The circadian system affects physiological, psychological, and molecular mechanisms in the body, resulting in varying physical performance over the day. The timing and relative size of these effects are important for optimizing sport performance. In this study, Olympic swim times (from 2004 to 2016) were used to determine time-of-day and circadian effects under maximal motivational conditions. Data of athletes who made it to the finals (N = 144, 72 female) were included and normalized on individual levels based on the average swim times over race types (heat, semifinal, and final) per individual for each stroke, distance and Olympic venue. Normalized swim times were analyzed with a linear mixed model and a sine fitted model. Swim performance was better during finals as compared to semi-finals and heats. Performance was strongly affected by time-of-day, showing fastest swim times in the late afternoon around 17:12 h, indicating 0.32% improved performance relative to 08:00 h. This study reveals clear effects of time-of-day on physical performance in Olympic athletes. The time-of-day effect is large, and exceeds the time difference between gold and silver medal in 40%, silver and bronze medal in 64%, and bronze or no medal in 61% of the finals.

Sudden cardiac and cerebral events are most common in the morning. A fundamental question is whether these events are triggered by the increase in physical activity after waking, and/or a result of circadian variation in the responses of circulatory function to exercise. Although signaling pathways from the master circadian clock in the suprachiasmatic nuclei to sites of circulatory control are not yet understood, it is known that cerebral blood flow, autoregulation and cerebrovascular reactivity to changes in CO(2) are impaired in the morning and, therefore, could explain the increased risk of cerebrovascular events. Blood pressure (BP) and the rate pressure product (RPP) show marked 'morning surges' when people are studied in free-living conditions, making the rupture of a fragile atherosclerotic plaque and sudden cardiac event more likely. Since cerebral autoregulation is reduced in the morning, this surge in BP may also exacerbate the risk of hemorrhagic and ischemic strokes in the presence of other acute and chronic risk factors. Increased sympathetic activity, decreased endothelial function, and increased platelet aggregability could also be important in explaining the morning peak in cardiac and cerebral events but how these factors respond to exercise at different times of day is unclear. Evidence is emerging that the exercise-related responses of BP and RPP are increased in the morning when prior sleep is controlled. We recommend that such 'semi-constant routine' protocols are employed to examine the relative influence of the body clock and exogenous factors on the 24-h variation in other circulatory factors.

Football (soccer) training and matches are scheduled at different times throughout the day. Association football involves a variety of fitness components as well as psychomotor and game-related cognitive skills. The purpose of the present research, consisting of two separate studies, was to determine whether game-related skills varied with time of day in phase with global markers of both performance and the body clock. In the first study, eight diurnally active male association football players (19.1+/-1.9 yrs of age; mean+/-SD) with 10.8+/-2.1 yrs playing experience participated. Measurements were made on different days at 08:00, 12:00, 16:00, and 20:00 h in a counterbalanced manner. Time-of-day changes in intra-aural temperature (used as a marker of the body clock), grip strength, reaction times, flexibility (markers of aspects of performance), juggling and dribbling tasks, and wall-volley test (football-specific skills) were compared. Significant (repeated measures analysis of variance, ANOVA) diurnal variations were found for body temperature (p<0.0005), choice reaction time (p<0.05), self-rated alertness (p<0.0005), fatigue (p<0.05), forward (sit-and-reach) flexibility (p<0.02), and right-hand grip strength (p<0.02), but not left-hand grip strength (p=0.40) nor whole-body (stand-and-reach) flexibility (p=0.07). Alertness was highest and fatigue lowest at 20:00 h. Football-specific skills of juggling performance showed significant diurnal variation (p<0.05, peak at 16:00 h), whereas performance on the wall-volley test tended to peak at 20:00 h and dribbling showed no time-of-day effect (p=0.55). In a second study, eight diurnally active subjects (23.0+/-0.7 yrs of age) completed five test sessions, at the same times as in the first study but with a second session at 08:00 h. Test-re-test comparisons at 08:00 h for all components indicated good reliability. Intra-aural temperature showed a significant time-of-day effect (p<0.001) with mean temperature at 16:00 h (36.4 degrees C) higher than at 08:00 h (35.4 degrees C). There was no significant effect of chronotype on the temperature acrophase (peak time) (p>0.05). Diurnal variation was found for performance tests, including sit-and-reach flexibility (p<0.01) and spinal hyper-extension (p<0.05). Peaks occurred between 16:00 and 20:00 h and the daytime changes paralleled the temperature rhythm. Diurnal variation was also found for football-specific tests, including dribbling time (p<0.001, peak at 20:00 h) and chip test performance (p<0.01), being more accurate at 16:00 h (mean error=0.75 m) than at 08:00 h (mean error=1.01 m). Results indicate football players perform at an optimum between 16:00 and 20:00 h when not only football-specific skills but also measures of physical performance are at their peak. Body temperature peaked at a similar time, but positive mood states seemed to peak slightly earlier. While causal links cannot be established in these experiments, the results indicate that the diurnal variation of some aspects of football performance is affected by factor(s) other than body temperature alone.

There is growing awareness of the importance of circadian rhythmicity in various research fields. Exciting developments are ongoing in the field of circadian neurobiology linked to sleep, food intake, and memory. With the current knowledge of critical 'clock genes' (genes found to be involved in the generation of circadian rhythms) and novel techniques for imaging cyclic events in brain and peripheral tissue, this field of research is rapidly expanding. We reviewed only some of the highlights of the past year, and placed these findings into a mutual circadian perspective.Recent findings on the organization of the circadian clock systems are addressed, ranging from the retina to the suprachiasmatic nucleus and peripheral organs. Novel developments in sleep, food intake, and memory research linked to circadian aspects are discussed.The neurobiology of circadian rhythms is pivotal to the orchestration of the temporal organization of an individual's physiology and behavior. Endogenous circadian timing systems underlie coupling and uncoupling mechanisms of many neuronal and physiological processes, the latter possibly inducing health risks to the organism. The integration of sleep, food intake and memory in a circadian setting has clear potential as a systems neurobiology line of research.

The biological clock system is an intrinsic timekeeping device that integrates internal physiology and external cues. Maintaining a healthy biological clock system is crucial for life. Disruptions to the body’s internal clock can lead to disturbances in the sleep-wake cycle and abnormalities in hormone regulation, blood pressure, heart rate, and other vital processes. Long-term disturbances have been linked to the development of various common major diseases, including cardiovascular diseases, metabolic disorders, tumors, neuropsychiatric conditions, and so on. External factors, such as the diurnal rhythm of light, have a significant impact on the body’s internal clock. Additionally, as an important non-photic zeitgeber, exercise can regulate the body’s internal rhythms to a certain extent, making it possible to become a non-drug intervention for preventing and treating circadian rhythm disorders. This comprehensive review encompasses behavioral, physiological, and molecular perspectives to provide a deeper understanding of how exercise influences circadian rhythms and its association with related diseases.

