The influence of a hot environment on physiological stress responses in exercise until exhaustion

Exhaustive exercise in a hot environment can impair performance. Higher epinephrine plasma levels occur during exercise in heat, indicating greater sympathetic activity. This study examined the influence of exercise in the heat on stress levels. Nine young healthy men performed a maximal progressive test on a cycle ergometer at two different environmental conditions: hot (40 degrees C) and normal (22 degrees C), both between 40% and 50% relative humidity. Venous blood and saliva samples were collected pre-test and post-test. Before exercise there were no significant changes in salivary biomarkers (salivary IgA: p = 0.12; alpha-amylase: p = 0.66; cortisol: p = 0.95; nitric oxide: p = 0.13; total proteins: p = 0.07) or blood lactate (p = 0.14) between the two thermal environments. Following exercise, there were significant increases in all variables (salivary IgA 22 degrees C: p = 0.04, 40 degrees C: p = 0.0002; alpha-amylase 22 degrees C: p = 0.0002, 40 degrees C: p = 0.0002; cortisol 22 degrees C: p = 0.02, 40 degrees C: p = 0.0002; nitric oxide 22 degrees C: p = 0.0005, 40 degrees C: p = 0.0003, total proteins 22 degrees C: p<0.0001, 40 degrees C: p<0.0001 and; blood lactate 22 degrees C: p<0.0001, 40 degrees C: p<0.0001) both at 22 degrees C and 40 degrees C. There was no significant adjustment regarding IgA levels between the two thermal environments (p = 0.74), however the levels of alpha-amylase (p = 0.02), cortisol (p<0.0001), nitric oxide (p = 0.02) and total proteins (p = 0.01) in saliva were higher in the hotter conditions. Blood lactate was lower under the hot environment (p = 0.01). In conclusion, enduring hot temperature intensified stressful responses elicited by exercise. This study advocates that hot temperature deteriorates exercise performance under exhaustive stress and effort conditions

Parental childhood growth and offspring birthweight : Pooled analyses from four birth cohorts in low and middle income countries

Funding Information Bill and Melinda Gates Foundation. Grant Number: OPP1020058 Wellcome Trust 089257/Z/09/Z Contract grant sponsor: the National Heart, Lung and Blood Institute at National Institutes of Health. Grant Number: HHSN 268200900028C to the Center of Excellence – INCAP/ Guatemala; and Grand Challenges Canada (Grant number: 0072‐03 to the Grantee, The Trustees of the University of Pennsylvania)Peer reviewedPublisher PD