EVALUATION OF AIR CONSUMPTION AND WORK EFFICIENCY IN STRUCTURAL FIREFIGHTERS

INTRODUCTION: For safe and efficient fireground performance, firefighters (FF) must consume air supplied by the self-contained breathing apparatus (SCBA) efficiently while sustaining high work rates. Firefighter research and fire department physical ability assessments typically quantify performance solely on task completion time (i.e., work rate), failing to consider the critical element of air consumption efficiency, which subsequently impacts the SCBA’s functional work duration. PURPOSES: (Arm 1, Aim #1) To examine variability in air consumption (AC) between FF during standardized pace tasks; (Arm 1, Aim #2) To evaluate AC efficiency (ACE) against a recognized metabolic-work rate concept of economy; (Arm 1, Aim #3) To identify fitness, anthropometric, and physiological parameters associated with ACE; (Arm 1, Aim #4) To evaluate the relationship of ACE and self-paced work rate; (Arm 2, Aim #5) To evaluate the reliability and variability of a recently introduced “work efficiency” (WE) performance metric reflective of both work rate and AC; (Arm 2, Aim #6) To explore the relationship between WE and known measures of metabolic strain; (Arm 2, Aim #7) To identify fitness, anthropometric, and demographic correlates of WE. METHODS: Structural FF completed at least one randomized trial of an AC drill (ACD) while breathing through a SCBA (ACDSCBA; Arm 1, N=40; Arm 2, N=79) and/or a portable gas analyzer (ACDV̇O2; Arm 1, N=40; Arm 2, N= 44). Specifically, in Arm 1, FF performed the ACD at a standardized pace, with a subsample (n=11) completing an additional trial at a self-selected pace. In Arm 2, FF performed the ACD at a self-selected pace. The change in SCBA pressure was measured from ACDSCBA and ventilatory outcomes were monitored during ACDV̇O2. Fitness and anthropometric data were collected separately. All data were analyzed with descriptive statistics, paired-samples t-tests, and effect sizes. For Arm 1, reliability was assessed with intraclass correlation coefficients. Variability was assessed with measures of dispersion and correlations assessed relationships between ACE versus economy, strain, fitness, anthropometrics, and self-selected ACD time outcomes. For Arm 2, correlations were assessed between WE (WE = (1 / (ACD time (min) x cylinder pressure change (min·lb·in-2)))x 104) versus strain, anthropometric and fitness outcomes. Multiple linear regression was conducted to identify the strongest predictors of WE. RESULTS: In Arm 1, during the standardized pace ACD, the average inter-FF AC variability (±1 SD) was 13.7% of cylinder usage, extrapolating to ~3.1 min of variability in work duration per cylinder. ACE was correlated with work economy as well as numerous anthropometric and physiological outcomes, but not with self-paced ACD time. In Arm 2, WE yielded acceptable reliability (ICC=0.71) and yielded substantial inter-firefighter variability (0.79±0.25 ((min·lb·in-2)-1)x104; Coefficient of variation=32%). WE was positively correlated to oxygen consumption (L·min-1, mL·kg-1·min-1) and tidal volume, and negatively correlated to the ventilatory equivalent for oxygen and respiratory frequency. Multiple fitness, anthropometric, and demographic attributes were correlated to WE, with height, upper-body endurance, and aerobic endurance serving as the strongest predictors. CONCLUSIONS: At standardized work rates, FF performing at higher internal loads demonstrated poorer ACE. Improving metabolic work tolerance and reducing excessive load carriage may improve ACE to extend the SCBA’s functional work duration. However, WE may be a more appropriate metric, as it accounts for critical occupational performance factors of work rate and AC. FF may enhance WE through comprehensive physical training focused on improving anaerobic, upper body, and aerobic endurance outcomes