• Immune Function and Shift Length
• Fitness and Fatigue
• Sleep Deprivation

This study compared the reduction in salivary IgA (sIgA) in response to a 14- or 21-hour work shift. Salivary IgA is the first line of defense against respiratory infection. Seventeen wildland firefighters (15 men and 2 women) from two interagency hotshot crews were tested. Subjects were studied in response to a short (13.9 ± 0.7 hours) or a long (21.4 ± 0.3 hours) work shift (table 1). Energy expenditure during a work shift was estimated using the method established by Heil (2001). Unstimulated saliva was collected for 4 minutes before work at 0530 and immediately after a shift. The firefighters' salivary IgA secretion rate (micrograms per minute) was calculated from an ELISA assay procedure.

Results—The energy expenditure during the long work shift was significantly higher (p < 0.05, 4,101 ± 578 kilocalories) compared to the short work shift (3,322 ± 478 kilocalories).

Salivary IgA was significantly decreased after the work shift but had returned to the values recorded before the shift by the following morning in both groups. The 14-hour work shift group showed a recovery in sIgA (morning values at days 5 and 6 were 85.8 ± 40.5 and 67.4 ± 32.0 micrograms per minute, respectively). In contrast, the 21-hour work shift group showed suppressed values for sIgA (27.3 ± 13.3 micrograms per minute) 6 days after the extended shift (figures 1 and 2).

Figure 1—Changes in salivary IgA in response to a single work shift of 13.9± 0.7
hours (n = 6). The summary data for the fatigue index are also shown (heart rate
response to a 1-minute step test). These data indicate adequate recovery
after the single work shift.

Figure 2—Changes in salivary IgA secretion rate in response to a single work
shift of 21.4 ± 0.3 hours (n = 11) followed by 5 days of 14 ± 0.7-hour shifts.
Although subjects demonstrate an acute recovery response, sIgA secretion
rate is still suppressed 6 days after the 21-hour shift in comparison to the
rate after a 14-hour work shift.

Conclusions—These data indicate that the sIgA secretion rate is significantly depressed after a single day of wildfire suppression. The energy expended during a work shift in combination with the shift's duration may impair recovery and increase the risk for upper respiratory infection during extended operations.

Ruby, B.; Gaskill, S.; Heil, D.; Sharkey, B.; Hansen, K.; Lankford, D., 2002. Changes in salivary IgA during arduous wildfire suppression relative to work shift length. Medicine and Science in Sports and Exercise. 34:s195 (study supported by MTDC).

This study investigated work and recovery rates in wildland firefighters with differing levels of sustainable aerobic fitness. Eleven wildland firefighters from an interagency hotshot crew served as subjects. Subjects were grouped by levels of sustainable fitness as measured by oxygen intake at the ventilatory threshold and studied in response to work rates and recovery after single or multiple arduous days of wildland fire suppression (table 2). Work shift energy expenditure was estimated using the method established by Heil (2001). Recovery rates were measured using a submaximal heart rate (fatigue) index.

Work and recovery rates for 11 wildland firefighters who had low or high sustainable fitness, energy expenditure and change in heart rate index were compared (figure 3).

Figure 3—This graph shows the work (kilocalories per day) done by a hotshot crew
over a 9-day period. The crew was divided into fit and less fit groups. The fit group
did more work per day than the less fit group.

Conclusions—Wildland firefighters with higher sustainable fitness (40 to 49 milliliters per kilogram-minute VO2) are able to do more absolute work and more work relative to their body weight during each day of a duty cycle compared to less fit firefighters (30 to 39 milliliters per kilogram-minute VO2). Fit individuals recovered more quickly after multiple days of arduous work despite higher energy expenditures. Because the less fit group met or exceeded the minimal job-specific fitness requirements for wildland firefighting (the pack test), these data suggest that the current fitness requirements may need review. Increased sustainable fitness improves work output and recovery.

Gaskill, S.; Ruby, B.; Heil, D.; Sharkey, B.; Hansen, K.; Lankford, D. 2002. Fitness, work rates, and fatigue during arduous wildfire suppression. Medicine and Science in Sports and Exercise, 34:s195 (study supported by MTDC).

This study compared the effects of sleep loss with the effects of alcohol intoxication on subjects' performance during a hand-eye coordination test. Forty subjects tracked a moving circle on a computer screen at thirty-minute intervals after 28 hours of sleep deprivation or after ingesting 10 to 15 grams of alcohol at 30-minute intervals until their blood alcohol level reached 0.10 percent. During the first 12 hours of sustained wakefulness (8 a.m. to 8 p.m.), tracking performance improved 1 to 2 percent above the starting level; performance then declined to a low of 6 percent below the starting level. The decline occurred from 8 p.m. to 8 a.m., physiologically the lowest period for human performance. Performance rebounded to near starting levels during the final hours of sleep deprivation.

After 24 hours of sustained wakefulness, performance on the tracking task decreased to a level equivalent to the performance deficit observed at a blood-alcohol concentration of 0.10 percent, which meets or exceeds the definition of intoxication in all States. The authors suggest that the "blood-alcohol equivalent" may provide policymakers with an easily grasped index of the relative impairment associated with sleep loss. (Dawson, D.; Reid, K. 1997. Fatigue, alcohol, and performance impairment. Nature. 388: 235.)

Editor's Note: While performance on the simple tracking task declined overnight, it rebounded in the morning after 28 hours of sleep deprivation, confounding the relationship to blood alcohol. The analogy to alcohol impairment may make sense for pilots or even bus drivers (where the relationship to tracking tasks holds), but it does not reflect cognitive performance or decisionmaking in wildland firefighting.