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Circadian Variation in Sports Performance
Abstract
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 dmes 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 ‘momingness’, 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.
... Intense physical exercise raises cortisol, which is associated with decreased sports performance due to its catabolic effect and inhibiting protein synthesis [101,102]. The body temperature increases in the early evening [103]. It positively impacts muscle tissue by modifying components of muscular contractions, like calcium uptake and the activity of myosin ATPase [101]. ...
... Thus, what is interesting, considering the influence and daily fluctuations in cortisol and body temperature, is that it can assumed that physical activity undertaken in the second part of the day may be more efficient [102]. Additionally, it has been proven that the work rate of exercises shorter than 50 min is higher in the evening [103]. ...
... This may result from slower post-exercise reactivation of the vagus nerve for individuals with the EC in the early morning [112]. When analyzing the subjective rating of perceived exertion (RPE), there has not been any diurnal variation in the RPE, even despite a higher evening work rate [103]. Nevertheless, dissimilarities in the RPE were noted in a study conducted by Rae et al. on a group of 26 swimmers based on the timing of the individuals' training sessions. ...
The chronotype, the personal predisposition towards morning or evening activities, significantly influences health conditions, sleep, and eating regulations. Individuals with evening chronotypes are often at a higher risk for weight gain due to misalignment between their natural tendencies of functioning and social schedules, resulting in insufficient sleep, disruptions in eating habits, and decreased physical activity levels. Often, impaired glucose tolerance and changes in melatonin, adiponectin, and leptin secretion, along with alterations in the clock gene functions in subjects with evening preferences, may be predisposed to obesity. These disturbances contribute to metabolic dysregulation, which may lead to the subsequent onset of obesity complications, such as hypertension, type 2 diabetes, sleep apnea, and liver diseases. Targeting critical components of the circadian system and synchronizing people’s chronotypes with lifestyle conditions could deliver potential strategies for preventing and treating metabolic disorders. Thus, it is recommended to take a personalized chronobiological approach to maintain a normal body weight and metabolic health. Nevertheless, future studies are needed to identify the clear mechanisms between the chronotype and human health. This article provides a narrative review and discussion of recent data to summarize studies on the circadian rhythm in the context of obesity. The manuscript represents a comprehensive overview conducted between August and November 2024 using the National Library of Medicine browser (Medline, Pub-Med, Web of Science).
... Circadian rhythm (CR) refers to organisms' ability to synchronize internal timekeeping with external cues, termed "zeitgebers", as coined by chronobiologist Jürgen Aschoff [1]. Human physiological synchronization during the day is primarily triggered by 24 h light fluctuations [2,3]. ...
... This synchronization contributes to daily fluctuations in both physical and cognitive performance [2][3][4][5]. Recently, there has been a growing interest in understanding the impact of CR, mainly on physical performance, in both athletic and daily life contexts [1,6,7]. In competitive situations, whether in a strenuous working environment or elite sports conditions, individuals are required to perform effectively, both physically and mentally, as many athletic activities demand a combination of motor skills, perceptual and cognitive functions [8]. ...
... These findings suggest that PT and PTFI, which are crucial elements of strength capability, are influenced by the time of day, with improved performance in the evening. This finding could be attributed to physiological variations such as body temperature and hormonal levels that peak later in the day [1]. Such circadian changes in body temperature could potentially affect nerve conduction velocity, explaining previously observed improvements for power output, coordination and reaction time performance shown in the late afternoon [62,63]. ...
Background/Objectives: Circadian rhythm (CR) influences various physiological functions, including physical and cognitive performance, which fluctuate throughout the day. The present study aimed to investigate the combined and separate effects of CR and physical fatigue on cognitive and physical performance. Methods: A sample of 18 amateur athletes was subjected to a series of tests at three different times of the day: morning, afternoon, and evening. Fatigue was induced following an isokinetic concentric exercise combined with a 20 min treadmill run, followed by assessments of selected physical and cognitive tasks. Results: A repeated measure ANOVA did not reveal an interaction between CR and fatigue in cognitive performance (p > 0.05). However, a significant main effect of fatigue was observed in visual reaction time (VisRT) across all three timepoints. Moreover, peak torque (PT) and the peak torque fatigue index (PTFI) showed significant differences between the three times of the day, peaking in the evening. Conclusions: Although we found no interaction between CR and the physical fatigue state on selected cognitive parameters at the three times of the day, a separate effect of fatigue on cognitive performance was identified. Additionally, physical parameters exhibited peak values occurring in the evening hours. Future research should further explore underlying mechanisms that potentially influence cognitive performance at different times of the day.
... The circadian rhythm (CR) refers to organisms' ability to synchronize internal timekeeping with external cues, termed "zeitgebers," as coined by chronobiologist Jürgen Aschoff [1]. Human physiological synchronization during the day is primarily triggered by 24-hour light fluctuations. ...
