Evening physical activity alters wrist temperature circadian rhythmicity

The adequate time to perform physical activity (PA) to maintain optimal circadian system health has not been defined. We studied the influence of morning and evening PA on circadian rhythmicity in 16 women with wrist temperature (WT). Participants performed controlled PA (45?min continuous-running) during 7 days in the morning (MPA) and evening (EPA) and results were compared with a no-exercise-week (C). EPA was characterized by a lower amplitude (evening: 0.028?±?0.01?°C versus control: 0.038?±?0.016?°C; p?<?0.05) less pronounced second-harmonic (power) (evening: 0.41?±?0.47 versus morning: 1.04?±?0.59); and achrophase delay (evening: 06:35?±?02:14?h versus morning: 04:51?±?01:11?h; p?<?0.05) as compared to MPA and C. Performing PA in the late evening might not be as beneficial as in the morning.     

Diurnal rhythms of body temperature, heart rate, and behaviour in the stanchioned adult Shiba goats

Using a data logger system, body temperature (dorsal subcutaneous temperature), heart rate, ingestive or ruminating behaviour and posture in adult Shiba goats tied to a stanchion were recorded automatically during 24 hours, to obtain basic information on the biological rhythms. A 600 g of usual ration mixed with hay cube, hay, beet pulp and wheat bran was fed twice a day (morning; 9:00-9:30, evening; 16:00-16:30). Animals kept under an artificial photoperiod (12L-12D, light period; 5:30-17:30) and about 10 degrees C room temperature. 1) Diurnal patterns of the above-mentioned items were recorded, mutual relationships relationships between these items were revealed. 2) The heart rate was higher after morning feeding, or during a light period and decreased gradually from midnight to early morning. Twice feeding greatly increased the heart rate. 3) The body temperature was lower in the early morning and increased gradually after morning feeding and showed the highest level during 1 to 1.5 hours after evening feeding. After that it decreased gradually till the early morning. 4) The numbers of jaw movement (bites/min) were a 70-90 bites in the ingestive behaviour and a 80-90 bites in the ruminating behaviour at dark period. 5) The total heart rate was a 110000 to 120000 beats/day, the total biting time was a 9.5 hours/day, and the mean standing time was a 9.3 to 11.7 hours/day. The standing time during light period (12 hours) was a 7.3 to 9.9 hours and that during dark period (12 hours) was a 1.8 to 2 hours.     

Circadian variations in the sweating mechanism.

Sweat rates and body temperatures of human subjects were measured at 0200, 1000, and 1800 h during a heat exposure of 90 min. The latent period of sweating was not significantly altered in the evening but significantly shortened during the night. Mean body temperature corresponding to the onset of sweating was nearer to the basal body temperature during the night, while during the day the difference between these two temperatures became larger. This phenomenon seems related to the circadian cycle of vasomotor adjustment, since during the night body conductance was higher than during the day and corresponded to a state of a vasodilatation similar to that observed at the onset of sweating. During the day, this situation was reversed. During steady state, the following changes were observed: sweating rate, night less than morning less than evening; skin temperatures, night less than morning less than evening; and rectal temperature increase, morning less than evening less than night. It is hypothesized that these changes are due to either different metabolic rates or an imbalance between heat gains and losses which preserve the circadian rhythm of the body temperature, even under thermal loads.     

Evening rather than morning increased physical activity alters the microbiota in mice and is associated with increased body temperature and sympathetic nervous system activation

