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Original research
Gait instability and estimated core temperature predict exertional heat stroke
  1. Mark Buller1,
  2. Rebecca Fellin1,
  3. Max Bursey2,
  4. Meghan Galer3,
  5. Emma Atkinson1,
  6. Beth A Beidleman1,
  7. Michael J Marcello1,
  8. Kyla Driver1,
  9. Timothy Mesite1,
  10. Joseph Seay1,4,
  11. Lara Weed5,
  12. Brian Telfer5,
  13. Christopher King4,
  14. Royce Frazee6,
  15. Charles Moore6,
  16. James R Williamson5
  1. 1United States Army Research Institute of Environmental Medicine, Natick, Massachusetts, USA
  2. 2Augusta University, Augusta, Georgia, USA
  3. 3Martin Army Community Hospital, Fort Benning, Georgia, USA
  4. 4Natick Soldier Systems Center, Natick, Massachusetts, USA
  5. 5Massachusetts Institute of Technology Lincoln Laboratory, Lexington, Massachusetts, USA
  6. 675th Ranger Regiment, Fort Benning, Georgia, USA
  1. Correspondence to Dr Mark Buller, United States Army Research Institute of Environmental Medicine, Natick, MA 01516, USA; mark.j.buller.civ{at}mail.mil

Abstract

Objective Exertional heat stroke (EHS), characterised by a high core body temperature (Tcr) and central nervous system (CNS) dysfunction, is a concern for athletes, workers and military personnel who must train and perform in hot environments. The objective of this study was to determine whether algorithms that estimate Tcr from heart rate and gait instability from a trunk-worn sensor system can forward predict EHS onset.

Methods Heart rate and three-axis accelerometry data were collected from chest-worn sensors from 1806 US military personnel participating in timed 4/5-mile runs, and loaded marches of 7 and 12 miles; in total, 3422 high EHS-risk training datasets were available for analysis. Six soldiers were diagnosed with heat stroke and all had rectal temperatures of >41°C when first measured and were exhibiting CNS dysfunction. Estimated core temperature (ECTemp) was computed from sequential measures of heart rate. Gait instability was computed from three-axis accelerometry using features of pattern dispersion and autocorrelation.

Results The six soldiers who experienced heat stroke were among the hottest compared with the other soldiers in the respective training events with ECTemps ranging from 39.2°C to 40.8°C. Combining ECTemp and gait instability measures successfully identified all six EHS casualties at least 3.5 min in advance of collapse while falsely identifying 6.1% (209 total false positives) examples where exertional heat illness symptoms were neither observed nor reported. No false-negative cases were noted.

Conclusion The combination of two algorithms that estimate Tcr and ataxic gate appears promising for real-time alerting of impending EHS.

  • hot temperature
  • heat-shock response
  • physical activity
  • preventive medicine

Data availability statement

No data are available. Data are not publicly available.

https://doi.org/10.1136/bjsports-2021-104081

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    Data availability statement

    No data are available. Data are not publicly available.

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    Footnotes

    • Contributors Study conception and design: MBul, RF, JS, MG and MBur; significant data acquisition: MBul, MBur, MG, BAB, MJM, KD, TM, CK, RF and CM; significant data analysis: MBul, EA, MJM, KD, TM, LW, BT and JRW; significant writing: MBul, RF, EA and JRW; critical review and revision input: all listed authors.

    • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

    • Disclaimer The views expressed in this paper are those of the authors and do not reflect the official policy of the Department of Army or Department of Defence (DoD). The MIT Lincoln Laboratory contribution to this work was supported by the Department of the Army under Air Force Contract No. FA8702-15-D-0001.

    • Competing interests MBul is the listed inventor on a patent for estimating core body temperature from heart rate, also known as estimated core temperature (ECTemp). Ownership of the ECTemp patent is held by the US Department of the Army. MBul, RF, JS, BT and JRW and LW are the listed inventors on a patent application, 'System and Method to Predict Exertional Heat Stroke from Torso-Worn Sensor'. This patent is jointly owned by the US Department of the Army and Massachusetts Institute of Technology, Lincoln Laboratory. As part of the Department of Defense employee incentive programmes, MBul, RF and JS are entitled to receive a portion of royalty payments for any licensing of the algorithms.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.