Seasonal changes in wildland firefighter fitness and body composition

Hiking with a pack is the highest-intensity task that wildland firefighters (WLFFs) perform during sustained activities related to wildland fire suppression. Firefighters perform this and other tasks together as a crew; this provides a unique model to evaluate select physical and physiological changes in members of working crews over a fire season during extended operations. The objective of this study was to evaluate changes in peak aerobic fitness (VO₂peak), sustainable aerobic fitness at the ventilatory threshold (VO₂vt) and body composition over a 5-month wildland fire season. WLFFs from four crews (55 males, 10 females) participated in a maximal graded exercise treadmill test and body composition evaluation pre- and post season. VO₂peak values and variance did not change across the fire season (pre = 3.96 ± 0.65, post = 3.96 ± 0.69 L min^-1, not significant). VO₂vt average decreased slightly while variance decreased greatly within each crew (pre = 37.5 ± 7.0, post = 35.4 ± 2.3 mL kg^-1 min^-1, P < 0.05). There was an improvement in VO₂vt in initially less-fit WLFFs and a VO₂vt decrease in initially more-fit WLFFs. WLFFs lost fat mass (-1.56 ±-1.06 kg, P < 0.01) and fat-free mass (-0.38 ±-1.24 kg, P < 0.05). Post-season VO₂vt values were the same as the higher range of the documented metabolic cost of uphill load carriage and reveal a unique group adaptation to extended physical demands.