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Exercise Heart Rate Variability Suggests Parasympathetic Hyperactivity during Simulated Military Operations Irrespective of Testosterone Administration.

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Title: Exercise Heart Rate Variability Suggests Parasympathetic Hyperactivity during Simulated Military Operations Irrespective of Testosterone Administration.
Authors: LOWE, ADAM C.1, NICLOU, ALEXANDRA1,2,3 alexandra.m.niclou.ctr@health.mil, VARANOSKE, ALYSSA N.4 alyssa.n.varanoske@nasa.gov, HARRIS, MELISSA N.1 melissa.harris@pbrc.edu, HEBERT, CALLIE1 Callie.Hebert@pbrc.edu, JOHANNSEN, NEIL M.1 neil.johannsen@pbrc.edu, HEYMSFIELD, STEVEN B.1 Steven.Heymsfield@pbrc.edu, GREENWAY, FRANK L.1 frank.Greenway@pbrc.edu, MARGOLIS, LEE M.2 lee.m.margolis.civ@health.mil, LIEBERMAN, HARRIS R.2 harris.r.lieberman.civ@health.mil, BEYL, ROBBIE A.1 robbie.beyl@pbrc.edu, FERRANDO, ARNY A.5 AFerrando@uams.edu, PASIAKOS, STEFAN M.2,6 stefan.pasiakos@nih.gov, ROOD, JENNIFER C.1 jennifer.rood@pbrc.edu
Source: Medicine & Science in Sports & Exercise. Sep2025, Vol. 57 Issue 9, p1979-1987. 9p.
Subject Terms: *Academic medical centers, *Comparative studies, Autonomic nervous system physiology, Testosterone, Heart rate monitoring, Placebos, T-test (Statistics), Research funding, High-intensity interval training, Statistical sampling, Randomized controlled trials, Descriptive statistics, Chi-squared test, Injections, Heart beat, Military service, Data analysis software, Regression analysis
Geographic Terms: United States
Abstract: Introduction: Heart rate variability (HRV), typically measured at rest, is a measure of autonomic balance sensitive to physical and psychological stress. Testosterone supplementation during multistressor military operations may maintain exercise HRV by preventing a decrease in cardiac autonomic tone. The purpose of this study was to assess exercise HRV as a marker of physiological and psychological stress and determine if testosterone administration maintains HRV during extended simulated military operations. Methods: Thirty-two physically active males were enrolled in this parallel arm, randomized, placebo-controlled, double-blind study. Participants were randomized to receive a single injection of testosterone undecanoate (TEST, n = 16) or an isovolumetric placebo (PLA, n = 16) and completed 20 d of simulated operations cycles comprised of low-stress and high-stress days. Simulated operations were comprised of 4 cycles of two low-stress days (LS, ~1000 kcal of exercise-induced energy expenditure [EIEE] and 8 h of sleep) and three high-stress days (HS, ~3000 kcal EIEE, 4 h of sleep). Heart rate was collected during daily load carriage (~30% of body weight) exercise between 0500 and 0800 h. Short-term exercise HRV during this load carriage exercise was assessed through standard deviation of normal-to-normal beats (SDNN), root-mean-square of successive differences (RMSSD) between normal heart beats, low-frequency (LF) and high-frequency (HF) heartbeat sequences, and the ratio of LF to HF (LF/HF). Results: SDNN and RMSSD increased from the first to the last LS day (P = 0.018 and P = 0.003, respectively) and from the first to the last HS day (P = 0.006 and P < 0.001, respectively). LF and HF also increased from the first to the last LS day (P = 0.027 and P = 0.028, respectively) and from the first to the last HS day (P = 0.004 and P = 0.002, respectively), whereas LF/HF was unchanged across these time points (P = 0.800 and P = 0.643, respectively). TEST showed higher LF/HF ratio on LS days (P = 0.006) and HS days (P < 0.001) compared with PLA. Conclusions: Exercise HRV metrics suggested parasympathetic hyperactivity despite concomitant increases in stress across the extended simulated military operations. A single dose of TEST does not appear to negatively affect the autonomic response to high stress in young health physically active males. [ABSTRACT FROM AUTHOR]
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Database: Education Research Complete
Description
Abstract:Introduction: Heart rate variability (HRV), typically measured at rest, is a measure of autonomic balance sensitive to physical and psychological stress. Testosterone supplementation during multistressor military operations may maintain exercise HRV by preventing a decrease in cardiac autonomic tone. The purpose of this study was to assess exercise HRV as a marker of physiological and psychological stress and determine if testosterone administration maintains HRV during extended simulated military operations. Methods: Thirty-two physically active males were enrolled in this parallel arm, randomized, placebo-controlled, double-blind study. Participants were randomized to receive a single injection of testosterone undecanoate (TEST, n = 16) or an isovolumetric placebo (PLA, n = 16) and completed 20 d of simulated operations cycles comprised of low-stress and high-stress days. Simulated operations were comprised of 4 cycles of two low-stress days (LS, ~1000 kcal of exercise-induced energy expenditure [EIEE] and 8 h of sleep) and three high-stress days (HS, ~3000 kcal EIEE, 4 h of sleep). Heart rate was collected during daily load carriage (~30% of body weight) exercise between 0500 and 0800 h. Short-term exercise HRV during this load carriage exercise was assessed through standard deviation of normal-to-normal beats (SDNN), root-mean-square of successive differences (RMSSD) between normal heart beats, low-frequency (LF) and high-frequency (HF) heartbeat sequences, and the ratio of LF to HF (LF/HF). Results: SDNN and RMSSD increased from the first to the last LS day (P = 0.018 and P = 0.003, respectively) and from the first to the last HS day (P = 0.006 and P < 0.001, respectively). LF and HF also increased from the first to the last LS day (P = 0.027 and P = 0.028, respectively) and from the first to the last HS day (P = 0.004 and P = 0.002, respectively), whereas LF/HF was unchanged across these time points (P = 0.800 and P = 0.643, respectively). TEST showed higher LF/HF ratio on LS days (P = 0.006) and HS days (P < 0.001) compared with PLA. Conclusions: Exercise HRV metrics suggested parasympathetic hyperactivity despite concomitant increases in stress across the extended simulated military operations. A single dose of TEST does not appear to negatively affect the autonomic response to high stress in young health physically active males. [ABSTRACT FROM AUTHOR]
ISSN:01959131
DOI:10.1249/MSS.0000000000003743