Voluntary training and food modulate the fecal microbiota in humans and mice. Although there are some reports of the timing effects of voluntary training and feeding on metabolism, the timing effects of these factors on microbiota have not been investigated. Therefore, we investigated the effects of the timing of voluntary training and feeding on the gut microbiota.The ICR mice were housed under conditions with an early (in the morning) or late (evening) active phase of increased physical activity. Furthermore, to investigate why voluntary training affects the gut microbiota, mice were housed in a cold environment and received propranolol administration with increased physical activity. After that, we collected cecal contents and feces and measured cecal pH. Short-chain fatty acids (SCFA) were measured from cecal contents. Microbiota was determined using sequencing of the V3-V4 region of the 16S rDNA gene.This study found that increased evening physical activity rather than morning activity decreases cecal pH, increases SCFA, and changes the microbiota. It is especially important that increased evening physical activity is induced under the post-prandial voluntary training condition. Also, we found that cold room housing, sympathetic blockade, or both suppressed the increased physical activity-induced changes in cecal pH, SCFA, and microbiota. Allobaculum responded to increased physical activity through body temperature increases and sympathetic activation.Post-prandial increased physical activity, rather than pre-prandial increased physical activity by evening voluntary wheel training, altered the microbiota composition, which may be related to the increase in body temperature and sympathetic nervous system activation.     

Chronotype and postmenopausal breast cancer risk among women in the California Teachers Study

ABSTRACT

Chronotype is the behavioral manifestation of an individual’s underlying circadian rhythm, generally characterized by one’s propensity to sleep at a particular time during the 24 hour cycle. Evening chronotypes (“night owls”) generally suffer from worse physical and mental health compared to morning chronotypes (“morning larks”) – for reasons that have yet to be explained. One hypothesis is that evening chronotypes may be more susceptible to circadian disruption, a condition where the coordinated timing of biologic processes breaks down. The role of chronotype as an independent or modifying risk factor for cancer has not been widely explored. The objective of the current study was to evaluate the risk of breast cancer associated with chronotype in a case-control study nested within the California Teachers Study (CTS) cohort. The study population consisted of 39686 post-menopausal CTS participants who provided information on chronotype by completing a questionnaire in 2012–2013. 2719 cases of primary invasive breast cancer diagnosed from 1995/1996 through completion of the chronotype questionnaire were identified by linkage of the CTS to the California Cancer Registry. 36967 CTS participants who had remained cancer-free during this same time period served as controls. Chronotype was ascertained by responses to an abbreviated version of the Horne-Ostberg Morningness-Eveningness Questionnaire (MEQ) and was characterized into five categories: definite morning, more morning than evening, neither morning or evening, more evening than morning, definite evening. Multivariable unconditional logistic regression analyses were performed to estimate the odds ratios (ORs) and 95% confidence intervals (95% CIs) for each of the chronotypes, adjusted for established breast cancer risk factors. Compared to definite morning types, definite evening types had an increased risk of breast cancer with elevated ORs that were statistically significant in both the crude (OR = 1.24, 95% CI: 1.10–1.40) and fully-adjusted models (OR = 1.20, 95% CI: 1.06–1.35). The risk estimates in the fully-adjusted model for all other chronotypes did not significantly differ from one. These results suggest that evening chronotype may be an independent risk factor for breast cancer among a population of women who are not known to have engaged in any substantial night shift work. Further research in other populations of non-shift workers is warranted.     

Day length and evening temperature predict circannual variation in activity duration of the colony of the Indian cliff swallow,Hirundo fluvicola

In avian species, circannual rhythms, in a number of biological variables, including locomotor activity, have been studied under both laboratory and natural environmental conditions. However, information on circannual rhythm in daily activity duration of Indian cliff swallow (Hirundo fluvicola) is not available. It is a communal mud nesting, non-migratory species and inhabits low under arch bridges. Although it figures in the IUCN Red List under the least concerned category, it is important to study its behavioral ecology that may be of utmost importance from conservation stand point. In the present investigation, we examined the circannual rhythm in daily activity duration in this species at a communal roosting site under Kharoon river bridge on the Raipur–Bhilai highway (21°15′07.54′′N; 81°32′30.65′′E), Raipur, India, for eight consecutive days, every month from August 2009 to October 2011. On each study day, observations were made in two sessions, morning and evening. We monitored and recorded emergence time of the first bird from the nest in the morning and entry time of the last bird to the nest in the evening. We also recorded the ambient temperature and humidity of the study site simultaneously. Average daily activity duration (the time difference between the first bird’s emergence time and the last bird’s entry time from/to the nest, respectively) was computed for each month. A significant circannual rhythm in activity duration was validated. The peak of activity rhythm occurred on 22nd June with a spread between 19th June and 25th June. The activity duration was the shortest in winter and the longest in summer. The daily activity duration was positively correlated to the day length, sunset time, and morning and evening temperatures; whereas negatively correlated with the sunrise time, and morning and evening humidity. The multiple linear regression models suggest that day length alone explains 96% of the total variance in activity duration, whereas only 0.5% variance was attributable to evening temperature. We conclude that the day length is the strongest predictor of circannual variation in daily activity duration of the colony of Indian cliff swallow; whereas the evening temperature has very little effect. Further, we recommend that comparable studies under natural conditions might be very helpful to explore the effect of environmental cues on other intriguing behavioral decisions made by this and other avian species.     

