Search

Introduction: Despite sparse systematic evidence, current exercise heat safety recommendations suggest that antihistamines blunt sweating and increase the risk for heat-related injury during exertional heat stress. The primary purpose of the present study was to examine whether diphenhydramine hydrochloride (DPH), a first-generation antihistamine, affects the sweating, core temperature, and heart rate (HR) response during exertional heat stress using a double-blind randomized crossover design., Methods: On two occasions separated by >48 h, 20 healthy adults (10 females, 23 ± 3 yr, body surface area: 1.9 ± 0.2 m 2 , body mass index: 23.7 ± 2.2 kg·m -2 ) orally consumed either 50 mg of DPH or placebo (PLA), and then rested for 2 h in a climate-controlled room maintained at 30°C and 35% relative humidity (heat index of ~29°C), followed by a 60-min fixed-heat production treadmill walk (6.3 ± 1.0 W·kg -1 ). Whole-body sweat loss, local sweat rate, rectal temperature ( Trec ), and HR were measured., Results: Whole-body sweat loss was not different between conditions (PLA: 406 ± 78 g, DPH: 396 ± 75 g; P = 0.26, treatment effect: -10 g; 95% confidence interval, -28 to 8). No differences were observed for the onset of sweating (PLA: 13.5 ± 2.4 min, DPH: 13.3 ± 2.7 min; P = 0.79) and steady-state local sweat rate (PLA: 0.83 ± 0.26 mg·cm -2 ·min -1 , DPH: 0.82 ± 0.27 mg·cm -2 ·min -1 ; P = 0.99). No difference in baseline Trec was observed (PLA: 37.09°C ± 0.35°C, DPH: 37.13°C ± 0.33°C; P = 0.68), and the 60-min Δ Trec was not different ( P = 0.99) between PLA (0.83°C ± 0.29°C) and DPH (0.81°C ± 0.30°C). HR was similar at baseline (PLA: 86 ± 13 bpm, DPH: 84 ± 11 bpm; P = 0.30) and end-exercise (PLA: 134 ± 28 bpm, DPH: 132 ± 26 bpm; P = 0.90)., Conclusions: Fifty milligrams of DPH does not modify the sweating, core temperature, and HR response during exertional heat stress in young healthy adults., (Copyright © 2024 by the American College of Sports Medicine.)

The present study assessed agreement between a wireless sweat rate monitor (KuduSmart® device) and the ventilated capsule (VC) technique for measuring: (i) minute-averaged local sweat rate (LSR), (ii) sweating onset, (iii) sudomotor thermosensitivity, and (iv) steady-state LSR, during passive heat stress and exercise. It was hypothesized that acceptable agreement with no bias would be observed between techniques for all assessed sweating characteristics. On two separate occasions for each intervention, participants were either passively heated by recirculating hot water (49 °C) through a tube-lined garment until rectal temperature increased 1 °C over baseline ( n  = 8), or a 60 min treadmill march at a fixed rate of heat production (∼500 W, n  = 9). LSR of the forearm was concurrently measured with a VC and the KuduSmart® device secured within ∼2 cm. Using a ratio scale Bland-Altman analysis with the VC as the reference, the KuduSmart® device demonstrated systematic bias and not acceptable agreement for minute-averaged LSR (1.17 [1.09, 1.27], CV = 44.5%), systematic bias and acceptable agreement for steady-state LSR (1.16 [1.09,1.23], CV = 19.5%), no bias and acceptable agreement for thermosensitivity (1.07 [0.99, 1.16], CV = 23.2%), and no bias and good agreement for sweating onset (1.00 [1.00, 1.00], CV = 11.1%). In total, ≥73% of all minute-averaged LSR observations with the KuduSmart ® device ( n  = 2743) were within an absolute error of <0.2 mg/cm 2 /min to the VC, the reference minimum detectable change in measurement error of a VC on the forearm. Collectively, the KuduSmart ® device may be a satisfactory solution for assessing the sweating response to heat stress where a VC is impractical., Competing Interests: The KuduSmart® device was provided at no cost to Dr. Nicholas Ravanelli from Crossbridge Scientific Ltd. Crossbridge Scientific Ltd was not involved in study design, data collection, analysis, interpretation of results, or manuscript preparation.