Core Temperature Wearables - Are We There Yet?

Given the advances in consumer wearable technology, it's a fair expectation that those advances would translate to wearables suitable for workers. Sure, occupational settings are more demanding in terms of the 'ruggedisation' required to operate in the hot and humid microclimate proximal to the body. But if heat-exposed workers are to be managed with input from a wearable device, the key requirement is accuracy. So, here's our take on three wearables currently on the market.

Body Thermometer

CORE by greenTEG AG

CORE claims to be the "only wearable non-invasive, continuous, and accurate Core Body Temperature monitoring solution", estimating core temperature from a rechargeable 5x4cm heat flux and skin temperature sensor (see below). The sensor is attached below the armpit by adhesive patch or a wearable band (like a heart rate monitor). The battery lasts for multiple days when transmitting and for weeks in stand-by mode. The product website claims that "the accuracy of CORE has been validated in an independent clinical study" and provides a "download" validation link that opens five slides from CORE spruiking accuracy but without the associated published independent research. Our disappointment was short-lived as independent research has been published regarding CORE accuracy. The study employed both cool and warm/hot environmental conditions for exercise that produced almost 12,000 data points, including many >38.5ºC, with the researchers stating that "the results obtained do not support the manufacturer’s claim that the CORE sensor provides a valid measure of core body temperature". You can read the full paper here.


Kenzen

Utilising a similar sized sensor (~5x6cm) to CORE that attaches to the upper arm with a band, Kenzen claims its system provides "continuous safety monitoring (that) is both real-time and highly accurate". Evidence is provided to support this claim but not in the form of independent research published in a peer-reviewed journal. The research is a Kenzen sponsored abstract from the Experimental Biology 2021 Meeting. Read the abstract here.


There's a large discrepancy between an abstract and a full research paper. Furthermore, the analysis of data described within the abstract is questionable. Data was collected every 5 minutes and was seemingly averaged each hour as per the graph below. For a product that claims to provide real-time safety monitoring, reporting accuracy based upon hourly data is a strange move. The accuracy of those real-time measurements should be reported and until that's done by independent research, the claim of accuracy cannot be substantiated.

Cosinuss°

Unlike the CORE and Kenzen options, Cosinuss° is an "in-ear" sensor with a battery life of up to 24hrs. Cosinuss° states "Our ergonomic wearables offer a more cost-effective and accurate alternative to the competition for measuring the following: blood oxygen saturation, core body temperature, heart rate, heart rate variability, respiratory rate and position/acceleration". Cosinuss° accuracy has been evaluated by an independent but small field trial of firefighters, with published results. Read the full paper here.


While the research would have benefitted from additional participants and more profound heat stress (maximal core temp of 38.4ºC), the authors concluded that "the validity of the Cosinuss° (C-med version) was not confirmed in this study". Interestingly, despite generally under-predicting core temperature, there was an instance where Cosinuss° core temperature was 40.1ºC. Note that Cosinuss° produce a range of in-ear monitors and that the results reported for C-med may not be representative of all models.


Summary

Despite our negative conclusions regarding the accuracy of the CORE, Kenzen and Cosinuss° (based upon available information), we have a vested interest in core temperature wearables, as they may contribute to management of worker heat stress in the field. We currently utilise ingestible pills that provide accurate core temperature data with the primary downside of being invasive. Other limitations include ingestion lead-time prior to monitoring, occasional delays for pill connectivity and worker monitoring capped by the associated hardware and therefore, cost. There's a need for non-invasive options and a lot of development has been, and will continue to be done in this space. We look forward to reporting if and when worker core temperature wearables are "field-ready".


References

Moyen N, Bapat R, Tan B, Esfahani M, Mundel T. Accuracy of a wearable device to non‐invasively predict continuous core body temperature. The FASEB Journal. 2021;35


Roossien, C.; Heus, R.; Reneman, M.; Verkerke, G. Monitoring core temperature of firefighters to validate a wearable non-invasive core thermometer in different types of protective clothing: Concurrent in-vivo validation. Appl. Ergon. 2020, 83, 103001


Verdel N, Podlogar T, Ciuha U, Holmberg H-C, Debevec T, Supej M. Reliability and Validity of the CORE Sensor to Assess Core Body Temperature during Cycling Exercise. Sensors. 2021; 21(17):5932