... This synchronization contributes to daily fluctuations in both physical and cognitive performance [2][3][4][5]. Recently, there has been a growing interest in understanding the impact of CR mainly on physical performance in both athletic and daily life contexts [1,6,7]. In competitive situations, whether in a strenuous working environment or elite sports conditions, individuals are required to perform effectively both physically and mentally, as many athletic activities demand a combination of motor skills, as well as perceptual and cognitive functions [8]. ...
... These findings suggest that PT and PTFI, which are crucial elements of strength capability, are influenced by the time of day, with improved performance in the evening. This could be attributed to physiological variations such as body temperature and hormonal levels that peak later in the day [1]. Such circadian changes in body temperature could potentially affect nerve conduction velocity, explaining previously observed improvements for power output, coordination and reaction time performance shown in late afternoon [63,64]. ...
Circadian rhythm (CR) influences various physiological functions, including physical and cognitive performance, which fluctuate throughout the day. The present study aimed to investigate the combined and separate effects of CR and physical fatigue on cognitive and physical performance. A sample of 18 amateur athletes was subjected to a series of tests at three different times of the day: morning, afternoon, and evening. Fatigue was induced following isokinetic concentric exercise combined with a 20-minute treadmill run, followed by assessments of selected physical and 18
cognitive tasks. Repeated measures ANOVA did not reveal an interaction between CR and fatigue in cognitive performance (p > 0.05). However, a significant main effect of fatigue was observed in visual reaction time (VisRT) across all three time points. Moreover, peak torque (PT) and peak torque fatigue index (PTFI) showed significant differences between the three times of the day, peaking in the evening. Although we found no interaction between CR and physical fatigue state on selected cognitive parameters at the three times of day, a separate effect of fatigue on cognitive performance was identified. Additionally, physical parameters exhibited peak values occurring in the evening hours. Future research should further explore underlying mechanisms that potentially influence cognitive performance at different times of the day.
... There are numerous studies that have demonstrated physiological processes in the human body, such as heart rate, hormonal patterns, core body temperature, and blood pressure all exhibit robust circadian rhythms [22][23][24][25][26][27][28][29][30]. Further, evidence supports that these daily oscillations are not acute responses to the immediate environment but are regulated by intrinsic circadian clocks. ...
... For example, hormonal levels of cortisol and melatonin, heart rate, blood pressure, and body temperature all exhibit well defined circadian variation. To this end, it has long been established that typically both cortisol [31] and body temperature [25,32] are at peak levels during the mid-afternoon/evening, while levels of melatonin display higher values during the nocturnal period preceding the transition to sleep [33]. ...
... For example, measures of power output, strength, endurance capacity, and maximal uptake of VO 2 have all been shown to be elevated during the evening compared to the morning [21,[34][35][36][37][38]. This evening superiority of muscle force production and power output are also displayed regardless of the muscle group measured [25,29]. Short-term maximal power output (often referred to as anaerobic performance) i.e., activities lasting less than 6 s have previously been shown to peak between 17:00 to 19:00 h [39,40]. ...
... La chronobiologie est la science qui s'intéresse à la variation périodique des (Atkinson and Reilly, 1996). ...
... Adaptée de Reilly et al. (2009). Par la suite, d'autres fonctions ont été révélées comme suivant également un rythme circadien (Atkinson and Reilly, 1996), comme par exemple la sécrétion hormonale de la mélatonine et du cortisol. La mélatonine, aussi nommée hormone du sommeil, présente une acrophase pendant la nuit et une chute de sa concentration jusqu'au matin. ...
... Outre son influence sur différentes fonctions de notre organisme, nous savons depuis plusieurs années que les rythmes circadiens ont également un impact sur nos performances, qu'elles soient cognitives (Carrier and Monk, 2000;Wright et al., 2012), ou motrices (Atkinson and Reilly, 1996;Drust et al., 2005). ...
While the time of day significantly affects motor and mental performance, its influence on motor learning has not yet been elucidated. In this thesis, we conducted a series of experiments using a finger-tapping task to investigate the effects of time of day on two processes of motor learning: acquisition (i.e. skill improvement immediately after a training-session) and consolidation (i.e. skill retention after the passage of time and/or a night of sleep).
In the 1rt study, we showed that the time of day influenced the consolidation, but not the acquisition. Specifically, while we observed deterioration and stabilization of skill 24 hours after morning and afternoon training, respectively, we found a better consolidation 24 hours after evening training with a subsequent improvement in skill. These results highlight the crucial role of sleep in consolidating motor skills acquired beforehand.
