Physiologia (Feb 2023)

Fluid Replacement Strategies and Heart Rate Variability Recovery Following Prolonged Exercise in the Heat and Mild Dehydration

  • Ciara N. Manning,
  • Margaret C. Morrissey,
  • Sean P. Langan,
  • Rebecca L. Stearns,
  • Robert A. Huggins,
  • Ryan M. Curtis,
  • Yasuki Sekiguchi,
  • Srinivas Laxminarayan,
  • Jaques Reifman,
  • Douglas J. Casa

DOI
https://doi.org/10.3390/physiologia3010008
Journal volume & issue
Vol. 3, no. 1
pp. 98 – 112

Abstract

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Background: In sporting and combat settings, optimal fluid replacement is rarely achieved, exacerbating physiological strain. It is unknown if prescribed fluid replacement following exercise in heat impacts heart rate variability (HRV). Purpose: Compare prescribed drinking (PD) and ad libitum (AL) fluid replacement on HRV following exercise in heat. Methods: Twelve participants (26 ± 5 years, VO2max: 58.44 ± 7.05 mL·kg−1·min−1) completed three trials in heat (36 °C, 36% humidity) on separate days, and were placed into groups, PD or AL. Recovery was assessed ~24 h later (hydration and HRV). HRV time and frequency was measured using a 3-lead electrocardiogram. Two-way repeated measures analysis of variance measured changes in HRV pre-trial, post-trial, and follow-up between groups. Data reported: p-value, mean difference (MD). Results: Fluid consumption was greater in PD during recovery (p = 0.012, MD = 1245 mL). Both groups were euhydrated at follow-up. HRV time (p p 2) decreased post-trial and increased by follow-up (time, p p 2). HRV was similar between groups (p > 0.05). Conclusions: Replacing ≥60% fluid sufficiently rehydrates and restores HRV 24 h post-exercise in heat and mild dehydration (BML ≤ 3%). Prescribed fluid consumption during recovery was ~30% greater. Additional measures of recovery sensitive to heat strain may provide a more holistic understanding of specific mechanisms of recovery.

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