Wildland firefighter load carriage: effects on transit time and physiological responses during simulated escape to safety zone

Abstract

The purpose of this investigation was to determine the effects of load carriage on transit time during simulated escape route evacuation. Subjects (8 males, 5 females) completed two maximal field hikes in random order on two successive days (16 kg [35 lb] line gear pack trial and no pack trial). Subjects carried a fire shelter and a Pulaski (the most commonly used fireline construction tool in the United States, consisting of a hoe/ax combination with an 80 cm handle) during each trial. Trials were completed on a dirt trail 660.5 m in length with a vertical rise of 137 m (average grade = 20.75%). Expired air samples were analysed continuously during each trial (Cosmed K4 or Aerosport VO₂₀₀₀). Blood samples were collected before and 2 min after exercise for lactate analysis. Transit time was significantly faster during the No pack trial, representing a 21.5 and 26.3% faster transit time for males and females, respectively. For the males, mean VO₂ was higher during the No pack trial. The difference in blood lactate (peak–rest) was significantly higher during the Pack trial for the male subjects. High correlations between peak VO₂ (L min^–1) and transit rates were noted (r = 0.82 for the Pack trial and 0.87 for the No pack trial), indicating the contribution of aerobic fitness to transit time. These data suggest that escape routes should include a physical strain index related to load carriage, distance and slope and that line gear weight standards should be further evaluated.