European Journal of Applied Physiology

, Volume 114, Issue 4, pp 785–792 | Cite as

Heart rate variability during exertional heat stress: effects of heat production and treatment

  • Andreas D. Flouris
  • Andrea Bravi
  • Heather E. Wright-Beatty
  • Geoffrey Green
  • Andrew J. Seely
  • Glen P. KennyEmail author
Original Article



We assessed the efficacy of different treatments (i.e., treatment with ice water immersion vs. natural recovery) and the effect of exercise intensities (i.e., low vs. high) for restoring heart rate variability (HRV) indices during recovery from exertional heat stress (EHS).


Nine healthy adults (26 ± 3 years, 174.2 ± 3.8 cm, 74.6 ± 4.3 kg, 17.9 ± 2.8 % body fat, 57 ± 2 mL·kg·−1 min−1 peak oxygen uptake) completed four EHS sessions incorporating either walking (4.0–4.5 km·h−1, 2 % incline) or jogging (~7.0 km·h−1, 2 % incline) on a treadmill in a hot-dry environment (40 °C, 20–30 % relative humidity) while wearing a non-permeable rain poncho for a slow or fast rate of rectal temperature (T re) increase, respectively. Upon reaching a T re of 39.5 °C, participants recovered until T re returned to 38 °C either passively or with whole-body immersion in 2 °C water. A comprehensive panel of 93 HRV measures were computed from the time, frequency, time–frequency, scale-invariant, entropy and non-linear domains.


Exertional heat stress significantly affected 60/93 HRV measures analysed. Analyses during recovery demonstrated that there were no significant differences between HRV measures that had been influenced by EHS at the end of passive recovery vs. whole-body cooling treatment (p > 0.05). Nevertheless, the cooling treatment required statistically significantly less time to reduce T re (p < 0.001).


While EHS has a marked effect on autonomic nervous system modulation and whole-body immersion in 2 °C water results in faster cooling, there were no observed differences in restoration of autonomic heart rate modulation as measured by HRV indices with whole-body cold-water immersion compared to passive recovery in thermoneutral conditions.


Exercise-induced hyperthermia EHS Heart rate variability HRV Core temperature Hyperthermia 



Autonomic nervous system




Exertional heat stress

FH + C

Fast heating with whole-body cooling session

FH + N

Fast heating with natural recovery session


Heart rate variability


Normal-to-normal heart rate variability


Root mean square of differences of successive normal-to-normal intervals

R–R interval

Time between two consecutive R waves in the electrocardiogram

SH + C

Slow heating with whole-body cooling session

SH + N

Slow heating with natural recovery session


Rectal temperature

\( \dot{V}{\text{O}}_{{ 2 {\text{peak}}}} \)

Peak oxygen consumption



This research was supported by the Natural Sciences and Engineering Research Council (RGPIN-298159-2009) and Canada Foundation for Innovation—Leaders Opportunity Fund (22529); (grants held by Dr. Glen Kenny). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The authors wish to thank the lab members of the Human and Environmental Physiology Research Unit for their assistance during data collection and the time and effort of all the participants.

Conflict of interest

Andrew J. E. Seely is the founder and Chief Science Officer, and Geoffrey Green is the Product Manager of Therapeutic Monitoring Systems (TMS). TMS aims to commercialize patented continuous individualized multi-organ variability analysis (CIMVA) technology, with the objective of delivering variability-directed clinical decision support to improve quality and efficiency of care. All the other authors have no conflicts of interest to disclose.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Andreas D. Flouris
    • 1
  • Andrea Bravi
    • 2
  • Heather E. Wright-Beatty
    • 3
  • Geoffrey Green
    • 2
  • Andrew J. Seely
    • 2
  • Glen P. Kenny
    • 3
    Email author
  1. 1.FAME LaboratoryCentre for Research and Technology HellasTrikalaGreece
  2. 2.Divisions of Thoracic Surgery and Critical Care MedicineOttawa Hospital-General Campus, Ottawa Health Research InstituteOntarioCanada
  3. 3.Human and Environmental Physiology Research Unit, Faculty of Health Sciences, School of Human KineticsUniversity of OttawaOttawaCanada

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