Glycogen levels in wildland firefighters during wildfire suppression

Objective The purpose of this project was to determine the effects of wildfire suppression on muscle glycogen utilization in wildland firefighters (WLFFs). Methods Wildland firefighters (n = 11) participated in the study. Muscle biopsies were obtained from the vastus lateralis pre- and post-work shift. Activity patterns were measured using an Actical activity monitor positioned on the chest. Food was consumed ad libitum and recorded using a food log and interview. Differences were analyzed using paired samples t-tests and relationships were assessed using Pearson r correlation coefficients. A significance level of p < .05 was set. Results Body weight was similar pre- to post-work shift (85.9 ± 9.1 and 85.6 ± 8.8 kg, respectively). Muscle glycogen decreased from pre- to post-work shift, 101 ± 7 to 80 ± 5 mmol/kg wet wt, p < .05. Average activity counts were 175 ± 60 counts/min. Mean percent of time spent in each intensity category included: sedentary (74 ± 7%), light (21 ± 5%), and moderate/vigorous (5 ± 2%). There was a significant relationship between minutes completing vigorous activity and glycogen utilization (r = -.76, p < .05), and between minutes spent completing vigorous activity and pre-shift glycogen content (r = .79, p < .05). Kilocalorie intake during the work shift was 9.2 ± 2.9 MJ/d (2195 ± 699 kcal/d). Conclusions This study demonstrates the variety of self-selected nutritional and activity habits of WLFFs, and emphasizes the relationships between moderate/vigorous activity and muscle glycogen. The current data suggest that the food provided was adequate to maintain muscle glycogen levels pre- to post-work shift.