A common practice among endurance athletes is to train in hot environments for several weeks during a “heat stress camp,” with the intention of augmenting physiological stress and therefore metabolic adaptations to training. 1 Despite its widespread use, the effectiveness of combined exercise-heat
Ed Maunder, Andrew E. Kilding, Christopher J. Stevens and Daniel J. Plews
Fergus K. O’Connor, Steven E. Stern, Thomas M. Doering, Geoffrey M. Minett, Peter R. Reaburn, Jonathan D. Bartlett and Vernon G. Coffey
radiation (SR) exposure together with constant T a and RH elevates T sk , reduces the core-to-skin temperature gradient, and subsequently leading to decreased endurance capacity. Accordingly, each heat stress variable contributing to total heat strain may have individual effects with the potential to
Michael J. Zurawlew, Jessica A. Mee and Neil P. Walsh
Prior to exercise-heat stress, athletes and military personnel are advised to complete a period of heat acclimation to alleviate heat strain and improve exercise capacity in the heat. 1 The adaptive responses that improve exercise capacity in the heat include an earlier onset and an increase in
Scott J. Montain, Samuel N. Cheuvront and Henry C. Lukaski
Uncertainty exists regarding the effect of sustained sweating on sweat mineral-element composition.
To determine the effect of multiple hours of exercise-heat stress on sweat mineral concentrations.
Seven heat-acclimated subjects (6 males, 1 female) completed 5 × 60 min of treadmill exercise (1.56 m/s, 2% grade) with 20 min rest between exercise periods in 2 weather conditions (27 °C, 40% relative humidity, 1 m/s and 35 °C, 30%, 1 m/s). Sweat was collected from a sweat-collection pouch attached to the upper back during exercise bouts 1, 3, and 5. Mineral elements were determined by using inductively coupled plasma-emission spectrography.
At 27 °C, sweat sodium (863  µg/mL; mean [SD]), potassium (222  µg/mL), calcium (16 ) µg/mL), magnesium (1265  ng/mL), and copper (80  ng/mL) remained similar to baseline over 7 h of exercise-heat stress, whereas sweat zinc declined 42–45% after the initial hour of exercise-heat stress (Ex1 = 655 , Ex3 = 382 , Ex5 = 355  µg/mL, P < 0.05). Similar outcomes were observed for sweat zinc at 35 °C when sweat rates were higher. Sweat rate had no effect on sweat trace-element composition.
Sweat sodium, potassium, and calcium losses during multiple hours of sustained sweating can be predicted from initial sweat composition. Estimates of sweat zinc losses, however, will be overestimated if sweat zinc conservation is not accounted for in sweat zinc-loss estimates.
Andres E. Carrillo, René J. L. Murphy and Stephen S. Cheung
Prolonged physical exertion and environmental heat stress may elicit postexercise depression of immune cell function, increasing upper respiratory tract infection (URTI) susceptibility. We investigated the effects of acute and short-term vitamin C (VC) compared with placebo (PL) supplementation on URTI susceptibility, salivary immunoglobulin A (s-IgA), and cortisol responses in healthy individuals following prolonged exercise-heat stress.
Twelve participants were randomized into the VC or PL group in a double-blind design. For 12 days, participants consumed 3 × 500 mg tablets of VC or PL per day, with testing completed at baseline, then following acute (1 d) and short-term (8 d) supplementation. Participants performed 120.1 ± 49.6 min of cycling at 54 ± 6% VO2max in a hot (34.8 ± 1.0°C and 13 ± 3% relative humidity) environment, with saliva samples collected at pre-, post-, and 72 h postexercise. Health logs specifying URTI symptoms were completed for 7 days postexercise.
A 2 × 3 × 3 mixed ANOVA with a post hoc Bonferroni correction factor revealed a significant linear trend in postexercise cortisol attenuation in the VC group, 21.7 ± 15.1 nmol/L (mean ± SD) at baseline, to 13.5 ± 10.0 at acute, to 7.6 ± 4.2 after short term (P = .032). No differences were detected in ratio of s-IgA to protein or URTI symptoms between groups.
These data suggest that vitamin C supplementation can decrease postexercise cortisol in individuals performing exercise similar to that of a half-marathon or marathon in hot conditions. However, no changes in s-IgA and URTI were evident, possibly due to previous moderate training and reduced physical and psychological stress compared with athletes participating in ultramarathons.
