The effect of sleep restriction and exposure to physical activity on the cognitive ability of volunteer firefighters across a 3-day simulated fire-ground tour

Aims: To determine the combined effects of concurrent days of physical work and sleep restriction on attention in a group of volunteer fire-fighters. Methods: Twenty-four volunteer fire fighters (Males, N=20, Females; N=4) were required to live in a simulated fire ground environment for four nights/five days. On the first night (adaption) participants were given 8 hours sleep opportunity, whereas on nights 2 and 3 sleep opportunity was restricted to 4 hours. On the last night (recovery) they were given 8 hours sleep opportunity. Physical activity circuits lasted 1 hour followed by a cognitive battery that included the measurement of vigilant attention using a 5-minute version of the Psychomotor Vigilance Task (PVT). The dependent variables were reciprocal reaction time and lapses as measured by PVT. Results: There was a significant main effect of day on reciprocal reaction time on the PVT, (F(2.65, 60.95)=9.69, p<.001), with significantly lower reciprocal reaction times on day 2 compared to day 1 (p<.001), and day 3 compared to recovery day, (p<.01). There was a significant main effect of day on lapses, (F(2.26, 52.05)=3.67, p<.05). Lapses were significantly lower on recovery than day 3 (p<.05). Discussion: Multiple nights of partial sleep restriction in combination with physical work leads to a reduction in attention. Further nights of similar sleep restriction is expected to lead to more dangerous declines in performance. Thus, it is imperative that firefighting agencies acknowledge that even one night of little sleep may lead to a decline in their ability to remain vigilant and respond rapidly to threatening situations. Unfortunately it is difficult to determine whether physical activity during the day adds to the effect of fatigue, or counteracts the influence of fatigue.