Impact of sodium citrate ingestion during recovery after strenuous exercise in the heat on heart rate variability: A randomized, crossover study

Abstract

Changes in hydration status influence plasma volume (PV) which is associated with post-exercise parasympathetic reactivation. The present study hypothesized that, after dehydrating cycling exercise in the heat (DE), stimulation of PV expansion with sodium citrate (CIT) supplementation would promote heart rate variability (HRV) recovery in endurance-trained men. Twelve participants lost 4% of body mass during DE. During subsequent 16-h recovery, participants consumed water ad libitum (CIT =5.5-L, PLC =5.1-L) and ate prescribed food supplemented with CIT or placebo in a randomized, double-blind, crossover manner. Relative changes in PV were assessed across DE and 16-h recovery. HRV was analyzed before and 16 h after DE in three conditions for altogether four 5-min periods: supine in a thermoneutral environment, supine in the heat (32°C, 46% relative humidity; 2 periods), and standing in the heat. A larger expansion of PV across 16-h recovery occurred in CIT compared to placebo trial (p < 0.0001). However, no between-trial differences appeared in HRV parameters (lnRMSSD, lnSDNN, lnLF/HF) in any 5-min period analyzed before or 16 h after DE (in all cases p > 0.05). Increases in HR (p < 0.001) and lnLF/HF (p = 0.005) and decreases in lnRMSSD (p < 0.001) and lnSDNN (p < 0.001) occurred following DE in both trials. Larger PV expansion induced by CIT supplementation after DE does not improve recovery of HRV at rest and has no influence on HRV responsiveness in endurance-trained men.

Keywords: dehydration; endurance athlete; exercise-heat stress; plasma volume.

FIGURE 1

CONSORT flow diagram for crossover‐studies. Displayed is the randomized allocation to the groups placebo (PLC) and sodium citrate (CIT)

FIGURE 2

Conditions of HR recording and recorded HR time periods used for HRV analysis. HR was recorded under three conditions (I, II, III) and four recorded HR time periods (Su‐Rt, Su‐H1, Su‐H2, St‐H3) were selected for HRV analysis. These procedures were carried out before (a) and after (c) dehydrating exercise in the heat that was followed by a 16‐h recovery under normal environmental conditions (b)

FIGURE 3

Plasma volume changes for the placebo and the citrate trials. Displayed is the plasma volume change relative to preDE (before dehydrating exercise) of 12 subjects (y‐axis) during dehydrating exercise in the heat (DE; x‐axis) and subsequent 16‐h recovery period (Recovery; x‐axis). Asterix marks a significant between‐trial difference (p < 0.05)

FIGURE 4

Interaction effect of measurement*trial*time period for the parameter heartrate. Displayed is the mean heartrate (y‐axis) of 12 subjects during 4 time periods (x‐axis) before dehydration exercise in the heat (preDE) and following 16‐h recovery after dehydrating exercise in the heat (postDE) with (a) sodium citrate (CIT) or (b) placebo (PLC) supplementation during recovery. Su‐Rt, supine position at room temperature; Su‐H1, supine position, after 10 min in the heat; Su‐H2, supine position, after 25 min in the heat; St‐H3, standing position, 5‐min periods of HR recordings selected for HRV analysis