The psychological consequences of shifts will be assessed in terms of perceived stress and fatigue using visual analog scales. Potential biomarkers will be assessed through urine and saliva collections. Heart rate variability will be measured using 5-lead electrocardiogram. Psychological questionnaires will be completed only once during the control day. The workload during each shift will be estimated by: the total number of entries, the number of admissions, the number of outpatients (collected by computer), and the number of life-and- death emergencies (given by the emergency physician). Sleep duration, including naps, will be assessed by questionnaire (bed time - wake time) on the three-day tracking of each shift and on the control day.