Subjective and Objective Responses to Two Rugby Sevens World Series Competitions.

Fowler, PM, Murray, A, Farooq, A, Lumley, N, and Taylor, L. Subjective and objective responses to two rugby sevens world series competitions. J Strength Cond Res 33(4): 1043-1055, 2019-The purpose was to examine the utility of subjective and objective measures of player preparedness, interpreted at both group level and individual level, during 2 consecutive competitions of the World Rugby Sevens Series (WRSS). Subjective (sleep, energy, and muscle soreness ratings) and objective (heart rate [HR] at rest [HRREST] and in response to submaximal exercise [HREX]) measures were obtained from 16 male rugby 7s players from 1 team for 3 consecutive days (D1-3) at home (HOME) and on arrival at 4 tournament (T1-4) locations (T1-New Zealand; T2-USA; T3-Hong Kong; and T4-Tokyo) across 2 WRSS competitions (2 tournaments per competition) separated by 1 month. At a group level, energy ratings were significantly lower in T2 and T4 compared with HOME, and on D1 T2 compared with D1 T1 (p ≤ 0.05). Greatest variability in subjective ratings was observed during T1 and T3 at an individual level, particularly for sleep quality. Although at a group level HRREST and HREX significantly decreased in T1-4 compared with HOME (p ≤ 0.05), there was only a ∼50% agreement between the direction of change in HR indices at an individual level. Results from this study suggest that relocation between tournaments within WRSS competitions disrupts player preparedness measures to the largest degree. Hence, this period could be targeted by practitioners with appropriate recovery and/or sleep-promoting interventions or modulation of match-/training-load. Moreover, subjective rather than objective measures seem to be of greater use to inform player preparedness decision making, particularly at an individual level compared with a group level.

Light and the human circadian clock.

The circadian clock can only reliably fulfil its function if it is stably entrained. Most clocks use the light-dark cycle as environmental signal (zeitgeber) for this active synchronisation. How we think about clock function and entrainment has been strongly influenced by the early concepts of the field's pioneers, and the astonishing finding that circadian rhythms continue a self-sustained oscillation in constant conditions has become central to our understanding of entrainment.Here, we argue that we have to rethink these initial circadian dogmas to fully understand the circadian programme and how it entrains. Light is also the prominent zeitgeber for the human clock, as has been shown experimentally in the laboratory and in large-scale epidemiological studies in real life, and we hypothesise that social zeitgebers act through light entrainment via behavioural feedback loops (zeitnehmer). We show that human entrainment can be investigated in detail outside of the laboratory, by using the many 'experimental' conditions provided by the real world, such as daylight savings time, the 'forced synchrony' imposed by the introduction of time zones, or the fact that humans increasingly create their own light environment. The conditions of human entrainment have changed drastically over the past 100 years and have led to an increasing discrepancy between biological and social time (social jetlag). The increasing evidence that social jetlag has detrimental consequences for health suggests that shift-work is only an extreme form of circadian misalignment, and that the majority of the population in the industrialised world suffers from a similarly 'forced synchrony'.

Effect of airline travel on performance: a review of the literature.

The need for athletes to travel long distances has spurred investigation into the effect of air travel across multiple time zones on athletic performance. Rapid eastward or westward travel may negatively affect the body in many ways; therefore, strategies should be employed to minimise these effects which may hamper athletic performance. In this review, the fundamentals of circadian rhythm disruption are examined along with additional effects of airline travel including jet lag, sleep deprivation, travel at altitude and nutritional considerations that negatively affect performance. Evidence-based recommendations are provided at the end of the manuscript to minimise the effects of airline travel on performance.

Human circadian variations.

