Effects of Heat Exposure from Live-Burn Fire Training on Postural Stability of Firefighters

Firefighters perform physically intensive jobs in suboptimal environments, making it even more important for them to maintain good functional postural balance or stability. As part of their training, firefighters are required to perform physically demanding tasks under high stress and high heat environments. These demanding tasks lead to increased physical fatigue which can then result in poor performance and/or postural instability. The objectives of this study were to 1) investigate the effect of live-firefighting training-induced heat stress on static postural balance, and 2) investigate the association between commonly monitored physiological responses (core body temperature, heart rate, oxygen saturation and blood pressure) and measures of static postural balance. Twenty-six firefighters (mean ± SD: age 36.0 years ±5.2, weight 216 lbs. ± 34, BMI 29.7 ± 4.2) participated in live firefighting training 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 wearable 3-D 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 outcome variables from 3-D wearable sensors were used to create 3-D Phase-Plane based postural stability metrics. Physiological measurement of core body temperature (CBT) (measured with a radio pill) as well as perception of heat increased significantly during the live fire-training exercise. In addition, firefighters also perceived an increase in physical fatigue and respiratory distress. Angular combined stability parameters (ACSP), RMS angular velocity around ML axis were significantly correlated with CBT. In the multivariate analysis adjusted for the scenarios, height and weight of the firefighters, these measures of static postural balance were significantly associated with CBT. As per the model results, static postural balance, as indicated by ACSP, worsened with an increase in CBT. Future studies should place sensors at body extremities along with close to center of mass to capture the kinematic movements more comprehensively influencing postural balance.