Samuel N Cheuvront

..This can usually be achieved with fluid intakes of under 1 L x h(-1)...

..These observations suggest that hypohydration and prior heat stress are associated with greater reductions in CBFV with greater CVR, which likely contribute to orthostatic intolerance...

..The recent generation of a nomogram that predicts changes in finishing time consequent to changes in weather conditions offers runners and coaches a tool for use in developing marathon race strategy...

..Marathon running performance slows in warm weather conditions, but the quantitative impact of weather has not been established...

..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...

..Recommendations are provided to individualise fluid intakes with the goal of preventing excessive dehydration (>2% body mass) as well as weight gain. The minor importance of 'matters of debate' to fluid replacement is also discussed...

..This study examined the effects of hypohydration and moderate hyperthermia (core temperature elevation) on anaerobic exercise performance in a temperate environment...

..Because men possess a larger aerobic capacity and greater muscular strength, the gap in running performances between men and women is unlikely to narrow naturally...

..05). SR was higher (P < 0.05) in P and S versus B, but the magnitude of differences was small. A protective vest increases physiological strain independent of added load, while a spacer garment does not alter this outcome...

..05). These data demonstrate that 1) HYP impairs endurance exercise performance in temperate but not cold air but 2) cold stress per se does not...

..BC did not alter time-trial performance, cognitive performance, mood, perceived exertion, or perceived thermal comfort. We conclude that BCAA does not alter exercise or cognitive performance in the heat when subjects are hypohydrated...

..However, the explanatory power of exercise with marked environmental heat stress on the appearance of S-100beta is questionable. It is possible that the process of heat acclimation might afford additional insight...

..The purpose of this review is to evaluate the scientific merit of the Zone Diet and its health claims in an effort to help delineate what is and what is not sound nutrition science...

..These findings indicate that the IRC approach to MCC is a more efficient means of cooling when compared with CC paradigms and can improve MCC capacity by reducing power requirements...

..05), but not HW. These results indicate that BVS(On) reduces physiological strain in all three environments by a similar amount; however, in hot-dry conditions the BVS(Off) increases physiological strain...

..m(-2)) ( p < 0.05). These findings suggest that IC provided a favourable skin to LCG gradient for heat dissipation by conduction and reduced heat strain comparable to CC during exercise-heat stress in chemical protective clothing...

..The impact of prior heat stress on subsequent aerobic exercise-heat performance has not been studied...

..05) or the self-selected pacing strategy employed. These findings indicate that the nutritional adenosine receptor antagonists caffeine and quercetin do not enhance endurance exercise performance during compensable heat stress...

..Our observation that runners were able to sustain running velocity despite T(re) >40 degrees C is evidence against 40 degrees C representing a "critical" core temperature limit to performance...

..Dehydration augments hyperthermia and plasma volume reductions, which combine to accentuate cardiovascular strain and reduce Vo(2max). Importantly, the negative performance consequences of dehydration worsen as T(sk) increases...

..Rater and SReg were not different by conventional t-test (P > 0.05). SReg provides a simple, valid, and standardized way to determine sweating threshold temperature and sweating sensitivity values for thermoregulatory studies...

..changes in SR. These findings provide a quantitative basis for study design and optimization of power/sample size analysis in the evaluation of thermoregulatory sweating...

..Moderate HYP had no effect on cognitive and psychomotor performance in either environment, cold exposure produced equivocal effects, and aerobic exercise improved some aspects of military task performance...

..This study examined the impact of 10 d of exercise-heat acclimation on sweat mineral concentrations...

..A secondary purpose was to validate use of the tool by dehydrating a group of volunteers...

..These data demonstrate that physiological adaptations in humans undergoing HA are accompanied by both increases in baseline levels and changes in regulation of cytoprotective HSPs...

..Environmental heat stress degrades aerobic performance; however, little research has focused on performance when the selected task elicits modest elevations in core body temperature (<38.5 degrees C)...

..Salivary osmolality (Sosm) is a potentially useful hydration marker but may be confounded by oral artifacts...

..Neither prediction equation provided accurate estimates of TSL in warm or cool conditions for women runners. These results illustrate the difficulty of accurately estimating and predicting sweat losses in the field...

..07). In conclusion, hypohydration at 3,048 m 1) degrades aerobic performance in an additive manner with that induced by ALT; and 2) did not appear to increase the prevalence/severity of AMS symptoms...

..The data also suggest that daily BM is a sufficiently stable physiological parameter for potential daily fluid balance monitoring...

..Uncertainty exists regarding the effect of sustained sweating on sweat mineral-element composition...

..05). In conclusion, this study demonstrates the failure to improve jump height when HYP can be explained by offsetting reductions in both VGRI and body mass...

..Well-recognized markers for static (one time) or dynamic (monitoring over time) dehydration assessment have not been rigorously tested for their usefulness in clinical, military, and sports medicine communities...

..The use of caffeine supplements in athletic and military populations has increased in recent years. Excessive caffeine consumption in conjunction with exercise in a hot environment may predispose individuals to heat illness...

..In order to gain insight into IRC mechanisms, a mathematical model was developed to simulate thermal interaction between the human and IRC...

..05). The two methodologies appear to produce similar P (osm) values when measured in most individuals. However, the potential for significant dilution (>3 mmol/kg) should be considered when choosing the pre-hydration methodology...

..7 L for adult women meets the needs of the vast majority of persons. However, strenuous physical exercise and heat stress can greatly increase daily water needs, and the individual variability between athletes can be substantial...

..The combined challenge of exercise and environment associated with marathon running can substantially challenge the human thermoregulatory system...

..g., under fingernails, on arm hair), then decrease with extended sweating and approach those measured from the scapular region...

..DEET can be safely worn during military, occupational and recreational activities in hot, insect infested environments...

..However, the effect of elapsed time between ITS ingestion and T int measurement has not been thoroughly studied...

..This information can be found in anecdotal reports, authoritative reference books for runners, and scientific publications alike, but it lacks a comprehensive review...

..Serious heat illness has received considerable recent attention due to catastrophic heat waves in the United States and Europe, the deaths of high-profile athletes, and military deployments...

..Warmer weather negatively impacts the finishing time of slower marathon (42.2 km) runners more than faster runners. How warmer weather impacts runners' regulation of effort (pacing) leading to the decreased performance is poorly understood...

..S. Army. It is known that prior infection is a risk factor for heat illness and some of the 37 heat stroke deaths cited infections (eg, pneumonia, influenza) in the medical records...

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..These results suggest a possible iron conservation that prevents excessive iron loss during prolonged exercise...

..Intravenous fluid replacement after exercise has been investigated to a lesser extent and its role for fluid replacement in the dehydrated but otherwise well athlete remains equivocal...