1.
Ice slurry on outdoor running performance in heat.
Yeo, ZW, Fan, PW, Nio, AQ, Byrne, C, Lee, JK
International journal of sports medicine. 2012;(11):859-66
Abstract
The efficacy of ingestion of ice slurry on actual outdoor endurance performance is unknown. This study aimed to investigate ice slurry ingestion as a cooling intervention before a 10 km outdoor running time-trial. Twelve participants ingested 8 g · kg (- 1) of either ice slurry ( - 1.4°C; ICE) or ambient temperature drink (30.9°C; CON) and performed a 15-min warm-up prior to a 10 km outdoor running time-trial (Wet Bulb Globe Temperature: 28.2 ± 0.8°C). Mean performance time was faster with ICE (2 715 ± 396 s) than CON (2 730 ± 385 s; P=0.023). Gastrointestinal temperature (Tgi) reduced by 0.5 ± 0.2°C after ICE ingestion compared with 0.1 ± 0.1°C (P<0.001) with CON. During the run, the rate of rise in Tgi was greater (P=0.01) with ICE than with CON for the first 15 min. At the end of time-trial, Tgi was higher with ICE (40.2 ± 0.6°C) than CON (39.8 ± 0.4°C, P=0.005). Ratings of thermal sensation were lower during the cooling phase and for the first kilometre of the run ( - 1.2 ± 0.8; P<0.001). Although ingestion of ice slurry resulted in a transient increase in heat strain following a warm up routine, it is a practical and effective pre-competition cooling manoeuvre to improve performance in warm and humid environments.
2.
Thermotolerance and heat acclimation may share a common mechanism in humans.
Kuennen, M, Gillum, T, Dokladny, K, Bedrick, E, Schneider, S, Moseley, P
American journal of physiology. Regulatory, integrative and comparative physiology. 2011;(2):R524-33
Abstract
Thermotolerance and heat acclimation are key adaptation processes that have been hitherto viewed as separate phenomena. Here, we provide evidence that these processes may share a common basis, as both may potentially be governed by the heat shock response. We evaluated the effects of a heat shock response-inhibitor (quercetin; 2,000 mg/day) on established markers of thermotolerance [gastrointestinal barrier permeability, plasma TNF-α, IL-6, and IL-10 concentrations, and leukocyte heat shock protein 70 (HSP70) content]. Heat acclimation reduced body temperatures, heart rate, and physiological strain during exercise/heat stress) in male subjects (n = 8) completing a 7-day heat acclimation protocol. These same subjects completed an identical protocol under placebo supplementation (placebo). Gastrointestinal barrier permeability and TNF-α were increased on the 1st day of exercise/heat stress in quercetin; no differences in these variables were reported in placebo. Exercise HSP70 responses were increased, and plasma cytokines (IL-6, IL-10) were decreased on the 7th day of heat acclimation in placebo; with concomitant reductions in exercise body temperatures, heart rate, and physiological strain. In contrast, gastrointestinal barrier permeability remained elevated, HSP70 was not increased, and IL-6, IL-10, and exercise body temperatures were not reduced on the 7th day of heat acclimation in quercetin. While exercise heart rate and physiological strain were reduced in quercetin, this occurred later in exercise than with placebo. Consistent with the concept that thermotolerance and heat acclimation are related through the heat shock response, repeated exercise/heat stress increases cytoprotective HSP70 and reduces circulating cytokines, contributing to reductions in cellular and systemic markers of heat strain. Exercising under a heat shock response-inhibitor prevents both cellular and systemic heat adaptations.
3.
Influence of age on the thermic response to caffeine in women.
Arciero, PJ, Bougopoulos, CL, Nindl, BC, Benowitz, NL
Metabolism: clinical and experimental. 2000;(1):101-7
Abstract
The purpose of this study was to examine age-related differences in the magnitude of caffeine-induced thermogenesis and the relationship of aerobic fitness, body composition, and hormone and substrate concentrations to the thermic effect of caffeine in younger and older women. Using a placebo-controlled, double-blind study design, 10 older (50 to 67 years) and 10 younger (21 to 31 years) healthy women who were moderate consumers of caffeine (self-reported intake: younger, 139 +/- 152 mg/d; older, 204 +/- 101 mg/d, NS, mean +/- SD) were characterized for fasting plasma glucose, insulin, free fatty acid (FFA), and caffeine levels, energy expenditure, body composition, anthropometry, aerobic fitness, physical activity, and energy intake. Before and after placebo and caffeine ingestion (5 mg/kg fat-free mass [FFM]), the following variables were measured: fasting plasma glucose, insulin, FFA, and energy expenditure, plasma glucose, insulin, and FFA, and energy expenditure in response to placebo and caffeine ingestion. Caffeine ingestion resulted in similar increases in younger and older women for plasma caffeine (younger, 80 +/- 34 to 5,604 +/- 528 ng/mL, P < .01; older, 154 +/- 134 to 5,971 +/- 867 ng/mL, P < .01) and fatty acids (younger, 294 +/- 118 to 798 +/- 248 micromol/L, P < .01; older, 360 +/- 180 to 727 +/- 310 micromol/L, P < .01), whereas plasma insulin and glucose levels remained unchanged from baseline. Energy expenditure increased following caffeine ingestion in both groups (younger, 15.4%, 1.09 +/- 0.14 to 1.24 +/- 0.13 kcal/min, P < .05; older, 7.8%, 0.98 +/- 0.14 to 1.06 +/- 0.12 kcal/min, P < .05), although there was a blunted thermic response in the older versus younger women (older, 6.9 +/- 5 kcal/90 min; younger, 15.5 +/- 7 kcal/90 min, P < .05). In younger women, the thermic response to caffeine was positively correlated with the waist circumference (r = .70, P < .05) and body weight (r = .91; P < .01), whereas aerobic fitness (r = .77; P < .05) was the only significant correlate in older women. In conclusion, older and younger women increase energy expenditure significantly following caffeine ingestion, but older women have a blunted thermic response compared with younger women. Second, the thermic response to caffeine is positively associated with the body weight and waist circumference in younger women, whereas a positive association with aerobic fitness was observed in older women. Thus, the physiologic determinants of the thermic response to caffeine differ among women of different age groups.