Circadian clocks are endogenous oscillators that control 24-hour physiological and behavioural processes in organisms. These cell-autonomous clocks are composed of a transcription-translation-based autoregulatory feedback loop. With the development of next-generation sequencing approaches, biochemical and genomic insights into circadian function have recently come into focus. Genome-wide analyses of the clock transcriptional feedback loop have revealed a global circadian regulation of processes such as transcription factor occupancy, RNA polymerase II recruitment and initiation, nascent transcription, and chromatin remodelling. The genomic targets of circadian clocks are pervasive and are intimately linked to the regulation of metabolism, cell growth and physiology.

Circadian clocks are internal timekeepers enabling organisms to adapt to recurrent events in their environment – such as the succession of day and night—by controlling essential behaviors such as food intake or the sleep-wake cycle. A ubiquitous cellular clock network regulates numerous physiological processes including the endocrine system. Levels of several hormones such as melatonin, cortisol, sex hormones, thyroid stimulating hormone as well as a number of metabolic factors vary across the day, and some of them, in turn, can feedback on circadian clock rhythms. In this review, we dissect the principal ways by which hormones can regulate circadian rhythms in target tissues – as phasic drivers of physiological rhythms, as zeitgebers resetting tissue clock phase, or as tuners, affecting downstream rhythms in a more tonic fashion without affecting the core clock. These data emphasize the intricate interaction of the endocrine system and circadian rhythms and offer inroads into tissue-specific manipulation of circadian organization.

The hypothalamic suprachiasmatic nucleus (SCN) is the locus of a master clock that regulates circadian rhythms in physiology and behavior. Gonadectomy in male mice lengthens the period of circadian rhythms and increases the day-to-day variability of activity onset time. Both of these responses are rescued by the nonaromatizable androgen dihydrotestosterone. Androgen receptors (AR) are localized in SCN neurons that receive direct retinal input. To explore how androgens affect circadian clock function and its responsiveness to photic cues, we measured wheel-running behavior and SCN AR expression in intact, gonadectomized, and testosterone-replaced mice, held under various photic conditions. Gonadectomy lengthened circadian period in constant dim light but not in constant darkness. Increasing intensities of constant light parametrically increased circadian period, and this was potentiated at all intensities by gonadectomy. In contrast, gonadectomy did not alter light-induced pupil constriction, suggesting a nonretinal locus of hormone action. In hormone-replaced animals housed in constant darkness, T concentration was positively correlated with precision of activity onset and with SCN AR expression and negatively correlated with duration of activity. We infer the existence of two androgenic mechanisms: one modulates SCN responsiveness to light, and the second modulates SCN timekeeping and locomotor activity in a dose-dependent manner. Finally, the effects of androgens on period are a result of hormonal modulation of the SCN's response to photic input rather than to a change in the inherent period of oscillators in the absence of light.

目的: 研究褪黑素(melatonin，MT)干预肺纤维化患者节律基因表达，并分析其缓解肺纤维化疾病进展的机制。方法: 通过高通量基因表达数据库(Gene Expression Omnibus，GEO)筛选肺纤维化患者与健康对照组之间差异表达的生物钟基因，分析节律基因与肺功能及肺纤维化相关基因之间的相关性。构建博来霉素(bleomycin，BLM)诱导小鼠肺纤维化模型，通过测序及免疫组织化学染色观察BLM组以及使用MT干预后(BLM+MT组)肺组织PER2、CRY2表达的差异，通过HE染色及Masson染色观察MT对肺纤维化的影响。用Western blot检测转化生长因子β(transforming growth factor β，TGF-β)诱导肺上皮细胞P-smad2/3的表达，采用实时荧光定量逆转录PCR技术，探究对照组、TGF-β组、TGF-β+MT组生物钟基因的节律表达变化，最后通过MT受体阻滞剂luzindole干预TGF-β+MT组的肺上皮细胞，通过Western blot探究MT减轻TGF-β诱导上皮-间质转化的受体依赖性。结果: (1) 通过对GEO数据集的分析发现，节律基因PER2和CRY2与TGF-β的表达存在负相关性，且与患者肺功能指标存在正相关性。(2)小鼠肺组织转录组测序分析发现BLM组PER2和CRY2的表达较正常组明显减少。同时，病理染色结果显示正常组小鼠肺组织结构完整清晰，肺泡间隔薄；BLM组中肺组织出现大量胶原纤维增生，肺泡结构紊乱；与BLM组相比，BLM+MT组胶原纤维增生及炎性细胞浸润减少；免疫组化染色结果提示BLM组PER2和CRY2的表达量比正常组降低，BLM+MT组比BLM组增加。(3)肺上皮细胞体外TGF-β干预实验结果表明，相较于对照组，TGF-β组P-smad2/3表达量增加，MT干预抑制了TGF-β对P-smad2/3的诱导作用，而MT受体阻滞剂干预又逆转了这一现象，说明MT可以抑制TGF-β通路激活，且该过程存在MT受体依赖性。(4)肺上皮细胞48 h节律实验结果显示，TGF-β+MT组中PER2和CRY2的mRNA节律接近24 h，且有向对照组节律恢复的趋势，而在加入MT受体阻断剂后，其节律的时程和振幅均趋向于TGF-β组。结论: MT通过与其受体结合，可以恢复正常生物钟基因PER2和CRY2的周期性表达，进而抑制TGF-β经典通路的激活，抑制肺纤维化上皮-间质转化病理进程。这一发现为肺纤维化的治疗提供了新的分子靶点和潜在的治疗策略。

An English language self-assessment Morningness-Eveningness questionnaire is presented and evaluated against individual differences in the circadian vatiation of oral temperature. 48 subjects falling into Morning, Evening and Intermediate type categories regularly took their temperature. Circadian peak time were identified from the smoothed temperature curves of each subject. Results showed that Morning types and a significantly earlier peak time than Evening types and tended to have a higher daytime temperature and lower post peak temperature. The Intermediate type had temperatures between those of the other groups. Although no significant differences in sleep lengths were found between the three types, Morning types retired and arose significantly earlier than Evening types. Whilst these time significatly correlated with peak time, the questionnaire showed a higher peak time correlation. Although sleep habits are an important déterminant of peak time there are other contibutory factors, and these appear to be partly covered by the questionnaire. Although the questionnaire appears to be valid, further evaluation using a wider subject population is required.

The interest in the systematic study of the circadian typology (CT) is relatively recent and has developed rapidly in the two last decades. All the existing data suggest that this individual difference affects our biological and psychological functioning, not only in health, but also in disease. In the present study, we review the current literature concerning the psychometric properties and validity of CT measures as well as individual, environmental and genetic factors that influence the CT. We present a brief overview of the biological markers that are used to define differences between CT groups (sleep-wake cycle, body temperature, cortisol and melatonin), and we assess the implications for CT and adjustment to shiftwork and jet lag. We also review the differences between CT in terms of cognitive abilities, personality traits and the incidence of psychiatric disorders. When necessary, we have emphasized the methodological limitations that exist today and suggested some future avenues of work in order to overcome these. This is a new field of interest to professionals in many different areas (research, labor, academic and clinical), and this review provides a state of the art discussion to allow professionals to integrate chronobiological aspects of human behavior into their daily practice.