Thermal comfort conditions in the morning and in the evening

Eight females and eight males participated each in 4 comfort experiments on 4 different days. Two experiments took place in the morning and two in the evening. In each experiment (21/2 hours) the preferred ambient temperature was determined for each subject by adjusting the ambient temperature according to his wishes. The subjects were sedentary. Skin temperatures, rectal temperature and evaporative weight loss were measured. Although the rectal temperature and the mean skin temperature were slightly higher in the evening than in the morning the subjects did not prefer an ambient temperature which was different from that in the morning. This indicates that the same thermal comfort conditions can be used from morning to evening.     

Morning versus evening dosing of desloratadine in seasonal allergic rhinitis: a randomized controlled study [ISRCTN23032971].

BACKGROUND: A circadian rhythm of symptoms has been reported in allergic rhinitis and some studies have shown the dosing time of antihistamines to be of importance for optimizing symptom relief in this disease. The objective of this study was to examine the efficacy of morning vs. evening dosing of the antihistamine desloratadine at different time points during the day. METHODS: Patients >/= 18 years, with seasonal allergic rhinitis received desloratadine 5 mg orally once daily in the morning (AM-group) or evening (PM-group) for two weeks. Rhinorrhea, nasal congestion, sneezing and eye symptoms were scored morning and evening. Wilcoxon rank sum and 2-way ANOVA test were used. RESULTS: Six-hundred and sixty-three patients were randomized; 336 in the AM-group; 327 in the PM-group. No statistically significant differences were seen between the AM and PM group at any time points. In the sub-groups with higher morning or evening total symptom score no difference in treatment efficacy was seen whether the dose was taken 12 or 24 hours before the higher score time. There was a circadian variation in baseline total symptom score; highest during daytime and lowest at night. The circadian variation in symptoms was reduced during treatment. This reduction was highest for daytime symptoms. CONCLUSIONS: A circadian rhythm was seen for most symptoms being more pronounced during daytime. This was less apparent after treatment with desloratadine. No statistically significant difference in efficacy was seen whether desloratadine was given in the morning or in the evening. This gives the patients more flexibility in choosing dosing time.     

A 30-year study of body temperature variations correlated with menstrual cycle,seasonality, and aging

Studies of human body temperature typically involve a small number of subjects or measurements taken over a relatively short timeframe. To enhance the size of the data-set and more reliably distinguish outlying values, oral temperature was measured each evening in a single female subject for 30 years. The results confirmed the well-known temperature variations during the menstrual cycle and the decreased temperature in older adults compared to young adults. The present study’s large data-set extended these results, revealing a gradual decline in temperature with advancing age during middle-age and a rapid decline in temperature during menopause. The results also revealed a convincing seasonal variation in body temperature that peaked in August and were lowest in February–March. A modest shift in body temperature was also related to daylight-saving time change. These results confirm and extend the findings of earlier studies, showing the relationship of body temperature to the menstrual cycle, seasonality, and aging.     

