In:
Medicine & Science in Sports & Exercise, Ovid Technologies (Wolters Kluwer Health), Vol. 56, No. 4 ( 2024-4), p. 644-654
Abstract:
Heat adaptation is protective against heat illness; however, its role in heat syncope, due to reflex mechanisms, has not been conclusively established. The aim of this study was to evaluate if heat acclimation (HA) was protective against heat syncope and to ascertain underlying physiological mechanisms. Methods Twenty (15 males, 5 females) endurance-trained athletes were randomized to either 8 d of mixed active and passive HA (HEAT) or climatically temperate exercise (CONTROL). Before, and after, the interventions participants underwent a head up tilt (HUT) with graded lower body negative pressure (LBNP), in a thermal chamber (32.0 ± 0.3°C), continued until presyncope with measurement of cardiovascular parameters. Heat stress tests (HST) were performed to determine physiological and perceptual measures of HA. Results There was a significant increase in orthostatic tolerance (OT), as measured by HUT/LBNP, in the HEAT group (preintervention; 28 ± 9 min, postintervention; 40 ± 7 min) compared with CONTROL (preintervention; 30 ± 8 mins, postintervention; 33 ± 5 min) ( P = 0.01). Heat acclimation resulted in a significantly reduced peak and mean rectal and skin temperature ( P 〈 0.01), peak heat rate ( P 〈 0.003), thermal comfort ( P 〈 0.04), and rating of perceived exertion ( P 〈 0.02) during HST. There was a significantly increased plasma volume (PV) in the HEAT group in comparison to CONTROL ( P = 0.03). Conclusions Heat acclimation causes improvements in OT and is likely to be beneficial in patients with heat exacerbated reflex syncope. Heat acclimation–mediated PV expansion is a potential physiological mechanism underlying improved OT.
Type of Medium:
Online Resource
ISSN:
1530-0315
,
0195-9131
DOI:
10.1249/MSS.0000000000003355
Language:
English
Publisher:
Ovid Technologies (Wolters Kluwer Health)
Publication Date:
2024
detail.hit.zdb_id:
2031167-9
SSG:
31
Permalink