The purpose of this study was to describe and compare the circadian rhythm of body temperature and cortisol, as well as self-reported clock times of sleep onset and offset on weekdays and weekends in 19 healthy adult "larks" (morning chronotypes) and "owls" (evening chronotypes), defined by the Home and Ostberg questionnaire. Day-active subjects entered the General Clinical Research Center, where blood was sampled every 2 h over 38 h for later analysis for cortisol concentration by enzyme immunoassay. Rectal body temperature was measured continuously. Lights were turned off at 22:30 for sleep and turned on at 06:00, when subjects were awakened. The acrophases (peak times) of the cortisol and temperature rhythms occurred 55 minutes (P < or =.05) and 68 minutes (P <.01), respectively, earlier in the morningness group. The amplitude of the cortisol rhythm was lower in the eveningness than in the morningness group (P = n.s.). Subject groups differed on all indices of habitual and preferred timing of sleep and work weekdays and weekends (P =.05-.001).

Two types of sleep preference have been supported in the literature. Morning types awaken early and are refreshed upon waking, whereas Evening types rise later and have more erratic sleep schedules. Sleep affects menstrual functioning in adult women. However, there is scant research on the association between sleep preference and menstrual functioning in adolescents. Thus, the present study examined the association between sleep preference and menstrual functioning in 210 adolescent girls (11-17 years old).Data represent baseline measures from a longitudinal study examining the association of psychological functioning and smoking with reproductive and bone health. Measures included the Menstrual Symptom Questionnaire (MSQ), regularity and duration of menstrual cycles, and the Morningness/Eveningness scale (measuring sleep preference). MSQ factor scores were used in analyses: abdominal pain, negative affect/somatic complaints, back pain, and anxiety/fatigue.The results from hierarchical linear regression analyses showed significant associations between Evening preference and more symptoms of abdominal pain (P<.01), negative affect/somatic complaints (P<.01), anxiety/fatigue (P<.01), and shorter menses (P<.05).Adolescent girls with Evening preference experience more menstrual symptoms than those with Morning preference. Future research should include sleep preference in studies of health and behavior particularly in adolescence when there is a normative shift toward Evening preference.

Circadian rhythms, cyclic fluctuations in many physiological and psychological functions, are thought to influence adjustment to shiftwork. A widely acknowledged individual difference in circadian rhythms, commonly called morningness, indicates preferences associated with morning or evening activities. Various self-report instruments have been developed to measure morningness, although little measurement data have been published for these scales. Because morningness scales are being used to select workers for night shiftwork, psychometric evaluations of these scales are needed. Psychometric assessments of undergraduate responses (N = 501) on three widely used scales indicate internal (interitem) measurement deficiencies in all three. Therefore, a 13-item scale was developed that distills the best items from two of these scales. Relationships between the new composite scale and external criteria are comparable with or stronger than similar relationships between the published scales and external criteria.

Circadian rhythms play an influential role in nearly all aspects of physiology and behavior in the vast majority of species on Earth. The biological clockwork that regulates these rhythms is dynamic over the lifespan: rhythmic activities such as sleep/wake patterns change markedly as we age, and in many cases they become increasingly fragmented. Given that prolonged disruptions of normal rhythms are highly detrimental to health, deeper knowledge of how our biological clocks change with age may create valuable opportunities to improve health and longevity for an aging global population. In this Review, we synthesize key findings from the study of circadian rhythms in later life, identify patterns of change documented to date, and review potential physiological mechanisms that may underlie these changes.

Rest-activity rhythm (RAR), a manifestation of circadian rhythms, has been associated with morbidity and mortality risk. However, RAR patterns in the general population and specifically the role of demographic characteristics in RAR pattern have not been comprehensively assessed. Therefore, we aimed to describe RAR patterns among non-institutionalized US adults and age, sex, and race/ethnicity variation using accelerometry data from a nationally representative population.

The relation between morningness (M) - eveningness (E) and lifestyle regularity was studied in a convenience sample of 100 healthy subjects aged between 20 and 59 yrs (47 males and 53 females; mean age 33.6 yrs). Morningness-eveningness was measured by a single administration of the 13-item Composite Scale for Morningness (CSM). Lifestyle regularity was measured by requiring subjects to complete a five-item Social Rhythm Metric diary (SRM-5) each evening for two weeks. Each week of SRM-5 was analyzed separately and the two SRM scores averaged to yield the lifestyle regularity measure for the subject. Subjects were categorized by morningness into top and bottom quartiles of CSM score (denoted M-types and E-types, respectively), with the remaining 50% of subjects denoted as intermediate (I-types). Mean SRM scores significantly differed between the three morningness groups (p <0.001) in the order E-types (SRM = 3.6), then I-types (SRM=4.0), then M-types (SRM=4.9), with higher scores indicating greater daily lifestyle regularity. The effect size of the E-type versus M-type difference was approximately 1.3. The relationship between the CSM and SRM scores was also confirmed using a correlational analysis (rho = 0.428; p < 0.001). This correlational finding was substantially weaker when age was partialed out (r=0.186; p=0.065), although there was still a trend toward a significan relationship. Thus it appears that morning types appear to be more regular in their daily lifestyle than are evening types, suggesting a relationship between these two aspects of human circadian behavior.

Humans show large inter-individual differences in organising their behaviour within the 24-h day-this is most obvious in their preferred timing of sleep and wakefulness. Sleep and wake times show a near-Gaussian distribution in a given population, with extreme early types waking up when extreme late types fall asleep. This distribution is predominantly based on differences in an individuals' circadian clock. The relationship between the circadian system and different "chronotypes" is formally and genetically well established in experimental studies in organisms ranging from unicells to mammals. To investigate the epidemiology of the human circadian clock, we developed a simple questionnaire (Munich ChronoType Questionnaire, MCTQ) to assess chronotype. So far, more than 55,000 people have completed the MCTQ, which has been validated with respect to the Horne-Østberg morningness-eveningness questionnaire (MEQ), objective measures of activity and rest (sleep-logs and actimetry), and physiological parameters. As a result of this large survey, we established an algorithm which optimises chronotype assessment by incorporating the information on timing of sleep and wakefulness for both work and free days. The timing and duration of sleep are generally independent. However, when the two are analysed separately for work and free days, sleep duration strongly depends on chronotype. In addition, chronotype is both age- and sex-dependent.