The association between sleep chronotype and obesity among black and white participants of the Bogalusa Heart Study

ABSTRACT

Research indicates that sleep duration and quality are inter-related factors that contribute to obesity, but few studies have focused on sleep chronotype, representing an individual’s circadian proclivity, nor assessed these factors in racially diverse middle-aged samples. We examined the associations between chronotype and obesity among black and white men and women participating in the Bogalusa Heart Study (BHS).

Body mass index (BMI) and sleep data were available for 1,197 middle-aged men and women (mean age 48.2 ± 5.3 years) who participated in the BHS 2013–2016. Based on the reduced Morningness-Eveningness Questionnaire’s cutoff values for chronotypes, we combined ‘definitely morning’ and ‘moderately morning’ types into ‘morning’ type, ‘definitely evening’ and ‘moderately evening’ types into ‘evening’ type and kept those who were “neither” type in a separate group. We used ‘morning’ type as the referent group. Obesity was defined as a BMI ≥ 30. Multivariable logistic regression models were used to examine associations adjusting for sex, age, education, smoking, alcohol use and drug use, depression, shift work, physical activity and sleep duration.

Evening chronotype, reported by 11.1% of participants, was associated with obesity after multi-variable adjustment, including shift work, physical activity and sleep duration (OR 1.67, 95% CI: 1.08–2.56). However, once stratified by race (black/white), this association was found only among white participants (OR = 1.91, 95% CI = 1.12–3.25) after full adjustment.

In our biracial, community-based population, evening chronotype was independently associated with obesity, specifically among white participants. Further research is needed to identify behavioral, endocrine, nutritional and genetic pathways which underlie these associations.     

Temperature profiles, and the effect of sleep on them, in relation to morningness-eveningness in healthy female subjects

There were 15 healthy female subjects, differing in their position on the “morningness-eveningness” scale, studied for 7 consecutive days, first while living a sedentary lifestyle and sleeping between midnight and 08:00 and then while undergoing a “constant routine.” Rectal temperature was measured at regular intervals throughout this time, and the results were subjected to cosinor analysis both before and after “purification” for the effects of physical activity. Results showed that there was a phase difference in the circadian rhythm of core temperature that was associated with the morningness score, with calculations that “morning types” would be phased earlier than “evening types” by up to about 3h. This difference in phase (which was also statistically significant when the group was divided by a median split into a “morning group” and an “evening group”) could not be attributed to effects of waking activity and existed in spite of the subjects keeping the same sleep-wake schedule. Moreover, it persisted when the subjects' data had been purified and when the data were obtained from the constant routine. That is, there was an endogenous component to this difference in phase of the core temperature. The morning group also showed a greater fall of core temperature during sleep; this was assessed in two ways, the main one being a comparison of constant routine and nychthemeral data sets after correction for any effects of activity. Even though the morning group was sleeping at a later phase of their circadian temperature rhythm than was the evening group, neither group showed a fall of temperature due to sleep that varied with time elapsed since the temperature acrophase. It is concluded that another factor that differs between morning and evening types is responsible for this difference. (Chronobiology International, 18(2), 227-247, 2001)     

Thermal ecology of the smooth snake,Coronella austriaca Laurenti,during spring

Summary Thermo sensitive transmitters were used in a study on free-ranging smooth snakes (Coronella austriaca). Except on cold cloudy days, this snake shows a daily tripartite pattern of body temperatures. The pattern consists of a quick rise in body temperature in the morning, a subsequent stable phase during which body temperatures vary between 29 and 33° C, and finally a drop of body temperatures in the evening. The, consistency of the stable phase over the study period indicates that this range represents the thermal preferendum of this species. During the succesive study months a time shift in daily activity pattern was observed.     

