Communicated by Narihiko Kondo.
The online version of this article (https://doi.org/10.1007/s00421-017-3758-y) contains supplementary material, which is available to authorized users.
Heat adaptation (HA) is critical to performance and health in a hot environment. Transition from short-term heat acclimatisation (STHA) to long-term heat acclimatisation (LTHA) is characterised by decreased autonomic disturbance and increased protection from thermal injury. A standard heat tolerance test (HTT) is recommended for validating exercise performance status, but any role in distinguishing STHA from LTHA is unreported. The aims of this study were to (1) define performance status by serial HTT during structured natural HA, (2) evaluate surrogate markers of autonomic activation, including heart rate variability (HRV), in relation to HA status.
Participants (n = 13) were assessed by HTT (60-min block-stepping, 50% VO2peak) during STHA (Day 2, 6 and 9) and LTHA (Day 23). Core temperature (Tc) and heart rate (HR) were measured every 5 min. Sampling for HRV indices (RMSSD, LF:HF) and sympathoadrenal blood measures (cortisol, nephrines) was undertaken before and after (POST) each HTT.
Significant (P < 0.05) interactions existed for Tc, logLF:HF, cortisol and nephrines (two-way ANOVA; HTT by Day). Relative to LTHA, POST results differed significantly for Tc (Day 2, 6 and 9), HR (Day 2), logRMSSD (Day 2 and Day 6), logLF:HF (Day 2 and Day 6), cortisol (Day 2) and nephrines (Day 2 and Day 9). POST differences in HRV (Day 6 vs. 23) were + 9.9% (logRMSSD) and − 18.6% (logLF:HF).
Early reductions in HR and cortisol characterised STHA, whereas LTHA showed diminished excitability by Tc, HRV and nephrine measures. Measurement of HRV may have potential to aid real-time assessment of readiness for activity in the heat.
Supplemental Material 1. (DOCX 16 KB)421_2017_3758_MOESM1_ESM.docx
Adolph EF (1947) Physiology of man in the desert. Interscience Publishers Inc., New York
Borg G (1970) Perceived exertion as an indicator of somatic stress. Scand J Rehabil Med 2:92–98 PubMed
Carrillo AE, Cheung SS, Flouris AD (2013) Autonomic nervous system modulation during accidental syncope induced by heat and orthostatic stress. Aviat Sp Environ Med 84:722–725 CrossRef
Deutschbein T, Unger N, Jaeger A, Broecker-Preuss M, Mann K, Petersenn S (2010) Influence of various confounding variables and storage conditions on metanephrine and normetanephrine levels in plasma. Clin Endocrinol (Oxf) 73:153–160
Harris EK, Yasaka T (1983) On the calculation of a “reference change” for comparing two consecutive measurements. Clin Chem 29:25–30 PubMed
Hodge D, Jones D, Martinez R, Buono MJ (2013) Time course of the attenuation of sympathetic nervous activity during active heat acclimation. Auton Neurosci Basic Clin 177:101–103 CrossRef
Horowitz M (2016) Epigenetics and cytoprotection with heat acclimation. J Appl Physiol (1985) 120:702–710 CrossRef
Iellamo F (2001) Neural mechanisms of cardiovascular regulation during exercise. Auton Neurosci Basic Clin 90:66–75 CrossRef
Maher JT, Bass DE, Heistad DD, Angelakos ET, Hartley LH (1972) Effect of posture on heat acclimation in man. J Appl Physiol (1985) 33:8–13 CrossRef
Roden M, Raffesberg W, Raber W, Bernroider E, Niederle B, Waldhausl W et al (2001) Quantification of unconjugated metanephrines in human plasma without interference by acetaminophen. Clin Chem 47:1061–1067 PubMed
Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology (1996) Heart rate variability: standards of measurement, physiological interpretation and clinical use. Circulation 93:1043–1065 CrossRef
Wilkinson DM, Carter JM, Richmond VL, Blacker SD, Rayson MP (2008) The effect of cool water ingestion on gastrointestinal pill temperature. Med Sci Sports Exerc 2008 40(3):523–528 CrossRef
Woods DR, O’Hara JP, Boos CJ, Hodkinson PD, Tsakirides, Hill NE, Jose D, Hawkins A, Phillipson K, Hazlerigg A, Arjomandkhah N, Gallagher L, Holdsworth D, Cooke M, Green ND, Mellor A (2017) Markers of physiological stress during exercise under conditions of normoxia, normobaric hypoxia, hypobaric hypoxia, and genuine high altitude. Eur J Appl Physiol 117:893–900 CrossRefPubMedPubMedCentral
- Heart rate variability and plasma nephrines in the evaluation of heat acclimatisation status
Major Michael John Stacey
S. K. Delves
D. R. Woods
S. E. Britland
A. J. Allsopp
S. J. Brett
J. L. Fallowfield
C. J. Boos
- Springer Berlin Heidelberg