The aims of this study were to examine the genetic and environmental influences on diurnal preference and sleep quality, the association between these phenotypes, the genetic and environmental influences on this association, and the magnitude of overlap between these influences. Using a twin design, data on diurnal preference (measured by the Morningness-Eveningness Questionnaire) and sleep quality (measured by the Pittsburgh Sleep Quality Index) were collected from 420 monozygotic twins, 773 dizygotic twins, and 329 siblings (mode age = 20 yrs, range = 18-27 yrs) from a population-based twin registry across the UK. Univariate analyses indicated that dominance genetic influence accounted for 52% and non-shared environment 48% of variance in diurnal preference. For sleep quality, additive genetic influence explained 43% and non-shared environment 57% of the variance. The bivariate analysis indicated a significant association between greater eveningness preference and poorer sleep quality (r =.27). There was substantial overlap in the additive genetic influences on both phenotypes (rA =.57), and overlap in the dominance genetic influences common to both phenotypes was almost absolute (rD =.99). Overlap in non-shared environment was much smaller (rE =.02). Additive genetic influence accounted for 2% of the association, dominance genetic influence accounted for 94%, and non-shared environmental influences accounted for the remaining 4%. The substantial overlap in genetic influence between these phenotypes indicates that similar genes are important for diurnal preference and sleep quality. Therefore, those genes already known to influence one phenotype may be possible candidates to explore with regards to the other phenotype.

Morningness-eveningness preference by the self-rated Morningness-Eveningness Questionnaire (MEQ) has earlier been shown to be associated with the subjects' season of birth. Here, we obtain this result for a new sample of 2,125 university students and for the sample obtained by pooling the data with the earlier study, yielding totally 3,709 Italian and Spanish subjects. An nonlinear regression of MEQ as a cosine curve according to the month of birth, adjusting for age and gender, gave a maximum (morningness) around the transition between the birth months December and January, and a minimum (eveningness) around the transition between the birth months June and July. Multiple logistic regressions showed that for females as well as for males, the group born during the half-year April to September containing summer had a significantly lower proportion of morning types as compared with the group born during the half-year October to March containing winter. This was more pronounced for males. Moreover, a significantly higher proportion of morning types among females compared with males was found only in the group born during April to September, but not in the group born during October to March. There was a weak but statistically significant positive correlation between MEQ and age in the sample's limited age range of 17-30 years. We discuss the results in terms of the mutually inhibitory systems of melatonin and dopamine, and find further support for a hypothesis that it is the variation in the length of photoperiod during the gestational or perinatal period that contributes significantly to the season of birth variation found in the morningness-eveningness preference among adults.Copyright 2003 S. Karger AG, Basel

The study investigates the effect of the month of birth and ambient light conditions at birth on sleep length and chronotype among residents of high latitudes. The authors surveyed 1172 persons (609 girls, 563 boys) age 11 to 18 yrs living in five villages and four towns located between 59.5°N and 67.6°N latitude. Survey participation was voluntary and anonymous. Sleep length and chronotype were assessed using the Munich chronotype questionnaire (MCTQ). The study showed the sleep length and chronotype of the children and adolescents depended on sex, age, type of settlement (town/village), and latitude of residence. Latitude exerted a stronger impact on sleep length and chronotype of children and adolescents living in villages than on those of their urban counterparts. Month of birth had no effect on sleep length and chronotype. There was a significant effect of the time of sunrise, sunset, and day length at birth on the chronotype of children and adolescents. A later chronotype was observed in the sample of young persons living above the Arctic Circle who were born during the polar day and polar night.

Several studies suggest that season of birth differentially affects the physiological characteristics of humans. Those living at relatively high latitude, such as Canada, Spain, and Italy (44°N-45°N), and born in the fall tended to be "morning-type" persons in comparison to those born in other seasons. There are relatively little data on the affect of season of birth on people residing at low latitude. Here the authors show that at low latitude, Kochi, Japan (33°N), the effect of season of birth on the morningness chronotype is confined to young children aged 1-12 yrs, disappearing in elderly persons. Only female participants aged 2-12 yrs born in the fall, especially in November, were significantly morning-typed (p <.001) in comparison to those born in the other seasons, whereas there were no such significant season-of-birth differences in morningness-eveningness preference among male participants. Moreover, both female and male participants aged 13-25 yrs showed no significant seasonal differences in morningness-eveningness preference. The small effects detected in this study might be due to smaller seasonal change in day length at the relatively lower latitude of Kochi.

The present study explored the possible role of the photoperiod at birth on morningness by collecting data in the northern (Italy) and southern (Australia) hemispheres. To assess circadian typology, the Composite Scale of Morningness (CS) was administered to a sample of 1734 university students (977 Italian and 757 Australian; 1099 females and 635 males; age 24.79 ± 7.45 yrs [mean ± SD]). Consistent with the literature, females reported higher CS scores (morningness) than males, and Australian participants reported higher CS scores than Italian participants. Allowing for the fact the seasons are reversed between the hemispheres, the results are in line with previous studies. The authors found more evening types were born during the seasons associated with longer photoperiod (spring and summer), and more morning types were born during the seasons associated with shorter photoperiod (autumn and winter), indirectly supporting an imprinting-like phenomenon played by the photoperiod at birth.

With informed consent, 6 competitive tennis players performed alternate 15 “first” (emphasis-speed) serves and 15 “second” (emphasis-accuracy) serves at 09:00, 14:00 and 18:00 hours. Serve velocity was measured by the digitisation of video footage of each serve. The Hewitt Tennis Achievement Test was employed to measure the accuracy of serve. The amount of spin imparted on the ball was not measured. First serves were at all times of day faster than second serves. First serves were faster but least accurate at 18:00 hours, the time of day that body temperature and grip strength were highest. At 09:00 hours, first serves were just as accurate as second serves, even though velocity of first serves was higher. No effects for time of day were found for the speed and accuracy of second serves. These results indicate that time of day does affect the performance of tennis serves in a way that suggests a nonlinear relationship between velocity and accuracy.

Tennis players’ success relies on tennis skills, such as groundstrokes and serves, and physical attributes, such as strength, speed and endurance. This study aimed to determine if players’ tennis skills and physical attributes are influenced by time of day, chronotype or sleep–wake behaviour (SWB). Twelve male tennis players (age (years): 28.17 ± 7.85) competing in state-level competitions wore a wrist-worn activity monitor (GT3X, Actigraph) and completed a modified version of the Consensus Sleep Diary to measure SWB. The Chalder Fatigue Scale and Morningness and Eveningness Questionnaire were used to measure players’ fatigue and preferred chronotype. Mid-sleep with a sleep correction was used to determine players’ current chronotype. After the baseline period, players were tested at 8:00 am, 2:00 pm and 8:00 pm, with the order of testing sessions randomised for each player. Testing sessions were separated by at least 48 hours. Players’ groundstrokes, serve speed, agility, overhead medicine ball throw and Hit and Turn Test performance were measured in each session. General linear modelling revealed that backhand consistency was less in the evening compared to the morning by 17% (p = 0.020) and afternoon by 15% (p = 0.040). Maximal service velocity was less in the evening compared to the afternoon by 10.5 km/h (p = 0.041). Chronotype did not influence tennis skills or physical performance. Average and maximal backhand velocities were reduced for every hour that time at lights out, and sleep-onset time was postponed. Tennis skills, but not physical performance tests, were influenced by time of day and SWB.