Samantha K. Gill, Dean M. Allerton, Paula Ansley-Robson, Krystal Hemmings, Martin Cox and Ricardo J.S. Costa
The study aimed to determine if short-term high dose probiotic supplementation containing Lactobacillus casei (L.casei) attenuates the commonly reported exertional-heat stress (EHS) induced endotoxinaemia and cytokinaemia. Eight endurance trained male volunteers (mean± SD: age 26 ± 6 y, nude body mass 70.2 ± 8.8 kg, height 1.75 ± 0.05 m, VO2max 59 ± 5 ml·kg-1·min-1) completed a blinded randomized cross-over design, whereby oral ingestion of a commercially available probiotic beverage containing L.casei (volume equivalent for ×1011 colony forming units·day-1) (PRO) or placebo (PLA) was consumed for 7 consecutive days before exposure to EHS, which comprised of 2h running exercise at 60% VO2max in hot ambient conditions (34.0 °C and 32% RH). Blood samples were collected at baseline (7 days before EHS), pre-EHS, post-EHS (1 hr, 2 hr, 4 hr, and at 24 hr). Plasma samples were analyzed for gram-negative bacterial endotoxin, cytokine profile (IL-6, IL-1β, TNF-α, IFN-γ, IL-8, and IL-10) and plasma osmolality. Plasma osmolality did not differ between trials. Seven days of L.casei supplementation did not show significant changes in resting circulatory endotoxin concentration or plasma cytokine profile compared with PLA. A main effect of time was observed for IL-6, TNF-α, IL-10 and IL-8; whereby levels increased in response to EHS (p < .05). Relative to pre-EHS concentrations, higher plasma concentrations of endotoxin (p = .05), and a trend for higher plasma TNF-α concentration (p = .09) was observed on PRO compared with PLA throughout recovery. Short-term high dose supplementation of a probiotic beverage containing L.casei before EHS did not attenuate EHS induced endotoxaemia and cytokinaemia; nor is it more positively favorable over a placebo.
Paola Rodriguez-Giustiniani and Stuart D.R. Galloway
and to establish the workload at which each individual exercised during the exercise-heat stress experimental trials (moderate intensity, calculated to be approximately 60% of VO 2max for each subject). Experimental Trials Each individual participated in three experimental trials: the first was
Samantha Kirsty Gill, Ana Maria Teixeira, Fatima Rosado, Martin Cox and Ricardo Jose Soares Costa
The study aimed to determine whether high-dose probiotic supplementation containing Lactobacillus casei (L. casei) for 7 consecutive days enhances salivary antimicrobial protein (S-AMP) responses to exertional–heat stress (EHS). Eight endurance-trained male volunteers (age 26 ± 6 years, nude body mass 70.2 ± 8.8 kg, height 1.75 ± 0.05 m, VO2max 59 ± 5 ml·kg-1·min-1 [M ± SD]) completed a blinded randomized and counterbalanced crossover design. Oral supplementation of the probiotic beverage (PRO; L. casei × 1011 colony-forming units·day-1) or placebo (PLA) was consumed for 7 consecutive days before 2 hr running exercise at 60% VO2max in hot ambient conditions (34.0 °C and 32% RH). Body mass and unstimulated saliva and venous blood samples were collected at baseline (7 days before EHS), pre-EHS, post-EHS (1 hr, 2 hr, and 4 hr), and at 24 hr. Saliva samples were analyzed for salivary (S) IgA, α-amylase, lysozyme, and cortisol. Plasma samples were analyzed for plasma osmolality. Body mass and plasma osmolality did not differ between trials. Saliva flow rate remained relatively constant throughout the experimental design in PRO (overall M ± SD = 601 ± 284 μ1/min) and PLA (557 ± 296 μl/min). PRO did not induce significant changes in resting S-AMP responses compared with PLA (p > .05). Increases in S-IgA, S-α-amylase, and S-cortisol responses, but not S-lysozyme responses, were observed after EHS (p < .05). No main effects of trial or Time × Trial interaction were observed for S-AMP and S-cortisol responses. Supplementation of a probiotic beverage containing L. casei for 7 days before EHS does not provide any further oral–respiratory mucosal immune protection, with respect to S-AMP, over PLA.
Christopher John Stevens, Megan L. Ross, Julien D. Périard, Brent S. Vallance and Louise M. Burke
, Cheuvront SN , Palombo LJ , Goodman DA , Sawka MN . Prior heat stress: effect on subsequent 15-min time trial performance in the heat . Med Sci Sports Exerc . 2009 ; 41 ( 6 ): 1311 – 1316 . PubMed ID: 19461533 doi:10.1249/MSS.0b013e3181988c14 10.1249/MSS.0b013e3181988c14 19461533 5. Racinais
Bob Murray, John Stofan and Bob Sallis
This article summarizes a case of ischemic colitis suffered by a triathlete during an Ironman competition.
Exercise results in a significant reduction in splanchnic blood flow to help maintain cardiovascular function. When dehydration and heat stress accompany exercise, blood flow to the splanchnic vasculature is further reduced, increasing the risk of local ischemia and tissue injury.
Ischemic colitis caused by dehydration and heat stress.
Right hemicolectomy involving a 16-cm segment of ischemic large intestine and appendectomy the day following the race.
This case study highlights one of the risks associated with dehydration during prolonged exercise in the heat. Of particular interest are practical interventions to reduce health and performance issues.
Poor hydration and nutrition practices during intense exercise can affect gut function, impair performance, and jeopardize health. Optimal intake of fluid, carbohydrate, and salt will enhance performance and reduce risk to health.