Effect of the time of day on central and peripheral fatigue during 2-min maximal voluntary contractions in persons with multiple sclerosis: gender differences

There is a lack of data on fatigue changes within 24 h among patients with multiple sclerosis. The purpose of this study was to evaluate the effect of time of day on central and peripheral fatigue during a continuous 2-min maximal voluntary contraction of the quadriceps muscle in women and men with multiple sclerosis (MS). We studied age-matched MS patients (range, 40–50 years). The inclusion criteria for patients were: a Kurtzke Expanded Disability Status score and a Fatigue Severity Scale score. We found a significant gender difference in central activation ratio (CAR) in the evening. At the end of the 2-min maximal voluntary contraction (MVC), the voluntary torque decreased by about 65% in men and women with MS in both the morning and evening. We also observed that, in women, CAR decreased markedly during the first 30 s in the evening test. The most interesting finding of our study is that central fatigue increased, whereas peripheral fatigue decreased markedly in the evening only in women. It remains unclear why women’s central fatigue is greater in the evening than in the morning.     

Combination of meal and exercise timing with a high-fat diet influences energy expenditure and obesity in mice

In mice, obesity has been observed not only in those freely fed a high-fat diet (HFD) but also in those fed while physically inactive. In contrast, a HFD during physically active periods protects against obesity and the impairments in the circadian rhythm induced by free feeding of a HFD. Although exercise is known to be effective for obesity prevention and management, the optimal timing of exercise has not yet been determined. In the present experiments, we aimed to determine the best combination of daily timing of HFD consumption and exercise for the prevention of HFD-induced weight gain in mice. In this experiment, “morning” refers to the beginning of the active phase (the “morning” for nocturnal animals). Increases in body weight related to free feeding of a HFD was significantly reduced with 4?h of exercise during the late (evening) or middle (noon) active period compared to 4?h of exercise during the early (morning) active period or free access to exercise, which resulted in hours of exercise similar to that of morning exercise. These results suggested that eating in the morning or at noon followed by exercise in the evening could prevent weight gain more effectively than exercise in the morning followed by eating at noon or in the evening. The group fed a HFD for 4?h in the morning had lower body weight than the group fed a HFD for 4?h in the evening without exercise. The last group of experiments tested the hypothesis that there would be an interaction between mealtime and exercise time (i.e. time of day) versus order (i.e. which comes first) effects. We compared groups that exercised for 4?h at noon and were fed either in the morning or evening and groups that were fed for 4?h at noon and either exercised in the morning or evening. We found that the groups that were fed before exercise gained less body and fat weight and more skeletal muscle weight compared to the groups that exercised before eating. Corresponding to the body and fat weight changes, the respiratory exchange ratio (RER) was lower and energy expenditure was higher in the groups fed before exercise than in the groups fed after exercise, and these effects on energy metabolism were also observed in the early stage of HFD feeding before obesity. When obese mice fed a HFD for 12 weeks were exposed to a combination of feeding and exercise timing in an effort to reduce body weight, eating followed by exercise resulted in greater weight loss, similar to the experiments conducted to prevent weight gain. These results demonstrate that a combination of daily timing of eating and exercise may influence weight gain and that eating followed by exercise may be effective for minimizing increases in body and fat weight as well as maximizing increases in skeletal muscle weight.     

TEMPERATURE PROFILES,AND THE EFFECT OF SLEEP ON THEM,IN RELATION TO MORNINGNESS-EVENINGNESS IN HEALTHY FEMALE SUBJECTS

There were 15 healthy female subjects, differing in their position on the “morningness-eveningness” scale, studied for 7 consecutive days, first while living a sedentary lifestyle and sleeping between midnight and 08:00 and then while undergoing a “constant routine.” Rectal temperature was measured at regular intervals throughout this time, and the results were subjected to cosinor analysis both before and after “purification” for the effects of physical activity. Results showed that there was a phase difference in the circadian rhythm of core temperature that was associated with the morningness score, with calculations that “morning types” would be phased earlier than “evening types” by up to about 3h. This difference in phase (which was also statistically significant when the group was divided by a median split into a “morning group” and an “evening group”) could not be attributed to effects of waking activity and existed in spite of the subjects keeping the same sleep-wake schedule. Moreover, it persisted when the subjects' data had been purified and when the data were obtained from the constant routine. That is, there was an endogenous component to this difference in phase of the core temperature. The morning group also showed a greater fall of core temperature during sleep; this was assessed in two ways, the main one being a comparison of constant routine and nychthemeral data sets after correction for any effects of activity. Even though the morning group was sleeping at a later phase of their circadian temperature rhythm than was the evening group, neither group showed a fall of temperature due to sleep that varied with time elapsed since the temperature acrophase. It is concluded that another factor that differs between morning and evening types is responsible for this difference. (Chronobiology International, 18(2), 227–247, 2001)     