Circadian rhythms, present in most phyla across life, are biological oscillations occurring on a daily cycle. Since the discovery of their molecular foundations in model organisms, many inputs that modify this tightly controlled system in humans have been identified. Polygenic variations and environmental factors influence each person's circadian rhythm, contributing to the trait known as chronotype, which manifests as the degree of morning or evening preference in an individual. Despite normal variation in chronotype, much of society operates on a "one size fits all" schedule that can be difficult to adjust to, especially for certain individuals whose endogenous circadian phase is extremely advanced or delayed. This is a public health concern, as phase misalignment in humans is associated with a number of adverse health outcomes. Additionally, modern technology (such as electric lights and computer, tablet, and phone screens that emit blue light) and lifestyles (such as shift or irregular work schedules) are disrupting circadian consistency in an increasing number of people. Though medical and lifestyle interventions can alleviate some of these issues, growing research on endogenous circadian variability and sensitivity suggests that broader social changes may be necessary to minimize the impact of circadian misalignment on health.

Modeling the circadian clock: from molecular mechanism to physiological disorders.

Based on genetic and biochemical advances on the molecular mechanism of circadian rhythms, a computational model for the mammalian circadian clock is used to examine the dynamical bases of circadian-clock-related physiological disorders in humans. Entrainment by the light-dark cycle with a phase advance or a phase delay is associated with the Familial advanced sleep phase syndrome (FASPS) or the Delayed sleep phase syndrome (DSPS), respectively. Lack of entrainment corresponding to the occurrence of quasiperiodic oscillations with or without phase jump can be associated with the non-24 h sleep-wake syndrome. In the close vicinity of the entrainment domain, the model uncovers the possibility of infradian oscillations of very long period. Perturbation in the form of chronic jet lag, as used in mice, prevents entrainment of the circadian clock and results in chaotic or quasiperiodic oscillations. It is important to clarify the conditions for entrainment and for its failure because dysfunctions of the circadian clock may lead to physiological disorders, which pertain not only to the sleep-wake cycle but also to mood and cancer.

Different effects of heat exposure upon exercise performance in the morning and afternoon.

Independent of environmental conditions, rectal temperature follows a circadian rhythm with an acrophase in the late afternoon. In neutral environment, this diurnal increase in temperature is believed to have a passive warm-up effect improving muscle contractility, and in turn, muscle force, power and performance. However, a hot environment blunts the diurnal variation in muscle function by only improving muscle contractility, and in turn, muscle force, power and performance in the morning, when body temperature is at its lowest. Despite this diurnal variation in muscle function, long-duration exercise is only slightly affected by the time-of-day in neutral environment. However, higher afternoon body temperatures can reduce the heat storage capacity and result in a reduction in exercise capacity in hot environments. In addition, in parallel to the circadian variations in muscle contractility and central temperature, exercise capacity in hot environment may also be affected by the diurnal variations in melatonin concentration and in the onset of peripheral vasodilatation and sweating.

Afternoon School Start Times Are Associated with a Lack of Both Social Jetlag and Sleep Deprivation in Adolescents.

The delayed circadian timing of adolescents creates a conflict with early school start times (SSTs). We used wrist actimetry to compare sleep parameters and routine nighttime activities in middle school students attending either a morning (0700 to 1200 h) or an afternoon (1230 to 1730 h) school shift. On school days, students from both shifts (n = 21 for morning shift, n = 20 for afternoon shift, ages 12-14 years) had a similar sleep onset, but morning-shift students had an earlier sleep offset and a 1 h 45 min shorter sleep duration than their afternoon peers, who slept the recommended 8 to 10 h of daily sleep. Only morning-shift students had afternoon naps, but this afternoon sleep was not sufficient to overcome sleep deprivation. On weekends, sleep onsets and offsets did not differ between shifts. Because only morning-shift students woke up later and slept longer (2 h 3 min) on weekends, they were also the only ones who experienced social jetlag. Daily surveys on their nighttime (from 1800 to 0600 h) activities indicated there was no difference between shifts in the time spent on leisure or using electronic media during school days, but students from both shifts spent more time in these activities during the weekend. Our study confirms that early SST in adolescents is associated with sleep deprivation and suggests that schedules that start much later than typically considered may be needed to eliminate sleep deprivation in adolescents.

Effects of lockdown on human sleep and chronotype during the COVID-19 pandemic.

