Objective: The Finnmarksløpet dogsled race lasts up to 7 days. Helpers, who keep time, coach, and transport equipment, have to be alert though they have little and fragmented sleep. This study investigated disruptions of the rest-activity rhythm among helpers.
Methods: 10 helpers were monitored by actigraph a week before, during, and after the race. Sleep logs, sleepiness rate, and self-reported quality of sleep were collected.
Results: Nonparametric circadian rhythm analysis showed significant differences between the pre- and postrace interdaily stability and amplitude of rhythm. Compared to prerace, sleepiness at bedtime was increased and number of nocturnal awakenings was reduced postrace, although the actigraphic outputs showed no improvement in sleep quality. Helpers who were engaged in the race for a longer span (5-6 days) had more difficulty recovering from the sleep loss accumulated during the race than those engaged for a shorter time (2-3 days).
Conclusion: Poor sleep combined with prolonged and demanding mental focus for 2 days or more has a negative influence upon the rest-activity cycle, though complete restoration of the cycle occurs over 1 week or more. Being in such a condition for ≥ 5 days leads to disruptions of the circadian component of the sleep-wake cycle that hampers the sleep recovery process. Disrupted sleep and demanding mental requirements are common in long-distance sporting events as well as among shift workers. Follow-up intervention should be made in such cases to ensure the return of a healthy rest-activity rhythm and sleep quality.
Keywords: actigraphy; circadian rhythms; rest–activity cycle; sleep loss; sleep patterns.