Gait instability and estimated core temperature predict exertional heat stroke

Wearable and ingestible technology to evaluate and prevent exertional heat illness: A narrative review

Exertional heat illness remains a constant threat to the athlete, military service member, and laborer. Recent increases in the number and intensity of environmental heat waves places these populations at an ever increasing risk and can be deadly if not recognized and treated rapidly. For this reason, it is extremely important for medical providers to guide athletes, service members, and laborers in the implementation of awareness, education, and measures to reduce or mitigate the risk of exertional heat illness. Within the past 2 decades, a variety of wearable technology options have become commercially available to track an estimation of core temperature, yet questions continue to emerge as to its use, effectiveness, and practicality in athletics, the military, and the workforce. There is a paucity of data on the accuracy of many of these newer devices in the setting of true heat stroke physiology, and it is important to avoid overreliance on new wearable technology. Further research and improvement of this technology are critical to identify accuracy in the diagnosis and prevention of EHI.

Heat stroke burden and validity of wearable-derived core temperature estimation during elite military training

OBJECTIVES

Exertional heat stroke (EHS) remains a significant health concern while training in hot environments, prompting the development of noninvasive wearable technology for monitoring estimated core temperature (ECT). The objective of this study was to review the effectiveness of an ECT device during elite military training by providing a case series of individuals who developed EHS.

METHODS

This is a retrospective study of EHS cases during high-intensity training while wearing the ECT device, Zephyr BioharnessTM. Data was collected from January 2021 through September 2021 at the Air Force Special Warfare Training pipeline in San Antonio, TX. Rectal temperatures of EHS diagnoses, defined by central nervous system (CNS) dysfunction and rectal temperature approaching or >40°C (104°F), were compared to ECT reading via Zephyr BioharnessTM. Incidence rates and psychometric properties were calculated using R package.

RESULTS

A total of 47,058 daily peak ECT measurements were collected among 1,364 trainees. A total of 499 trainees flagged as potential EHS by Zephyr BioharnessTM reading >39.7°C (103.5°F). The incidence of confirmed EHS was 0.8/1000 person-months. Of the 10 confirmed EHS cases (9 males, 1 female; age = 23.4 ± 2.7 yrs; BMI = 25 ± 2; body fat = 13 ± 5%), 8 trainees had a peak ECT reading below 39.7°C which resulted in a sensitivity of 20%, specificity of 98.9%, positive likelihood ratio (LR) of 18.93 (95% Confidence Interval [CI] 5.5-65.6), and a negative LR of 0.81 (95% CI 0.6-1.1).

CONCLUSION

ECT had substantial false positive and negative rates. Further studies are needed to validate this technology in other populations, and the algorithm used in this device needs to be refined to better capture the environmental and physical requirements in the special operations population.

Relationship Between Running Biomechanics and Core Temperature Across a Competitive Road Race

BACKGROUND

Outdoor races introduce environmental stressors to runners, and core temperature changes may influence runners' movement patterns. This study assessed changes and determined relationships between sensor-derived running biomechanics and core temperature among runners across an 11.27-km road race.

HYPOTHESIS

Core temperatures would increase significantly across the race, related to changes in spatiotemporal biomechanical measures.

STUDY DESIGN

Cross-sectional cohort study.

LEVEL OF EVIDENCE

Level 3.

METHODS

Twenty runners (9 female, 11 male; age, 48 ± 12 years; height, 169.7 ± 9.1 cm; mass, 71.3 ± 13.4 kg) enrolled in the 2022 Falmouth Road Race were recruited. Participants used lightweight technologies (ingestible thermistors and wearable sensors) to monitor core temperature and running biomechanics throughout the race. Timestamps were used to align sensor-derived measures for 7 race segments. Observations were labeled as core temperatures generally within normal limits (<38°C) or at elevated core temperatures (≥38°C). Multivariate repeated measures analyses of variance were used to assess changes in sensor-derived measures across the race, with Bonferroni post hoc comparisons for significant findings. Pearson's r correlations were used to assess the relationship between running biomechanics and core temperature measures.

RESULTS

Eighteen participants developed hyperthermic core temperatures (39.0°C ± 0.5°C); core temperatures increased significantly across the race (P < 0.01). Kinetic measures obtained from the accelerometers, including shock, impact, and braking g, all significantly increased across the race (P < 0.01); other sensor-derived biomechanical measures did not change significantly. Core temperatures were weakly associated with biomechanics (|r range|, 0.02-0.16).

CONCLUSION

Core temperatures and kinetics increased significantly across a race, yet these outcomes were not strongly correlated. The observed kinetic changes may have been attributed to fatigue-related influences over the race.

CLINICAL RELEVANCE

Clinicians may not expect changes in biomechanical movement patterns to signal thermal responses during outdoor running in a singular event.

