Army

Wearable bio-sensors, algorithm for heat acclimation

Wearable calculates an adaptive physiological strain index and allows individuals to self-monitor thermal strain for the most efficient acclimatization exercises within the time available

Software & Information Technology Medical & Biotechnology Electronics

U.S. Army scientists have recently developed a wearable system to help users acclimate to hot environments. The patented technology is available via patent license agreement to companies that would make, use, or sell it commercially.

Heat stress results from the interaction of temperature, humidity, solar radiation, physical work rate, and the wearing of heavy clothing and equipment. While it’s a concern for anyone working in the heat, it’s of particular issue for warfighters, firefighters, hazard material handlers, welders, and athletes wearing significant protective gear. Heatstroke can lead to hospitalizations and even fatalities. These occurrences are at least partially the result of a lack of exposure to the hot environments under physical strain. But it is possible to acclimatize one’s self to heat exposure – if done under the appropriate conditions and closely monitored.

However, defining the appropriate workout conditions and close, accurate monitoring of a person’s physical state is absolutely critical to effectively adapting the body to higher heat indices. Conditions include the level of the heat index, the intensity of the work being performed, frequency of the adaptation sessions and their duration. Monitoring includes heart rate, skin temperature, and calculated core temperature. Pulse oximetry and accelerometer data may also be used.

Army researchers have developed a smartwatch for providing acclimatization guidance to an individual user. The system includes a chest strap having a heart rate monitor and a skin temperature sensor. Electronic sensors in the wrist unit receive a heart rate signal and skin temperature and calculate a physiological strain index (PSI).

A chest-strap sensor is part of the system. (Army photo)

Algorithms interpolate the heart rate to core body temperature. This is checked against the timed training period to deliver a readout of where the person is in the workout and at what level of the strain he or she is experiencing. With the inclusion of accelerometer data, the system provides pacing information to the user so that he or she can maintain a target PSI. Data is interpreted relative to the user’s age, resting and critical core temperature, and resting and critical heart rate.

Repeated workouts at target PSIs acclimatize the person and enhance performance during subsequent heat exposure. This is seen in increased stroke volume, reduced heart rate, reduced core and skin temperature, increased sweat rate, more dilute sweat, and better maintenance of plasma volume and peripheral blood flow compared with exercising at the same intensity in the unacclimated state.

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