Circadian rhythms are internal mechanisms that regulate various aspects of the human body's physiology and behaviour that are influenced by activity, physicality, and change time in 24 hours. This study aims to compare oxidant levels and hormonal levels based on differences in training times, namely morning and evening, in badminton athletes. This research involved 44 badminton athletes using a purposive sampling technique who were divided into a morning group (n = 22) and an evening group (n = 22). Melatonin levels were measured using the Elabscience Kit (No. E-EL-H2016) and malondialdehyde (MDA) levels using spectrophotometry. All research procedures have received ethical approval from the Hasanuddin University Medical Faculty Ethics Commission (Number: 377/UN4.6.4.5.31/PP36/2023). The results of this study indicate that the athlete's melatonin value in the morning was 76.71 ± (29.05-247.45) higher than in the evening 80.43 ± (50.83-155.24) Meanwhile, the athlete's MDA value in the evening was 2.08 ± (0.74–4.57) higher compared to the MDA in the morning of 1.09 ± (0.33–3.71). Meanwhile, based on the insomnia value for evening training, a higher value was obtained compared to morning training, namely 9.50 ± (3-11). However, there was no significant difference in stress levels. The results of the study showed that badminton athletes who trained at night tended to experience sleep disturbances (insomnia) and increased oxidant levels, while hormonal levels, especially melatonin, were higher in athletes who trained in the morning.

People can be classified into three chronotypes (CT): morning-type (M-type), Neither-type (N-type) and Evening-type (E-type). M-types perform better in the morning, E-types in the evening. It seems that bad sleep worsens physical performance. The impact of sleep and CT on specific sports and populations is unclear. Therefore, we wanted to assess agility, strength and endurance in young soccer players in relation to their sleep and chronotype. 58 players (13–19 years) were recruited. Sleep and CT were assessed by questionnaires. The physical trial was performed at 8:30 a.m. and 6:00 p.m., and included three tests to determine agility, strength and endurance. The sample was classified by CT as M-types (n = 11), N-types (n = 29) and E-types (n = 18). Furthermore, they were categorized as people with Good Sleep/Wake quality (GSW, n = 28) and people with Bad Sleep/Wake quality (BSW, n = 30). Comparing the three CTs in the aerobic test, M-types performed better in the morning (p = 0.01), while E-types in the evening (p &lt; 0.001). GSW performed better than BSW (p = 0.019) in the aerobic test in the p.m. session. These results underline the difference in aerobic power between M-and E-types during the morning and evening session; moreover, they show a difference in p.m. aerobic performance according to sleep quality.

Circadian rhythms influence daily behavior, psychological and physiological functions, as well as physical performance. Three chronotypes are distinguished according to the preferences people typically display for activity at certain times of day: Morning, Neither, and Evening types (M-, N- and E-types). The chronotype changes with age: eveningness tends to be stronger in youth and morningness in older age. The progressive shift toward eveningness during adolescence creates misalignment with morning society schedules and can lead to a deterioration in intellectual and physical performance. Soccer is one of the world's most popular sports practiced by adolescents and soccer workouts are usually held after school in the afternoon or evening. Performance in soccer is related to a host of factors, including physiological variables and motor skills that have a circadian variation. The aim of this study was to determine the effect of chronotype on motor skills specific to soccer, specifically whether agility, aerobic endurance, and explosive power differ among the three chronotypes in relation to the time of day. For this study 141 adolescent soccer players filled in the Morningness-Eveningness Questionnaire (MEQ) for the assessment of chronotype. A subsample of 75 subjects, subdivided in M-types (n= 25), E-types (n= 25), and N-types (n= 25), performed three tests (Sargent Jump Test - SJT, Illinois Agility Test - IAT, and 6-Minutes Run Test - 6MRT) at a morning and an evening training session (9:00 am and 6:00 pm). Mixed ANOVA was used to test the interactions between chronotypes, physical performance, and time. On all tests, better performance during the morning than the evening session was observed for the M-types (< .05), whereas the E-types performed better in the evening than in the morning session (< .05), and no differences in test performance were detected for the N-types. These findings underline the importance of a correct chronobiological approach to sports training. Scheduling training sessions according to an athlete's circadian preferences could be a valid strategy to enhance performance.

The purposes of this study were to determine: 1) morning-to-evening differences in physical performance with and without a ball; and 2) associations between sleep outcomes (duration and quality) and physical performance in handball players. Sixteen elite, male handball players (25.4 ± 5.8 yr, 94.0 ± 7.4 kg, 193.5 ± 7.5 cm) completed physical performance tests without a ball (a zig-zag test assessing closed-skill agility, linear sprints, and countermovement (CMJ) and squat jumps) and with a ball (a zig-zag test and linear sprints) in the morning and evening. In addition, sleep quality and quantity during the night before testing were obtained using self-reported measures. Superior physical performance was evident in all tests during the evening compared to the morning hours (p < 0.003). Specifically, jump height was moderately (effect size (ES) = 0.73 to 1.02) higher during the evening. Similarly, moderate (ES = 1.17) and large (ES = 1.67) improvements in zig-zag test performance were apparent during the evening with and without the ball, respectively. Also, large to very large (ES = 1.29 to 2.09) increases in sprint performance with and without the ball were evident in the evening. No significant correlations (p > 0.05) were apparent between sleep duration and quality and physical performance in both the morning and evening sessions. Diurnal variations in physical performance were apparent in elite male handball players with enhanced performance with and without the ball in the evening compared to morning hours. These findings indicate that morning-to-evening differences in physical performance should be considered when developing conditioning plans or preparing for competition in handball.

The present study was designed to investigate if the suggested greater fatigability during repeated exercise in the afternoon, compared to the morning, represents a true time-of-day effect on fatigability or a consequence of a higher initial power. In a counterbalanced order, eight subjects performed a repeated-sprint test [10 x (6 s of maximal cycling sprint + 30 s of rest)] on three different occasions between: 08:00-10:00, 17:00-19:00, and 17:00-19:00 h controlled (17:00-19:00 h(cont), i.e., initial power controlled to be the same as the two first sprints of the 08:00-10:00 h trial). Power output was significantly (p < 0.05) higher for sprints 1, 2, and 3 in the afternoon than in the morning (e.g., sprint 1: 23.3 +/-1 versus 21.2 +/-1 W.kg(-1)), but power decrement for the 10 sprints was also higher in the afternoon. Based on the following observations, we conclude that this higher power decrement is a consequence of the higher initial power output in the afternoon. First, there was no difference in power during the final five sprints (e.g., 20.4 +/-1 versus 19.7 +/-1 W.kg(-1) for sprint 10 in the afternoon and morning, respectively). Second, the greater decrement in the afternoon was no longer present when participants were producing the same initial power output in the afternoon as in the morning. Third, electromyographic activity of the vastus lateralis decreased during the exercise (p < 0.05), but without a time-of-day effect.