The COVID-19 pandemic [1] resulted in many countries imposing a lockdown, which in turn reduces sunlight exposure and alters daily social schedules. Since these are the main entrainment factors for biological rhythms [2], we hypothesized that the lockdown may have affected sleep and circadian rhythms. We indeed show that participants slept longer and later during lockdown weekdays, and exhibited lower levels of social jetlag. While this may seem to be an overall improvement of sleep conditions, chronotype was also delayed under the lockdown. This signature of a weaker light-dark cycle should be monitored attentively since it may progressively cause disruptive effects on sleep and circadian rhythms, affecting human performance and health [3].

Jet lag and other sleep disorders relevant to the traveler.

Sleep and wakefulness are governed by homeostatic and circadian regulatory processes, and perturbations therein are primarily responsible for the sleep disturbances associated with travel. Misalignment between endogenous rhythms and the light/dark cycle can result in circadian rhythm sleep disorders, including jet lag. This condition will be the primary focus of this review, with an emphasis on predisposing factors, preventative options, and treatment strategies.

Sunset time and the economic effects of social jetlag: evidence from US time zone borders.

The rapid evolution into a 24 h society challenges individuals' ability to conciliate work schedules and biological needs. Epidemiological research suggests that social and biological time are increasingly drifting apart ("social jetlag"). This study uses a spatial regression discontinuity design to estimate the economic cost of the misalignment between social and biological rhythms arising at the border of a time-zone in the presence of relatively rigid social schedules (e.g., work and school schedules). Exploiting the discontinuity in the timing of natural light at a time-zone boundary, we find that an extra hour of natural light in the evening reduces sleep duration by an average of 19 minutes and increases the likelihood of reporting insufficient sleep. Using data drawn from the Centers for Disease Control and Prevention and the US Census, we find that the discontinuity in the timing of natural light has significant effects on health outcomes typically associated with circadian rhythms disruptions (e.g., obesity, diabetes, cardiovascular diseases, and breast cancer) and economic performance (per capita income). We provide a lower bound estimate of the health care costs and productivity losses associated with these effects.

Are Individual Differences in Sleep and Circadian Timing Amplified by Use of Artificial Light Sources?

Within the human population, there is large interindividual variability in the timing of sleep and circadian rhythms. This variability has been attributed to individual differences in sleep physiology, circadian physiology, and/or light exposure. Recent experimental evidence suggests that the latter is necessary to evoke large interindividual differences in sleep and circadian timing. We used a validated model of human sleep and circadian physiology to test the hypothesis that intrinsic differences in sleep and circadian timing are amplified by self-selected use of artificial light sources. We tested the model under 2 conditions motivated by an experimental study (Wright et al., 2013): (1) a "natural" light cycle, and (2) a "realistic" light cycle that included attenuation of light due to living indoors when natural light levels are high and use of electric light when natural light levels are low. Within these conditions, we determined the relationship between intrinsic circadian period (within the range of 23.7-24.6 h) and timing of sleep onset, sleep offset, and circadian rhythms. In addition, we simulated a work week, with fixed wake time for 5 days and free sleep times on weekends. Under both conditions, a longer intrinsic period resulted in later sleep and circadian timing. Compared to the natural condition, the realistic condition evoked more than double the variation in sleep timing across the physiological range of intrinsic circadian periods. Model predictions closely matched data from the experimental study. We found that if the intrinsic circadian period was long (>24.2 h) under the realistic condition, there was significant mismatch in sleep timing between weekdays and weekends, which is known as social jetlag. These findings indicate that individual tendencies to have very delayed schedules can be greatly amplified by self-selected modifications to the natural light/dark cycle. This has important implications for therapeutic treatment of advanced or delayed sleep phase disorders.

Social jet-lag potentiates obesity and metabolic syndrome when combined with cafeteria diet in rats.

