Psychomotor performance of truck drivers before and after day shifts

The aim of the present study is to evaluate the psychomotor performance of professional drivers in a field setting and in relation to certain variables, including age, behavioral factors, urinary levels of 6-sulfatoxymelatonin (aMT6s) normalized to urinary creatinine excretion, and the characteristics of the work shifts.

The study was carried out on 16 professional male truck drivers aged 34-53 years. The drivers were submitted to the Vienna Reaction Test (RT) and Vienna Determination Test (DT) and provided urine specimens before and after 39 work shifts. They were also asked to record the road and traffic conditions (motorways, suburban and urban roads, traffic jams, visibility), duration, and mileage for each driving shift.

Using the 50th percentile as a cut point to arbitrarily categorize the performance measurements (Vienna RT reaction time and motor time, Vienna DT reaction time and number of correct reactions) into low and high performance levels, a direct relation emerged between the risk of low performance levels, as assessed by RT reaction time and motor time, and morning urinary levels of aMT6s categorized by tertiles. Before the driving shifts, the odds ratios of low performance levels (adjusted for start time and age) were 8.39 (95% confidence interval [CI]: 1.23-57.10) in the highest tertile compared to the lower tertile of aMT6s for RT reaction time and 4.15 (95% CI: 1.26-13.65) for RT motor time, respectively. After driving shifts, negative age-related effects on motor performance were detected. Multiple linear regression analyses, performed using early morning urinary aMT6s levels, age, and driving shift characteristics (start time, duration of driving shift) as predictors of performance measurements, showed aMT6s levels to be the primary independent predictor of RT reaction time before driving shifts and age as the primary predictor of RT motor time after driving shifts. No correlation was found between the risk of low performance levels as assessed by Vienna DT (reaction time and number of correct reactions) and aMT6s levels.

The wide interindividual variability of urinary aMT6s excretion observed before driving shifts and the direct association between aMT6s levels in the early morning and performance measurements suggest that the circadian typology of drivers should be taken into account when scheduling the work shifts of professional drivers.