Objective: Measure the effect of physically demanding tasks performed under hot environment on postural balance characteristics of firefighters.
Design: The study design is to evaluate the impact of heat stress on postural balance of firefighters during live burn training using wearable, wireless, multi-dimensional gyroscopes and accelerometers. Heat stress and physical exertion levels will be quantified using a wearable sensors system: “Bioharness,” and an FDA approved ingestible radio pill (CoreHQ). These wearable sensors will provide firefighters’ heart rate and core body temperature during live burn training. Collectively, these outcomes will be used to assess the physiological effects of heat stress on firefighters.
Method: Twenty-six firefighters participated in live firefighting training (mean ± SD: age 36.0 years ± 5.2, weight 216 lbs ± 34, BMI 29.7 ± 4.2) while performing following tasks: search and rescue, hose advancement, and backup. Prior to heat exposure (PRE) and following each scenario (POST1, POST2, POST3), firefighters’ postural balance was assessed with a lightweight, wearable inertial sensor system quantifying time dependent changes in linear acceleration (LIN ACC) and angular velocity (AV) about three orthogonal axes [Anterior-Posterior (AP), Medial-Lateral (ML), and vertical (V)] during one foot balance tests for 30 seconds under eyes open and eyes closed conditions. The data obtained were processed by creating phase plane plots between AV and angular displacement (AD) as well as linear ACC and linear velocity (LIN VEL). The postural balance characteristics were quantified by the size (max excursions) of the phase plane plots, and set of stability metrics based on the root mean square (RMS) and variance of AD and AV, as well as the total sway area (SA) and sway length (SL) of each test. Perceived ratings of physical exertion (PE), thermal compensation(TS), and respiratory distress (RD) as well as core body temperature and heart rate metrics were also collected prior to and following each scenario.
Results: Seven of the balance parameter mean values, for all firefighters, were found to significantly increase from baseline tests to POST3 tests (p < 0.05): RMS LIN VEL about ML axis, RMS AD about AP axis, LIN DSP along ML axis, Excursion of LIN VEL along ML axis, Excursion of AD about AP axis, SL LIN VEL versus ACC along V axis, and SA LIN VEL versus ACC along AP axis. There was no correlation between PE, TS, and RD perceived ratings and any balance parameter. Both core body temperature and heart rate values were positively correlated with PE, TS, and RD ratings, but were not correlated with any balance parameter.
Conclusion: Significant increases in stability parameter, excursion, and RMS response about the ML and AP axis, associated with tasks performed in hot environments, suggest an increase in postural instability, larger postural sway and increased efforts to maintain balance. These increased postural instability outcomes may increase their risk of falling. Perceived exertion parameters did not correlate with any balance parameters, which suggests that a firefighter does not necessarily perceive postural instability, due to heat stress, leading to potential increased risk of falling.