BACKGROUND/OBJECTIVES: Modern lifestyle promotes shifted sleep onset and shifted wake up time between weekdays and weekends, producing a condition termed "social-jet lag." Disrupted sleep promotes increased appetite for carbohydrate and fat-rich food, which in long term leads to overweight, obesity and metabolic syndrome. In order to mimic the human situation we produced an experimental model of social-jet lag (Sj-l). With this model, we explored the link between shifted sleep time with consumption of a cafeteria diet (CafD) and the development of obesity and metabolic syndrome. SUBJECTS/METHODS: The first experiment was designed to create and confirm the model of Sj-l. Rats (n=8-10/group) were exposed to a shifted sleep time protocol achieved by placing the rats in slow rotating wheels from Monday to Friday during the first 4h of the light period, while on weekends they were left undisturbed. The second experiment (n=8-12/group) explored the combined effect of Sj-l with the opportunity to ingest CafD. All protocols lasted 12weeks. We evaluated the development of overweight and indicators of metabolic syndrome. The statistical significance for all variables was set at P<0.05. RESULTS: Sj-l alone did not affect body weight gain but induced significant changes in cholesterol in metabolic variables representing a risk factor for metabolic syndrome. Daily restricted access to CafD in the day or night induced glucose intolerance and only CafD during the day led to overweight. Sj-l combined with CafD induced overconsumption of the diet, potentiated body weight gain (16%) and promoted 5 of the criteria for metabolic syndrome including high insulin and dislipidemia. CONCLUSION: Present data provide an experimental model of social-jet lag that combined with overconsumption of CafD, and maximized the development of obesity and metabolic syndrome. Importantly, access to CafD during the night did not lead to overweight nor metabolic syndrome.

[Rhythms, depressions and light]. / Rytmer, depresjoner og lys.

Many aspects of life in plants, animals and humans are controlled by light. Endogenous, so-called circadian rhythms in the body deviate from the exact 24-hour day and have typically a period of around 25.5 hours in man. Normally these rhythms adapt to the external 24-hour day-and night changes but under constant conditions the rhythms can free run. Many studies show how important the interplay between light and the circadian rhythms are for man as well as for other organisms. The control of these rhythms by light is mediated via the retina and the melatonin system in man. The adaptation of the rhythms is very important in shift work, in rapid jet lag travels over time zones, etc. Organisms often use the circadian rhythm to determine the length of day and of night, a feature that has given rise to the term biological clocks. A biological clock provides possibilities to determine the proper time for physiological processes to start in plants and animals (flowering, hibernation etc). The importance of light and circadian rhythms for seasonal affective disorders and manic-depressive disorders is also discussed. For several organisms one has now been able to specify genes that determine the period of the clocks. The rhythmic physiologic processes, the light reactions and the general importance of light for rhythms and for man are now studied at the molecular level.

Changes in melatonin secretion in tourists after rapid movement to another lighting zone without transition of time zone.

Most of the research in the field of Chronobiology is focused on the problem of the circadian rhythms (CR) desynchronization. In travelers, it results mostly from the changes of surrounding: photoperiod, local climate conditions (radiation and thermal load) and behavior (e.g. type and place of tourism and activity level). Until now, it was not documented whether the changes in melatonin (MLT) secretion occur in effect of mid-distance transparallel travels (TpT), without complications arising due to time-zone transitions (e.g. jet-lag syndrome). To cope with this problem, a special field experiment was carried out. In the experiment, MLT characteristics were examined twice a year in real conditions through a group of young tourists (23-26 years old) at their place of habitual residence (Warsaw, Poland), and at their tourist destination (Tromso, Norway). Transition to circumpolar zone in summer has resulted in insignificant reduction in melatonin peak value (MPV) compared to preflight control (2 days before travel) and the melatonin peak time (MPT) was delayed. However, after traveling southward on the returning flight, MPV was lower compared to control and MPT was advanced. In winter, MPV was insignificantly higher in comparison to preflight control and MPT was almost unchanged. While changes in MPV do not depend on season, flight direction and day of stay after flight than MPT was differentiated seasonally and due to direction of flight. MPV and MPT were significantly modified by characteristics of individual light exposure during daytime and evening. The experiment showed also that in real conditions activity level is an important factor affected melatonin peak in tourists. In winter, greater daytime activity significantly influenced earlier MPT occurrence, both after northward and southward flights.

