AUTHOR=de Korte Johannus Q. , Veenstra Bertil J. , van Rijswick Mark , Derksen Eline J. K. , Hopman Maria T. E. , Bongers Coen C. W. G. , Eijsvogels Thijs M. H. 

TITLE=A Heart Rate Based Algorithm to Estimate Core Temperature Responses in Elite Athletes Exercising in the Heat

JOURNAL=Frontiers in Sports and Active Living

VOLUME=4

YEAR=2022

URL=https://www.frontiersin.org/journals/sports-and-active-living/articles/10.3389/fspor.2022.882254

DOI=10.3389/fspor.2022.882254

ISSN=2624-9367

ABSTRACT=<sec><title>Purpose</title><p>Non-invasive non-obtrusive continuous and real-time monitoring of core temperature (T<sub>c</sub>) may enhance pacing strategies, the efficacy of heat mitigation measures, and early identification of athletes at risk for heat-related disorders. The Estimated Core Temperature (ECTemp™) algorithm uses sequential heart rate (HR) values to predict T<sub>c</sub>. We examined the validity of ECTemp™ among elite athletes exercising in the heat.</p></sec><sec><title>Methods</title><p>101 elite athletes performed an exercise test in simulated hot and humid environmental conditions (ambient temperature: 31.6 ± 1.0°C, relative humidity: 74 ± 5%). T<sub>c</sub> was continuously measured using a validated ingestible telemetric temperature capsule system. In addition, HR was continuously measured and used to compute the estimated core temperature (T<sub>c−est</sub>) using the ECTemp™ algorithm.</p></sec><sec><title>Results</title><p>Athletes exercised for 44 ± 10 min and <italic>n</italic> = 5,025 readouts of T<sub>c</sub> (range: 35.8–40.4°C), HR (range: 45–207 bpm), and T<sub>c−est</sub> (range: 36.7–39.9°C) were collected. T<sub>c−est</sub> demonstrated a small yet significant bias of 0.15 ± 0.29°C (<italic>p</italic> &lt; 0.001) compared to T<sub>c</sub>, with a limit of agreement of ±0.45°C and a root mean square error of 0.35 ± 0.18°C. Utilizing the ECTemp™ algorithm as a diagnostic test resulted in a fair to excellent sensitivity (73–96%) and specificity (72–93%) for T<sub>c−est</sub> thresholds between 37.75 and 38.75°C, but a low to very-low sensitivity (50–0%) for T<sub>c−est</sub> thresholds &gt;39.0°C, due to a high prevalence of false-negative observations.</p></sec><sec><title>Conclusion</title><p>ECTemp™ provides a valuable and representative indication of thermal strain in the low- to mid-range of T<sub>c</sub> values observed during exercise in the heat. It may, therefore, be a useful non-invasive and non-obtrusive tool to inform athletes and coaches about the estimated core temperature during controlled hyperthermia heat acclimation protocols. However, the ECTemp™ algorithm, in its current form, should not solely be used to identify athletes at risk for heat-related disorders due to low sensitivity and high false-negative rate in the upper end of the T<sub>c</sub> spectrum.</p></sec>