Although individual athletic performance generally tends to peak in the evening, individuals who exhibit a strong diurnal preference perform better closer to their circadian peak. Time-of-day performance effects are influenced by circadian phenotype (diurnal preference and chronotype-sleep-wake patterns), homeostatic energy reserves and, potentially, genotype, yet little is known about how these factors influence physiological effort. Here, we investigate the effects of time of day, diurnal preference, chronotype, and (a circadian clock gene) genotype on both effort and performance in a population of Division I collegiate swimmers (n = 27). Participants competed in 200m time trials at 7:00 and 19:00 and were sampled pre- and post-trial for salivary α-amylase levels (as a measure of physiological effort), allowing for per-individual measures of performance and physiological effort. Hair samples were collected for genotype analysis (a variable-number tandem-repeat (VNTR) and a single nucleotide polymorphism (SNP) in ). Our results indicate significant and parallel time-of-day by circadian phenotype effects on swim performance and effort; evening-type swimmers swam on average 6% slower with 50% greater α-amylase levels in the morning than they did in the evening, and morning types required 5-7 times more effort in the evening trial to achieve the same performance result as the morning trial. In addition, our results suggest that these performance effects may be influenced by gene (circadian clock gene variants) by environment (time of day) interactions. Participants homozygous for the length variant (rs57875989) or who possess a single G-allele at SNP rs228697 swam 3-6% slower in the morning. Overall, these results suggest that intra-individual variation in athletic performance and effort with time of day is associated with circadian phenotype and genotype.

The effect of time of day on all-out swim performances was examined. Fourteen subjects performed maximal front crawl swim tests on separate days over 100 m. and 400 m. at 5 different times of day between 06.30 h. and 22.00 h. Performance showed a significant linear trend with time of day in close though not exact association with the circadian rhythm in oral temperature: a goodness of fit test confirmed that the values predicted from linear trend analysis coincided with the measured values (p less than 0.05). The steady improvement throughout the day was 3.5% for 100 m. and 2.5% for 400 m. swims. Trunk flexibility displayed a time of day variation with a trough in the morning and a peak in the afternoon. No significant rhythm was observed in ankle and shoulder flexibility, grip strength or peak expiratory flow rate (p greater than 0.05). It was concluded that maximal swimming trials are best scheduled for the evening and worst in the early morning. Specific fitness factors cannot clearly account for the higher exercise capability in the evening which is strongly related to the circadian curve in body temperature.

The aim of this study was to compare morning and evening time-trial performance, RPE and mood state of trained swimmers, taking into account chronotype, habitual training time-of-day and PERIOD3 (PER3) variable number tandem repeat genotype.Twenty-six swimmers (18 males, age: 32.6 ± 5.7 years) swam 200 m time trials (TT) at 06h30 and 18h30 in a randomised order.There was no difference between morning and evening performance when the swimmers were considered as a single group (06h30: 158.8 ± 22.7 s, 18h30: 158.5 ± 22.0 s, p = 0.611). However, grouping swimmers by chronotype and habitual training time-of-day allowed us to detect significant diurnal variation in performance, such that morning-type swimmers and those who habitually train in the morning were faster in the 06h30 TT (p = 0.036 and p = 0.011, respectively). This was accompanied by lower ratings of perceived exertion (RPE) scores post-warm-up, higher vigour and lower fatigues scores prior to the 06h30 TT in morning-type swimmers or those who trained in the morning. Similarly, neither types and those who trained in the evenings had lower fatigue and higher vigour prior to the 18h30 TT.It appears that both chronotype and habitual training time-of-day need to be considered when assessing diurnal variation in performance. From a practical point of view, athletes and coaches should be aware of the potentially powerful effect of training time on shifting time-of-day variation in performance.

Previous findings of time-of-day differences in athletic performance could be confounded by diurnal fluctuations in environmental and behavioral "masking" factors (e.g., sleep, ambient temperature, and energy intake). The purpose of this study was to examine whether there is a circadian rhythm in swim performance that is independent of these masking factors. Experienced swimmers (n = 25) were assessed for 50-55 consecutive hours in the laboratory. The swimmers followed a 3-h "ultra-short" sleep-wake cycle, involving 1 h of sleep in darkness and 2 h of wakefulness in dim light, that was repeated throughout the observation. The protocol distributes behavioral and environmental masking factors equally across the 24-h period. Each swimmer was scheduled to perform six maximal-effort 200-m swim trials that were distributed equally across eight times of day (n = 147 trials). Each trial was separated by 9 h. A cosine fit of intra-aural temperature data established the time of the lowest body temperature (Tmin). Swim performances were z-transformed and compared across the eight times of day and across twelve 2-h intervals relative to Tmin. Analysis of covariance, controlling for trial number, revealed a significant (P < 0.001) pattern in swim performance relative to environmental and circadian times of day. Performance peaked 5-7 h before Tmin (approximately 2300) and was worst from 1 h before to 1 h after Tmin (approximately 0500). Mean swim performance was 169.5 s; circadian variation from peak to worst performance was 5.8 s. These data suggest a circadian rhythm in athletic performance independent of environmental and behavioral masking effects.

Fast swim times in morning rounds are essential to ensure qualification in evening finals. A significant time-of-day effect in swimming performance has consistently been observed, although physical activity early in the day has been postulated to reduce this effect. The aim of this study was to compare intradaily variation in race-pace performance of swimmers routinely undertaking morning and evening training (MEG) with those routinely undertaking evening training only (EOG).

The aims of the present study were to: (1) investigate the effect of a weightlifting training session and time-of-day (TOD) upon biological parameters (i.e., oral temperature, hematological, C-reactive protein (CRP), and oxidative stress) and (2) assess their possible link with muscle damage responses. Nine weightlifters (21 ± 0.5 years) performed, in a randomized order, three Olympic-Weightlifting sessions (i.e., at 08:00, 14:00, and 18:00). Blood samples were collected at rest, 3 min and 48 h after each training session. Between pre- and post-training session, ANOVA showed significant increases in oxidative stress markers at the three TODs (p < 0.01) and significant increases for creatine kinase (CK) and lactate dehydrogenase (LDH) only at 08:00 and 18:00 (p < 0.05). At rest, the results showed a significant diurnal variation for the majority of the selected parameters except for malondialdehyde (MDA), total bilirubin, and CRP with higher values observed at 18:00 (p < 0.05). After the training session, given the higher rate of increase during the morning session, these diurnal variations persisted for temperature and WBC (p < 0.01) and were suppressed for CK, LDH, uric acid (UA), catalase, and glutathione peroxidase. The main significant correlations (p < 0.001) were observed between: (1) CK and MDA (r = 0.6) and CK and UA (r = 0.66 and r = 0.82) during the morning and evening training sessions; (2) CK and CRP only during the morning session (r = 0.5); and (3) CRP and WBC during the three training sessions (r = 0.8). In conclusion, the present findings: (1) confirm that the muscle damage responses could be induced by a high level of oxidative stress and (2) suggest to avoid scheduling training sessions in the morning given the higher muscle damage, inflammatory, and oxidative responses at this TOD.

