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Understanding the effect of stress, fatigue, and sleep deprivation on the ability to maintain an alert and attentive state in an ecologically valid setting is of importance as lapsing attention can, in many safety-critical professions, have devastating consequences. Here we studied the effect of close-quarters battle (CQ battle) exercise combined with overnight military training with sleep deprivation on cognitive performance, namely sustained attention and response inhibition. In addition, the effect of the CQ battle and overnight training on cardiac activity [heart rate and root mean square of the successive differences (RMSSD)] during the cognitive testing and the relationship between cardiac activity and cognitive performance were examined. Cognitive performance was measured with the psychomotor vigilance task (PVT) and the sustained attention to response task (SART). Altogether 45 conscripts participated in the study. The conscripts were divided into control (CON) and experimental (EXP) groups. The CON completed the training day after a night of sleep and the EXP after the overnight military training with no sleep. Results showed that the effect of the overnight training on cognitive performance and the between-group difference in heart rate (HR) and heart rate variability (HRV) depended on the cognitive test. Surprisingly, the cognitive performance was not largely affected by the CQ battle. However, as expected, the CQ battle resulted in a significant decrease in RMSSD and an increase in HR measured during the cognitive testing. Similarly, the HR parameters were related to cognitive performance, but the relationship was found only with the PVT. In conclusion, fatigue due to the overnight training impaired the ability to maintain sufficient alertness level. However, this impairment in arousal upregulation was counteracted by the arousing nature of the SART. Hence, the conscripts' cognitive performance was mainly preserved when performing a stimulating task, despite the fatigue from the sleep loss of the preceding night and physical activity. publishedVersion

Identifying the causes of sleepiness in various safety-critical work environments is neces-sary for implementing more efficient fatigue management strategies. In transportation, little is known about drivers' own perceptions of these causes. Therefore, we instructed shift-working tram (n = 23) and long-haul truck drivers (n = 52) to report at the end of their shifts what made them sleepy if they felt so. These self-reports, measured on-duty sleepiness, and sleep amounts were recorded on every shift over a period of 2-3 weeks per driver. The causes of sleepiness were queried with smartphone applications and sleep logs. Sleepiness was measured with the Karolinska Sleepiness Scale (KSS) and sleep with wrist-worn actigraphs. Data were analyzed using generalized estimating equations. Sleep loss and insufficient rest breaks were commonly reported as causing sleepiness among the tram drivers, whereas time of day and sleep loss were the leading causes among the truck drivers. Other causes, such as traffic or cabin conditions, were not frequently men-tioned. During morning, day, and evening shifts, the truck drivers were less likely to report insufficient rest breaks as causing sleepiness than the tram drivers. Similarly, during morn-ing shifts, the truck drivers were less likely to attribute their sleepiness to sleep loss. In shifts with drives reporting severe sleepiness (KSS > 7 at least once, 18-21% of shifts), sleep loss was significantly reported as causing sleepiness among both groups. Reporting insuf-ficient rest breaks was associated with severe sleepiness among the tram drivers, whereas time of day showed the same among the truck drivers. The results highlight the need for addressing sleep-related fatigue in transportation and provide directions for future research with regard to secondary causes of sleepiness . (c) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Sleep loss is known to contribute to road traffic accidents. Professional drivers are vulnerable to curtailment of sleep due to long driving bouts and shift work. To fill in the gap in the literature related to the buildup of sleep loss in irregular shift systems, we recorded the sleep and working hours of 47 shift-working long-haul truck drivers during a two-week period. Sleep (time in bed) was verified by actigraphy and sleep logs. Sleepiness was measured using the Karolinska Sleepiness Scale (KSS). Individual sleep need was based on self-assessments. We examined the accumulated sleep versus self-reported sleep need across the study period, using midnights as points of observation, and the accumulated sleep loss within 72 h prior to shift end (sleep versus need, SVN72). Across the study period, the drivers’ sleep was close to their self-reported sleep need, but 45% of the drivers showed accumulated sleep loss of >6 h at least once. SVN72 averaged −1.5 h and was 2.87 h shorter in connection with morning shifts compared to day or evening shifts. Night shifts showed no such difference. During days off, sleep exceeded sleep need by 1.13 h and was not dependent on the type of preceding work shift. SVN72 showed small-to-medium negative associations with on-duty KSS even after accounting for sleep within the 24 h prior to the shift end. Our results show that long-haul truck drivers are exposed to severe levels of accumulated sleep loss while working irregular shifts, but they can catch up on their lost sleep, especially during days off.

The effect of 60-h sleep deprivation (SD) on physical performance and motor control was studied. Twenty cadets were measured for aerobic performance (VO2) before and immediately after the SD period. Maximal strength and EMG of the knee extensor muscles were measured before and after 60 h of SD. Balance, reaction times and motor control were assessed every evening and morning during the SD period. Main effects were observed for heart rate (p = 0.002, partial eta squared: 0.669), VO2 (p = 0.004, partial eta squared: 0.621), ventilation (p = 0.016, partial eta squared: 0.049), and lactate concentration (p = 0.022, partial eta squared: 0.501), whereas RER remained unaltered (p = 0.213, partial eta squared: 0.166). Pairwise comparisons revealed decreased values at submaximal loads in heart rate, VO2, ventilation (all p < 0.05) but not in RER, whereas all of their respective maximal values remained unchanged. Moreover, pairwise comparisons revealed decreased lactate concentration at maximal performance but only at 8-min time point during submaximal workloads (p < 0.05). Pairwise comparisons of maximal strength, EMG and rate of force development revealed no change after SD. Main effects were observed for motor and postural control, as well as for reaction times (all p < 0.05), whereas pairwise comparison did not reveal a consistent pattern of change. In conclusion, motor control can mostly be maintained during 60-h SD, and maximal neuromuscular and aerobic performances are unaffected. However, submaximal cardiorespiratory responses seem to be attenuated after SD. peerReviewed