Fatigue is recognized as an important safety concern in the transportation industry. In this study, our goal was to investigate how circadian and sleep-wake dependent factors influence St-Lawrence River pilots' sleep-wake cycle, alertness and psychomotor performance levels at work. A total of 18 male St-Lawrence River ship pilots were recruited to a 16-21-day field study. Pilots' chronotype, sleepiness and insomnia levels were documented using standardized questionnaires. Their sleep-wake cycle was documented by a sleep-wake log and wrist-worn activity monitoring. Subjective alertness and objective psychomotor performances were assessed ~5×/day for each work and rest day. Ship transits were distributed throughout the 24-h day and lasted on average (± SEM) 5.93 ± 0.67 h. Main sleep periods occurred mainly at night, and objectively lasted 6.04 ± 1.02 h before work days. When going to bed at the end of work days, pilots subjectively reported sleeping 7.64 ± 1.64 h in the prior 24 h. Significant diurnal and wake-dependent effects were observed for subjective alertness and objective psychomotor performance, with minimum levels occurring between 09:00 and 10:00. Thus, despite their irregular work schedule, ship pilots presented, as a group, a diurnal variation of alertness and psychomotor performance indicative of a day-oriented circadian system. Important inter-individual differences were observed on psychomotor performance mesor and phase. In individuals, earlier phases in psychomotor performance were correlated with earlier chronotype. This study indicates that both circadian and homeostatic processes modulate alertness and psychomotor performance levels with worst levels reached when long shifts ended in the morning. This work has potential applications as it indicates fatigue countermeasures considering both processes are scientifically based.
Keywords: Marine pilots; chronotype; circadian rhythms; inter-individual differences; psychomotor performance; shift work; sleep–wake cycle; subjective alertness.