Melatonin deficiencies in women.

The pineal hormone melatonin is the mediator of external light to physiologic adaptation to day and night rhythms, it regulates reproduction in animals but attempts to utilize melatonin in women for contraception have failed. Melatonin seems to be the natural hormone to facilitate sleep in insomniac patients and causes no hang over. When applied together with benzodiazepine it allows reduction of benzodiazepine without withdrawal effects. It should be applied 2 h before sleeping time in doses between 3 and 5 mg. Melatonin acts via the gamma-aminobutyric acid- and benzodiazepine receptor explaining its success in treatment of seizures in children and in adults. Constant application of benzodiazepine reduced the production of natural melatonin in rats, supporting the evidence that long-term application of benzodiazepine in humans does not restore sleeping habits but reduces natural sleeping habits even more. Low melatonin levels were seen in bulimia or neuralgia and in women with fibromyalgia; replacement reduced pain, sleeping disorders, and depression in fibromyalgia and bulimia. Melatonin profiles are a diagnostic tool to distinguish between several forms of depression, like major depression, winter depression (SAD), unipolar depression, delayed sleep phase syndrome (DSPS). In patients with a major depression success with antidepressants correlated with an increase in their melatonin profiles but only patients suffering from DSPS can be successfully treated with melatonin. In perimenopausal women melatonin administration did produce a change in LH, FSH and thyroid hormones. Some oncostatic properties are supported by cell culture work and studies in animals. In Nordic countries indigenous people suffer less from breast and prostate cancer, winter darkness seems to protect. The supposedly increased melatonin levels created the 'melatonin hypothesis'. Epidemiological studies did show that blind people indeed have half the rate of breast cancers, supporting the hypothesis. Controversial results concerning melatonin and insulin resistance and glucose tolerance have been published. In postmenopausal women application of melatonin reduced glucose tolerance and insulin sensitivity. Pregnant women should avoid melatonin, since its teratogenic effect is not known. Patients suffering from non-hormone dependent tumors, like leukemia, should avoid melanin, since tumor growth was promoted in animal experiments. It can be expected that melatonin will receive wide consideration for treatment of sleeping disturbances, jet lag, and fibromyalgia once an oral formulation becomes available in Europe.

Resynchronization of blood pressure circadian rhythm after westward trans-7-meridian flight with and without melatonin treatment.

Blood pressure (BP) of a healthy 37-yr-old male traveling from Milan to Houston was monitored for 36 h before the flight and continued for 5 d after the arrival. The rhythmometric analysis of BP data was made to investigate the rate of adaptation to a rapid rest-activity cycle shift. Since two trips were evaluated, during the second one the subject took melatonin (3 mg) before the nocturnal rest. In the first trip the BP circadian rhythm synchronization occurred on the 5th day. In the second trip melatonin promoted an immediate but unstable adaptation to the new rest-activity cycle.

The possible effects on health, comfort and safety of aircraft cabin environments.

A consultation was undertaken to investigate the views and concerns of stakeholders in the aircraft industry about the possible harmful effects on personal health, comfort and safety of aircraft cabin environments. Stakeholders were identified from a variety of sources including Government agencies, the Internet, House of Lords inquiry, and suggestions of interviewees. They represented: aircraft crews, aircraft constructors and engineers, government departments and authorities, holiday/flight companies, insurance companies, non-governmental organisations, occupational health physicians, passenger representatives, and independent researchers and consultants. Eighty-seven were contacted of which 57 were interviewed over the telephone using a semi-structured questionnaire. Their concerns were transcribed into a standard format and analysed qualitatively. Key stakeholders, along with Government officials, were invited to a workshop to discuss and prioritize the issues raised during the interviews. The main concerns expressed by the participants fell into five main areas: deep vein thrombosis, air quality, infection, cosmic radiation, and jet lag and work patterns. In addition, a number of safety concerns were raised as well as comments on the provision of appropriate advice to passengers. It was generally felt that further research was required on each of these subjects, as well as an improvement in the quality, quantity and availability of information provided for passengers prior to boarding a flight.