Studies of time-related biological phenomena have contributed to establishing a new scientific discipline, the chronobiology, which considers biological phenomena in relation to time. Sports activity profoundly affects the temporal organization of the organism and endocrine rhythms play a key role in the chronoorganization of individuals and are particularly important for correct physical activity. Correctly reading rhythmic hormonal variations of the human organism opens new horizons to sports medicine.This review is aimed at clarifying the relationship between endocrine rhythms and sports activities on the basis of the latest data in the literature.Data acquisition was obtained from three databases (PubMed, Scopus and SPORTDiscus), paying particular attention to reviews, meta-analysis, original and observational studies on this issue.After the description of the general characteristics and parameters of biological rhythms, the main endocrine rhythms will be described, highlighting in particular the interrelationships with sports activity and focusing on the factors which can affect negatively their characteristics and consequently the psychophysical performances of the athletes.Knowledge of this issue may allow establishing the best form of competitive or amateur activity, through the collaboration of an informed athlete and a sports physician attentive to biological rhythms. By taking into account that alteration of physiological rhythmic temporal organization can favour the onset of important diseases, including cancer, this will lead to the expected performances without impairing the correct chronoorganization of the athlete.

Chronobiology is the science concerned with investigations of time-dependent changes in physiological variables. Circadian rhythms refer to variations that recur every 24 hours. Many physiological circadian rhythms at rest are endogenously controlled, and persist when an individual is isolated from environmental fluctuations. Unlike physiological variables, human performance cannot be monitored continuously in order to describe circadian rhythmicity. Experimental studies of the effect of circadian rhythms on performance need to be carefully designed in order to control for serial fatigue effects and to minimise disturbances in sleep. The detection of rhythmicity in performance variables is also highly influenced by the degree of test-retest repeatability of the measuring equipment. The majority of components of sports performance, e.g. flexibility, muscle strength, short term high power output, vary with time of day in a sinusoidal manner and peak in the early evening close to the daily maximum in body temperature. Psychological tests of short term memory, heart rate-based tests of physical fitness, and prolonged submaximal exercise performance carried out in hot conditions show peak times in the morning. Heart rate-based tests of work capacity appear to peak in the morning because the heart rate responses to exercise are minimal at this time of day. Post-lunch declines are evident with performance variables such as muscle strength, especially if measured frequently enough and sequentially within a 24-hour period to cause fatigue in individuals. More research work is needed to ascertain whether performance in tasks demanding fine motor control varies with time of day. Metabolic and respiratory rhythms are flattened when exercise becomes strenuous whilst the body temperature rhythm persists during maximal exercise. Higher work-rates are selected spontaneously in the early evening. At present, it is not known whether time of day influences the responses of a set training regimen (one in which the training stimulus does not vary with time of day) for endurance, strength, or the learning of motor skills. The normal circadian rhythms can be desynchronised following a flight across several time zones or a transfer to nocturnal work shifts. Although athletes show all the symptoms of 'jet lag' (increased fatigue, disturbed sleep and circadian rhythms), more research work is needed to identify the effects of transmeridian travel on the actual performances of elite sports competitors. Such investigations would need to be chronobiological, i.e. monitor performance at several times on several post-flight days, and take into account direction of travel, time of day of competition and the various performance components involved in a particular sport. Shiftwork interferes with participation in competitive sport, although there may be greater opportunities for shiftworkers to train in the hours of daylight for individual sports such as cycling and swimming. Studies should be conducted to ascertain whether shiftwork-mediated rhythm disturbances affect sports performance. Individual differences in performance rhythms are small but significant. Circadian rhythms are larger in amplitude in physically fit individuals than sedentary individuals. Athletes over 50 years of age tend to be higher in 'morningness', habitually scheduling relatively more training in the morning and selecting relatively higher work-rates during exercise compared with young athletes. These differences should be recognised by practitioners concerned with organising the habitual regimens of athletes.

The number of travellers undertaking long-distance flights has continued to increase. Such flights are associated with travel fatigue and jet lag, the symptoms of which are considered here, along with their similarities, differences, and causes. Difficulties with jet lag because of sleep loss and decreased performance are emphasised. Since jet lag is caused mainly by inappropriate timing of the body clock in the new time zone, the pertinent properties of the body clock are outlined, with a description of how the body clock can be adjusted. The methods, both pharmacological and behavioural, that have been used to alleviate the negative results of time-zone transitions, are reviewed. The results form the rationale for advice to travellers flying in different directions and crossing several time zones. Finally, there is an account of the main problems that remain unresolved.

The circadian rhythm of pineal melatonin is the best marker of internal time under low ambient light levels. The endogenous melatonin rhythm exhibits a close association with the endogenous circadian component of the sleep propensity rhythm. This has led to the idea that melatonin is an internal sleep "facilitator" in humans, and therefore useful in the treatment of insomnia and the readjustment of circadian rhythms. There is evidence that administration of melatonin is able: (i) to induce sleep when the homeostatic drive to sleep is insufficient; (ii) to inhibit the drive for wakefulness emanating from the circadian pacemaker; and (iii) induce phase shifts in the circadian clock such that the circadian phase of increased sleep propensity occurs at a new, desired time. Therefore, exogenous melatonin can act as soporific agent, a chronohypnotic, and/or a chronobiotic. We describe the role of melatonin in the regulation of sleep, and the use of exogenous melatonin to treat sleep or circadian rhythm disorders.

Human behavior shows large interindividual variation in temporal organization. Extreme “larks” wake up when extreme “owls” fall asleep. These chronotypes are attributed to differences in the circadian clock, and in animals, the genetic basis of similar phenotypic differences is well established. To better understand the genetic basis of temporal organization in humans, the authors developed a questionnaire to document individual sleep times, self-reported light exposure, and self-assessed chronotype, considering work and free days separately. This report summarizes the results of 500 questionnaires completed in a pilot study. Individual sleep times show large differences between work and free days, except for extreme early types. During the workweek, late chronotypes accumulate considerable sleep debt, for which they compensate on free days by lengthening their sleep by several hours. For all chronotypes, the amount of time spent outdoors in broad daylight significantly affects the timing of sleep: Increased self-reported light exposure advances sleep. The timing of self-selected sleep is multifactorial, including genetic disposition, sleep debt accumulated on workdays, and light exposure. Thus, accurate assessment of genetic chronotypes has to incorporate all of these parameters. The dependence of human chronotype on light, that is, on the amplitude of the light:dark signal, follows the known characteristics of circadian systems in all other experimental organisms. Our results predict that the timing of sleep has changed during industrialization and that a majority of humans are sleep deprived during the workweek. The implications are far ranging concerning learning, memory, vigilance, performance, and quality of life.

