increased removal rate due to a combination of oropharyngeal response and rapid plasma volume restoration since stress was controlled across conditions.