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Fluid loss during exercise-heat stress reduces cardiac vagal autonomic modulation


Macartney, MJ and Meade, RD and Notley, SR and Herry, CL and Seely, AJE and Kenny, GP, Fluid loss during exercise-heat stress reduces cardiac vagal autonomic modulation, Medicine and Science in Sports and Exercise, 52, (2) pp. 362-369. ISSN 0195-9131 (2020) [Refereed Article]

Copyright Statement

Copyright 2019 by the American College of Sports Medicine

DOI: doi:10.1249/MSS.0000000000002136


Purpose: Sweat-induced fluid loss during prolonged exercise-heat stress can compromise cardiovascular and thermoregulatory function, although its effects on cardiac autonomic modulation remain unclear. We therefore examined heart rate variability (HRV) and recovery (HRRec), as surrogates of cardiac autonomic modulation, during and after prolonged exercise in the heat with and without fluid replacement.

Methods: Eleven young and healthy men performed 90 min of semi-recumbent cycling in dry heat (40C; 20% relative humidity) at a fixed rate of metabolic heat production (600 W; ~46% V˙O2peak) followed by 40-min resting recovery without fluid replacement (No-FR; ~3.4% reduction in body mass). On a separate day, participants completed the same protocol with fluid replacement (FR; 500-700 mL timed boluses) to offset sweat losses. Esophageal temperature and ECG were recorded throughout, with measurements analyzed over 10-min averaged epochs during baseline, each 30-min interval during exercise and 20-min interval during recovery.

Results: Esophageal temperature and heart rate were elevated in No-FR relative to FR throughout exercise (all P ≤ 0.02). The HRV indices reflecting vagal influence of heart rate including the cardiac vagal index (CVI = log10[16 SD1 SD2]) and root-mean-square of successive differences were attenuated throughout exercise relative to baseline in both conditions (all P < 0.05), with the magnitude of the reduction greater in the No-FR condition (all P < 0.05). Further, sample entropy was reduced throughout all time points measured during exercise in the No-FR relative to FR condition (all P ≤ 0.03).

Conclusions: Our unique observations indicate that while prolonged exercise heat stress attenuates the vagal influence and complexity of cardiac rhythms, that reduction is further exacerbated by fluid loss, highlighting the importance of fluid replacement in such conditions.

Item Details

Item Type:Refereed Article
Research Division:Health Sciences
Research Group:Sports science and exercise
Research Field:Exercise physiology
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the health sciences
UTAS Author:Macartney, MJ (Mr Michael Macartney)
ID Code:140061
Year Published:2020
Web of Science® Times Cited:7
Deposited By:Health Sciences
Deposited On:2020-07-23
Last Modified:2021-09-22

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