Our aim was to evaluate whether age-related changes in the phase of the output of the circadian timing system (CTS) can explain age differences in habitual bedtime/wake time and in sleep consolidation parameters. Analyses focused on a group of healthy elderly people (older than 70 years) with no sleep problems and with similar subjective sleep quality as a young control group. The 2-week sleep diary data and 24h laboratory temperature recordings were examined for 70 subjects (22 young men [YM], 19 old men [OM], 29 old women [OW]). Polysomnographic (PSG) sleep data recorded during temperature data acquisition were also available for 62 subjects. These analyses made use of our recently developed technique to demask temperature rhythm data. As expected, compared to the young subjects, older subjects showed earlier habitual bedtime and wake time, more disturbed sleep, and a tendency for an earlier minimum of the circadian temperature rhythm. Despite sleep consolidation differences, the groups showed very similar habitual phase-angle differences (interval between the time occurrence of the fitted temperature minimum and habitual wake time). Both elderly and young subjects woke up on average 3 h after the temperature minimum. After controlling for the effects of age group, habitual bedtime and wake time were related to clock time phase of the circadian temperature rhythm, with an earlier phase associated with earlier habitual bedtime and wake time. None of the sleep consolidation parameters were linked to the temperature phase angle. In conclusion, sleep consolidation changes associated with healthy aging do not appear to be related to changes in the phase-angle difference between the output signal from the CTS and sleep.

To determine if a morning training session could alter afternoon physical performance. Moreover, as testosterone (T) and cortisol (C) concentrations are significant predictors of physical performance, and both show circadian declines across the day, we examined the effects of morning training on diurnal T and C responses.Eighteen semi-professional rugby union players completed this randomised and counter-balanced study.Following morning saliva collection (0900 h), players completed a control (rested), Sprint (5 × 40 m) or Weights (3 repetition-maximum [RM] bench press and squat) trial. In the afternoon (15:00 h) of each trial, a further saliva sample was collected before players completed a performance test (3 RM back squat and bench press, 40 m sprint, countermovement jump [CMJ]).Salivary T concentrations declined from am to pm under Control and Sprint, but not under Weights. Delta T, from am to pm, was greater under Control (-10.9 ± 2.4 pg ml(-1)) compared to Sprints (-6.2 ± 7.1 pg ml(-1)) and Weights (-1.2 ± 5.5 pg ml(-1)) (p ≤ 0.001). Delta C, from am to pm, was greater under Control compared to both Sprint and Weights (p<0.05). Players elicited better CMJ peak power, 40-m time, 3 RM bench and squat performance under Weights compared with Control and Sprint (p<0.05). Faster 40-m times were seen under Sprint, when compared to Control (p<0.05).Performing morning strength training is associated with improved physical performance in the afternoon. Additionally, the circadian decline in T concentrations appeared offset by morning training. However, it is unclear if T concentrations are, in part, causal of these improved responses or simply a reflective marker.Copyright © 2013 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

The purpose of this study was to determine if performing a morning total-body resistance exercise workout affects explosive power in an afternoon session. The secondary goal was to assess the usefulness of the backward overhead shot throw (BOST) as a measure of explosive power in experienced thrower in the sport of athletics. Throwers (N = 14) performed 1 control and 1 experimental trial on separate days. The control consisted of BOST and a vertical jump (VJ) testing performed in the afternoon. For the experimental trial, the participants reported for a short resistance training session in the morning then repeating the BOST and VJ testing 4-6 hours later. The BOST distance (meters) and VJ peak power (watts) were correlated in both trials (r ∼ 0.64, p < 0.05). The BOST distance improved in experimental trial over control (p < 0.05), but VJ power failed to improve. The results indicate that a morning resistance exercise bout can improve competitive throwing performance later on the same day. The results also suggest that BOST may be a useful performance testing tool for throwers in the sports of athletics.

Cells in the brain's Suprachiasmatic Nucleus (SCN) are known to regulate circadian rhythms in mammals. We model synchronization of SCN cells using the forced Kuramoto model, which consists of a large population of coupled phase oscillators (modeling individual SCN cells) with heterogeneous intrinsic frequencies and external periodic forcing. Here, the periodic forcing models diurnally varying external inputs such as sunrise, sunset, and alarm clocks. We reduce the dimensionality of the system using the ansatz of Ott and Antonsen and then study the effect of a sudden change of clock phase to simulate cross-time-zone travel. We estimate model parameters from previous biological experiments. By examining the phase space dynamics of the model, we study the mechanism leading to the difference typically experienced in the severity of jet-lag resulting from eastward and westward travel.

Jet lag is one of those common medical problems, to which most people don't give a serious thought. However, it is intricately intertwined with our normal circadian rhythm. It is classified as a sleep disorder. There is also a dearth of good scientific literature, not to mention clinical trials on the subject. Slowly but steadily, the scientific community is realizing the various deleterious health effects of jet lag and is devising innovative methods to counter them. This narrative review touches upon the etiopathogenesis, clinical manifestations and therapeutic strategies effective against the nagging problem of jet lag.

Most professional and recreational athletes perform pre-conditioning exercises, often collectively termed a 'warm-up' to prepare for a competitive task. The main objective of warming-up is to induce both temperature and non-temperature related responses to optimize performance. These responses include increasing muscle temperature, initiating metabolic and circulatory adjustments, and preparing psychologically for the upcoming task. However, warming-up in hot and/or humid ambient conditions increases thermal and circulatory strain. As a result, this may precipitate neuromuscular and cardiovascular impairments limiting endurance capacity. Preparations for competing in the heat should include an acclimatization regimen. Athletes should also consider cooling interventions to curtail heat gain during the warm-up and minimize dehydration. Indeed, although it forms an important part of the pre-competition preparation in all environmental conditions, the rise in whole-body temperature should be limited in hot environments. This review provides recommendations on how to build an effective warm-up following a 3 stage RAMP model (Raise, Activate and Mobilize, Potentiate), including general and context specific exercises, along with dynamic flexibility work. In addition, this review provides suggestion to manipulate the warm-up to suit the demands of competition in hot environments, along with other strategies to avoid heating-up.

Athletes are increasingly required to travel domestically and internationally, often resulting in travel fatigue and jet lag. Despite considerable agreement that travel fatigue and jet lag can be a real and impactful issue for athletes regarding performance and risk of illness and injury, evidence on optimal assessment and management is lacking. Therefore 26 researchers and/or clinicians with knowledge in travel fatigue, jet lag and sleep in the sports setting, formed an expert panel to formalise a review and consensus document. This manuscript includes definitions of terminology commonly used in the field of circadian physiology, outlines basic information on the human circadian system and how it is affected by time-givers, discusses the causes and consequences of travel fatigue and jet lag, and provides consensus on recommendations for managing travel fatigue and jet lag in athletes. The lack of evidence restricts the strength of recommendations that are possible but the consensus group identified the fundamental principles and interventions to consider for both the assessment and management of travel fatigue and jet lag. These are summarised in travel toolboxes including strategies for pre-flight, during flight and post-flight. The consensus group also outlined specific steps to advance theory and practice in these areas.© 2021. The Author(s), under exclusive licence to Springer Nature Switzerland AG.