Technology Innovation and Guardrails in Elite Sport: The Future is Now

A growing number of companies are developing or using wearable sensor technologies that can monitor, analyse and transmit data from humans in real time that can be used by the sporting, biomedical and media industries. To explore this phenomenon, we describe and review two high-profile sporting events where innovations in wearable technologies were trialled: the Tokyo 2020 Summer Olympic Games (Tokyo 2020, Japan) and the 2022 adidas Road to Records (Germany). These two major sporting events were the first time academic and industry partners came together to implement real-time wearable solutions during major competition, to protect the health of athletes competing in hot and humid environments, as well as to better understand how these metrics can be used moving forwards. Despite the undoubted benefits of such wearables, there are well-founded concerns regarding their use including: (1) limited evidence quantifying the potential beneficial effects of analysing specific parameters, (2) the quality of hardware and provided data, (3) information overload, (4) data security and (5) exaggerated marketing claims. Employment and sporting rules and regulations also need to evolve to facilitate the use of wearable devices. There is also the potential to obtain real-time data that will oblige medical personnel to make crucial decisions around whether their athletes should continue competing or withdraw for health reasons. To protect athletes, the urgent need is to overcome these ethical/data protection concerns and develop wearable technologies that are backed by quality science. The fields of sport and exercise science and medicine provide an excellent platform to understand the impact of wearable sensors on performance, wellness, health, and disease.

An Emotion-Driven Vocal Biomarker-Based PTSD Screening Tool

Goal: This paper introduces an automated post-traumatic stress disorder (PTSD) screening tool that could potentially be used as a self-assessment or inserted into routine medical visits to aid in PTSD diagnosis and treatment. Methods: With an emotion estimation algorithm providing arousal (excited to calm) and valence (pleasure to displeasure) levels through discourse, we select regions of the acoustic signal that are most salient for PTSD detection. Our algorithm was tested on a subset of data from the DVBIC-TBICoE TBI Study, which contains PTSD Check List Civilian (PCL-C) assessment scores. Results: Speech from low-arousal and positive-valence regions provide the highest discrimination for PTSD. Our model achieved an AUC (area under the curve) of 0.80 in detecting PCL-C ratings, outperforming models with no emotion filtering (AUC = 0.68). Conclusions: This result suggests that emotion drives the selection of the most salient temporal regions of an audio recording for PTSD detection.

Biomarkers for warfighter safety and performance in hot and cold environments

Exposure to extreme environmental heat or cold during military activities can impose severe thermal strain, leading to impairments in task performance and increasing the risk of exertional heat (including heat stroke) and cold injuries that can be life-threatening. Substantial individual variability in physiological tolerance to thermal stress necessitates an individualized approach to mitigate the deleterious effects of thermal stress, such as physiological monitoring of individual thermal strain. During heat exposure, measurements of deep-body (T_c) and skin temperatures and heart rate can provide some indication of thermal strain. Combining these physiological variables with biomechanical markers of gait (in)stability may provide further insight on central nervous system dysfunction - the key criterion of exertional heat stroke (EHS). Thermal strain in cold environments can be monitored with skin temperature (peripheral and proximal), shivering thermogenesis and T_c. Non-invasive methods for real-time estimation of T_c have been developed and some appear to be promising but require further validation. Decision-support tools provide useful information for planning activities and biomarkers can be used to improve their predictions, thus maximizing safety and performance during hot- and cold-weather operations. With better understanding on the etiology and pathophysiology of EHS, the microbiome and markers of the inflammatory responses have been identified as novel biomarkers of heat intolerance. This review aims to (i) discuss selected physiological and biomechanical markers of heat or cold strain, (ii) how biomarkers may be used to ensure operational readiness in hot and cold environments, and (iii) present novel molecular biomarkers (e.g., microbiome, inflammatory cytokines) for preventing EHS.

Exertional heat stroke: An evidence based approach to clinical assessment and management

NEW FINDINGS

What is the topic of this review? The treatment of exertional heat stress, from initial field care through the return-to-activity decision, is reviewed. What advances does it highlight? Clinical assessment during field care using AVPU and vital signs to gauge recovery Approaches to field cooling and end of active cooling Shared clinical decision making for return to activity recommendations ABSTRACT: Exertional heat stroke (EHS) is a potentially fatal condition characterized by central nervous system dysfunction and body temperature often but not always >40°C that occurs in the context of physical work in warm or hot environments. In this paper, we review the continuum of care, from initial recognition and field care to transport and hospital care, and finally return to duty considerations. Morbidity and mortality can be greatly reduced if not eliminated with prompt recognition and aggressive cooling. If medical personnel are not present at point of collapse during or immediately following exercise, EHS should be the presumptive diagnosis until a formal diagnosis can be determined by qualified medical staff. EHS is the rare medical situation where initial treatment (cooling) takes precedence over transport to a medical facility, where advanced medical care may be required for severe EHS casualties. Recovery from EHS and return to activity is usually straightforward and unremarkable provided the casualty is rapidly cooled at time of collapse and adequate time is allowed for body healing. However, evidence-based data to guide return to activity following EHS is limited. Current research suggests that most individuals recover completely within a few weeks though some individuals may suffer prolonged sequalae and additional evaluation may be warranted, including heat tolerance testing. Several aspects of the care of the EHS casualty are based on best practices derived from personal experience and continued research is necessary to optimize evaluation and management. This article is protected by copyright. All rights reserved.