Day and Night Aspirin-Induced Gastric Mucosal Damage and Protection by Ranitidine in Man

The severity of gastric mucosal injury produced by aspirin (ASA) was endoscopically assessed during morning and evening studies in 10 healthy, male volunteers. In a randomized, double-blind design, subjects received either ASA (1300 mg) alone or ASA (1300 nig) plus Ranitidine (150mg) or placebo tablets during morning and evening studies. Each subject had 3 morning and 3 evening studies. The severity of damage produced by ASA was assessed by counting the number of punctate mucosal hemorrhages observed in the gastric antrum and low-body. This study demonstrated (1) wide intersubject variability in the severity of damage produced by ASA (range of 47-1030 lesions/subject in morning studies), (2) significant protection against ASA-indueed damage by Ranitidine and (3) significantly greater damage produced by ASA in the morning compared to the evening studies. Because evening acid secretory rates are higher and because ASA-induced damage is believed to be acid-dependent, this last observation was unexpected. It suggests mucosal resistance is higher in the evening and raises the possibility that there may be circadian variation in gastric mucosal resistance.     

Day and Night Aspirin-Induced Gastric Mucosal Damage and Protection by Ranitidine in Man

The severity of gastric mucosal injury produced by aspirin (ASA) was endoscopically assessed during morning and evening studies in 10 healthy, male volunteers. In a randomized, double-blind design, subjects received either ASA (1300 mg) alone or ASA (1300 nig) plus Ranitidine (150mg) or placebo tablets during morning and evening studies. Each subject had 3 morning and 3 evening studies. The severity of damage produced by ASA was assessed by counting the number of punctate mucosal hemorrhages observed in the gastric antrum and low-body. This study demonstrated (1) wide intersubject variability in the severity of damage produced by ASA (range of 47-1030 lesions/subject in morning studies), (2) significant protection against ASA-indueed damage by Ranitidine and (3) significantly greater damage produced by ASA in the morning compared to the evening studies. Because evening acid secretory rates are higher and because ASA-induced damage is believed to be acid-dependent, this last observation was unexpected. It suggests mucosal resistance is higher in the evening and raises the possibility that there may be circadian variation in gastric mucosal resistance.     

Time course of neurobehavioral alertness during extended wakefulness in morning- and evening-type healthy sleepers

The aim of the study was to evaluate the influence of chronotype (morning-type versus evening-type) living in a fixed sleep-wake schedule different from one's preferred sleep schedules on the time course of neurobehavioral performance during controlled extended wakefulness. The authors studied 9 morning-type and 9 evening-type healthy male subjects (21.4 ± 1.9 yrs). Before the experiment, all participants underwent a fixed sleep-wake schedule mimicking a regular working day (bedtime: 23:30 h; wake time: 07:30 h). Then, following two nights in the laboratory, both chronotypes underwent a 36-h constant routine, performing a cognitive test of sustained attention every hour. Core body temperature, salivary melatonin secretion, objective alertness (maintenance of wakefulness test), and subjective sleepiness (visual analog scale) were also assessed. Evening-types expressed a higher level of subjective sleepiness than morning types, whereas their objective levels of alertness were not different. Cognitive performance in the lapse domain remained stable during the normal waking day and then declined during the biological night, with a similar time course for both chronotypes. Evening types maintained optimal alertness (i.e., 10% fastest reaction time) throughout the night, whereas morning types did not. For both chronotypes, the circadian performance profile was correlated with the circadian subjective somnolence profile and was slightly phase-delayed with melatonin secretion. Circadian performance was less correlated with circadian core body temperature. Lapse domain was phase-delayed with body temperature (2-4 h), whereas optimal alertness was slightly phase-delayed with body temperature (1 h). These results indicate evening types living in a fixed sleep-wake schedule mimicking a regular working day (different from their preferred sleep schedules) express higher subjective sleepiness but can maintain the same level of objective alertness during a normal waking day as morning types. Furthermore, evening types were found to maintain optimal alertness throughout their nighttime, whereas morning types could not. The authors suggest that evening-type subjects have a higher voluntary engagement of wake-maintenance mechanisms during extended wakefulness due to adaptation of their sleep-wake schedule to social constraints.     

