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Sleep-wake behavior, as well as sleepiness, is regulated by the joint action of an exponentially increasing drive for sleep--sleep homeostasis--and by variations in sleep propensity due to a biological circadian oscillator. However, large inter-individual differences remain. Short and long sleepers have been known to differ in the amount of homeostatic sleep pressure: long sleepers report higher levels of subjective sleepiness after sleep deprivation, whereas short sleepers exhibit no significant increase in sleepiness. The circadian pacemaker's program might be at the origin of the variability in habitual sleep duration in long and short sleepers. Previous studies within our group showed that the dynamics of both processes are similar in experienced sleepiness as in judged sleepiness. The aim of the present investigation was to determine whether habitual short, long and midrange sleepers exhibit similar integration patterns or whether the biological underpinnings of habitual sleep time variability emerge when judging sleepiness. Our results show an additive integration rule for homeostatic and circadian determinants of daytime sleepiness in all groups. However, rescaled functional values (RSFVs) and relative range indices (RRIs) suggest that short sleepers seem to tolerate higher levels of homeostatic sleep pressure in comparison to long sleepers and that in long sleepers, circadian variability plays a less prominent role in functional daytime sleepiness. As sleep-wake behavior is governed by both physiological mechanisms and psychological processes influenced by past experiences related to sleep and wake, these results have implications for sleep-wake-related health and safety. (Contains 5 figures, 5 tables, and 2 footnotes.)

Introduction: In 2018, the Belgian Defence introduced a commercial off-the-shelf dive computer (Shearwater Perdix™) for use by its military divers. There were operational constraints when using its default gradient factors (GF). We aimed to provide guidelines for optimal GF selection. Methods: The Defence and Civil Institute of Environmental Medicine (DCIEM) dive tables and the United States Navy (USN) air decompression tables are considered acceptably safe by the Belgian Navy Diving Unit. The decompression model used in the Shearwater Perdix (Bühlmann ZH-L16C algorithm with GF) was programmed in Python. Using a sequential search of the parameter space, the GF settings were optimised to produce decompression schedules as close as possible to those prescribed by the USN and DCIEM tables. Results: All reference profiles are approached when GFLO is kept equal to 100 and only GFHI is reduced to a minimum of 75 to prolong shallower stop times. Using the Perdix default settings (GFLO = 30 and GFHI = 70) yields deeper initial stops, leading to increased supersaturation of the 'slower' tissues, which potentially leads to an increased DCS risk. However, Perdix software does not currently allow for the selection of our calculated optimal settings (by convention GFLO < GFHI). A sub-optimal solution would be a symmetrical GF setting between 75/75 and 95/95. Conclusions: For non-repetitive air dives, the optimal GF setting is GFLO 100, with only the GFHI parameter lowered to increase safety. No evidence was found that using the default GF setting (30/70) would lead to a safer decompression for air dives as deep as 60 metres of seawater; rather the opposite. Belgian Navy divers have been advised against using the default GF settings of the Shearwater Perdix dive computer and instead adopt symmetrical GF settings which is currently the optimal achievable approach considering the software constraints. [ABSTRACT FROM AUTHOR]

Purpose: The 2-bout exercise protocol has been developed to diagnose nonfunctional overreaching and the "overtraining syndrome." It consists of 2 maximal exercise bouts separated by 4 hours. Mental fatigue negatively influences performance, but the effects of its occurrence during the 2-bout exercise protocol have never been investigated. The aim of this study was to examine whether mental fatigue (induced during the rest period) influences physical and cognitive performance during/after the second exercise bout of the 2-bout exercise protocol. Methods: Nine healthy, well-trained male cyclists participated in a singleblind, randomized, placebo-controlled crossover study. The intervention consisted of either 1.5-hour rest (control) or performing a computer-based Stroop task to induce mental fatigue. Cognitive (Eriksen Flanker task), physiological (lactate, maximum heart rate, and maximum wattage), and subjective data (mental fatigue-visual analog scale, Profile of Mood States, and rating of perceived exertion) were gathered. Results: Ratings of fatigue, tension, and mental fatigue were affected in the mental fatigue condition (P < .05). Neither physiological nor cognitive differences were found between conditions. Ratings of mental fatigue were already affected after the first maximum exercise test (P < .05). Conclusions: Neither physical nor cognitive performance was affected by mental fatigue, but subjective ratings did reveal significant differences. It is recommended to exclude mentally challenging tasks during the 2-bout exercise protocol rest period to ascertain unaffected subjective test results. This study should be repeated in athletes diagnosed with nonfunctional overreaching/overtraining syndrome. [ABSTRACT FROM AUTHOR]