Wearable physiological monitoring for human thermal-work strain optimization

Abstract

Safe performance limits of soldiers and athletes have typically relied on predictive work-rest models of ambient conditions, average work intensity, and characteristics of the population. Bioengineering advances in noninvasive sensor technologies, including miniaturization, reduced cost, power requirements, and comfort, now make it possible to produce individual predictions of safe thermal-work limits. These precision medicine assessments depend on the development of thoughtful algorithms based on physics and physiology. Both physiological telemetry and thermal-strain indexes have been available for >50 years, but greater computing power and better wearable sensors now make it possible to provide actionable information at the individual level. Core temperature can be practically estimated from time series heart rate data and, using an adaptive physiological strain index, provides meaningful predictions of safe work limits that cannot be predicted from only core temperature or heart rate measurements. Early adopters of this technology include specialized occupations where individuals operate in complete encapsulation such as chemical protective suits. Emerging technologies that focus on heat flux measurements at the skin show even greater potential for estimating thermal-work strain using a parsimonious sensor set. Applications of these wearable technologies include many sports and military training venues where inexperienced individuals can learn effective work pacing strategies and train to safe personal limits. The same strategies can also provide a technologically based performance edge for experienced workers and athletes faced with novel and nonintuitive physiological challenges, such as health care providers in full protective clothing treating Ebola patients in West Africa in 2014. NEW & NOTEWORTHY This mini-review details how the application of computational techniques borrowed from signal processing and control theory can provide meaningful advances for the applied physiological problem of real-time thermal-work strain monitoring. The work examines the development of practical core body temperature estimation techniques and how these can be used in combination with current and updated thermal-work strain indexes to provide objective state assessments and to optimize work rest schedules for a given task.

Heat Adaptation in Military Personnel: Mitigating Risk, Maximizing Performance

“…Whether it would always be operationally effective to strictly observe sub-maximal physiological thresholds is a matter of military debate, at least as it applies to routine training in the heat (Hunt et al, 2016). Attaining measures of heart rate, Tc or derived/composite parameters such as the Physiological Strain Index (Buller et al, 2018) could ensure FIGURE 1 | Heat adaptation in 21 volunteers, displayed as progress toward full (100%) acclimatization status on Day 23 in Cyprus, relative to pre-deployment baseline in United Kingdom (0% acclimatized). Volunteers performed the acclimatization protocol described in Table 1, with 60 min stepping at 50% VO 2 max in a climatic chamber controlled to WBGT 34 • C, at United Kingdom baseline and on Days 2, 6, 9, and 23 following arrival in Cyprus (substituted for usual acclimatization exercise on these days).…”

Military applications of soldier physiological monitoring

“…A third aspect of improving practical but reliable individual estimates of TWS limits has been the development of an adaptive TWS index. 3 The Army National Guard Bureau is an early adopter of this enhanced capability, using RT-PSM technology to closely monitor limits of individuals performing critical tasks while encapsulated in protective suits in specialized operations by their Weapons of Mass Destruction Civil Support Teams (WMD-CST). 4 Personalized monitoring in hot training environments is also being investigated, where it could improve training effectiveness by permitting higher training workloads than might be predicted by group-based predictive heat strain models.…”

“…2 In this example of thermal-workload limits, real time physiological status monitoring (RT-PSM) now provides new military capability with individual assessment of soldier performance limits. 3,4 The technological advance has come about by turning the focus inward, to consider the actual state of an individual, instead of extrapolating from external conditions and assuming typical responses. Thermalwork strain monitoring is one of the first military PSM applications to be used outside of the research community but provides only one example of near term uses (Table 1).…”

Emerging Ergonomics Issues and Opportunities in Mining

“…While data fusion can provide a better representation of a worker’s activity or environment, in some situations multiple devices may be worn and methods to evaluate multi-sensor data need to be considered [ 25 , 26 ]. Similarly, complex algorithms can be used to estimate risks in industry, such as worker whole-body fatigue [ 27 ], heat stress [ 28 ], fall risk [ 18 ], and real-time assessment of risky postures [ 29 ]. Future research will need to test the accuracy of the algorithms, combine multi-sensor data to evaluate mining tasks, and develop sensors that can collect the required data in a comfortable and durable unit fit for the mining industry.…”