Evening typology and morning tiredness associates with low leisure time physical activity and high sitting

Circadian typology is a latent trait that is usually assessed with scoring on a series of questions thought to represent the construct. But, in the classification, most people fall into the intermediate type, i.e. neither a definite morning nor an evening type, but still showing stronger preference towards either end of the continuum. Our aim was to operationalize chronotype using latent class analysis (LCA) for a 6-item scale derived from the original Horne–Östberg Morningness–Eveningness Questionnaire to compare and understand characteristics of chronotype in a population-based sample of adults in Finland. A total of 4904 men and women aged 25–74 years were included. We also analyzed the associations of chronotypes with physical activity (PA) and sitting. We found five latent chronotype groups including “rested more-evening type” (28%), “rested more-morning type” (24%), “morning type” (23%), “tired more-evening type” (17%) and “evening type” (8%) groups. Operationalization of chronotype by LCA suggests that morning alertness is an important feature differentiating chronotypes. Further, the “evening type” and the “tired, more-evening type” had higher odds for none to very low as well as low PA, as compared to “morning type”. In addition, “evening type” was associated with higher odds for more time spent sitting, as compared to “morning type”. Our findings indicate that it is important to assess sleep schedules and morning tiredness, which then could be targeted as a potential mediating factor for health behaviors, in particular, PA and health status.     

Time Course of Neurobehavioral Alertness During Extended Wakefulness in Morning- and Evening-Type Healthy Sleepers

The aim of the study was to evaluate the influence of chronotype (morning-type versus evening-type) living in a fixed sleep-wake schedule different from one's preferred sleep schedules on the time course of neurobehavioral performance during controlled extended wakefulness. The authors studied 9 morning-type and 9 evening-type healthy male subjects (21.4?±?1.9 yrs). Before the experiment, all participants underwent a fixed sleep-wake schedule mimicking a regular working day (bedtime: 23:30?h; wake time: 07:30?h). Then, following two nights in the laboratory, both chronotypes underwent a 36-h constant routine, performing a cognitive test of sustained attention every hour. Core body temperature, salivary melatonin secretion, objective alertness (maintenance of wakefulness test), and subjective sleepiness (visual analog scale) were also assessed. Evening-types expressed a higher level of subjective sleepiness than morning types, whereas their objective levels of alertness were not different. Cognitive performance in the lapse domain remained stable during the normal waking day and then declined during the biological night, with a similar time course for both chronotypes. Evening types maintained optimal alertness (i.e., 10% fastest reaction time) throughout the night, whereas morning types did not. For both chronotypes, the circadian performance profile was correlated with the circadian subjective somnolence profile and was slightly phase-delayed with melatonin secretion. Circadian performance was less correlated with circadian core body temperature. Lapse domain was phase-delayed with body temperature (2–4?h), whereas optimal alertness was slightly phase-delayed with body temperature (1?h). These results indicate evening types living in a fixed sleep-wake schedule mimicking a regular working day (different from their preferred sleep schedules) express higher subjective sleepiness but can maintain the same level of objective alertness during a normal waking day as morning types. Furthermore, evening types were found to maintain optimal alertness throughout their nighttime, whereas morning types could not. The authors suggest that evening-type subjects have a higher voluntary engagement of wake-maintenance mechanisms during extended wakefulness due to adaptation of their sleep-wake schedule to social constraints. (Author correspondence: jack.taillard@gmail.com)