In the 2nd study, comprising four experiments, we explored the question of the fragility of memory after morning training. Our initial results showed that memory was more fragile in the morning than in the afternoon, with deterioration occurring within 5 hours of practice only during morning training. In the subsequent two experiments, we investigated two types of interference, motor and cognitive, and found that memory was more susceptible to motor interference in the morning. Furthermore, the deterioration in performance seemed to arise from a conflict between the declarative and procedural memory systems required for our task. Additionally, we provided neurophysiological evidence for these different consolidations by demonstrating a different modulation of corticospinal excitability immediately post-practice, which varied depending on the time of day.
In the 3rd study, we emphasized the importance of daily activity in consolidation. We observed that engaging in motor activity before morning practice prevented performance deterioration during the day, whereas remaining inactive until afternoon practice resulted in worsened performance. We suggested that, while sleep is advantageous for the consolidation of previously acquired skills, it may hinder the consolidation of subsequent learning due to the inactivity it promotes.
In our final 4th study, we showed that the time of day also influenced consolidation following a mental practice. Although the acquisition and consolidation processes differ between physical and mental practice, we found that consolidation was also better in the afternoon than in the morning.
Overall, the results of this thesis underscore the importance of considering the time of day and the activities undertaken before learning when designing optimal training programs and rehabilitation protocols.
... Participants woke at 06:30 h to come into the laboratory at 07:00 h for both conditions having fasted and then completed the sleep questionnaires. If they were in the evening condition, they then were able to and were asked not to consume food 4 h before the start of the evening session (Atkinson and Reilly 1996). In all sessions the participants retired at around 22:30 h and rose around 06:30 h, having had a text message which they had to respond to. ...
... It has been previously suggested that diurnal variations related to exercise are generally larger in amplitude in physically fit than sedentary individuals (Atkinson and Reilly 1996). However, _ VO 2 max is a stable function regardless of time of day (Drust et al. 2005) and highly trained cyclists are used to training at different times of day and at intensities close to 100% _ VO 2 max. ...
... Like others, we reported lower ratings of the mood state fatigue and higher rating of vigour values in the evening compared to the morning condition (Hill and Smith 1991;Brotherton et al. 2019). Importantly, the diurnal variation in resting Tr and Tsk temperature values (0.48 and 0.26 °C), which has been well established by previous research was also observed (Atkinson and Reilly 1996;Edwards et al. 2002;Waterhouse et al. 2005a). ...
... Initially, the effects of circadian rhythms on daily performance were studied more in the field of sports, where research showed significant individual differences in athletes' sleepwake habits, sometimes misconstrued as laziness by coaches. Although an optimal chronotype for sports performance is yet to be identified, a training programme that does not align with an athlete's biological clock may be difficult to adhere to [1]. E. Teng et al. highlight that enhancing sleep qualities, especially an athlete's view of sleep, can significantly impact sports outcomes [23]. ...
... Endogenous and exogenous factors Circadian rhythms are not fully dependent upon exogenous factors, but also have an "endogenous component". Numerous physiological circadian rhythms are endogenously regulated during rest and continue while a person is shielded from external changes [1]. A synchroniser or "time donor" is a factor of the exogenous environment, a living organism whose periodic variations can modulate the biological rhythms of this organism. ...
... Research studies, exploring the influence of circadian rhythms on performance, need meticulous planning to account for the effects of consecutive fatigue and to reduce sleep disruptions. The degree of test-retest repeatability of the measuring apparatus has a significant impact on rhythmicity identification in performance variables [1]. ...
Introduction. Biological cycles exist across diverse time spans. Circadian rhythms are the most thoroughly examined and significantly influence individuals. These rhythms in physiological measures are affected by cyclical variations in human actions and surroundings over a 24-hour duration.
Aim. The present research aims to analyse the association of biorhythm factors with performance in students considering research in the field of chronobiology in relation to the educational field.
Research methodology and methods. The present systematic review summarises 34 records treating sleep quality, lifestyle, and circadian preferences in their association with the academic, physical, and cognitive performance of students during their daily life; using a PRISMA model.
Results. The current review paper has cited numerous studies that confirm the significant impact of sleep and circadian preference on a student’s academic, psychomotor, and cognitive performance. These two factors play a crucial role in the rhythmicity of a student’s life.
Scientific novelty. This study introduces a novel interdisciplinary method that applies findings from the study of biological rhythms to education, revealing how these rhythms affect student learning and performance. By merging chronobiology with educational theory, it opens new research paths and enhances our understanding of the relationship between students’ circadian rhythms and their academic, cognitive and physical results, representing a significant progression in how the field of education is linked with chronopsychology.
Practical significance. Educational professionals can use the results obtained to gain a deeper insight into how chronobiological factors may affect student performance, thereby enhancing their comprehension of student productivity and potentially identifying more efficient ways to improve it.
... For example, the amount of training 10,11 , the distribution of rest periods during a training session 12,13 , or the variation of skills within a single training session 14,15 have been the topic of dedicated investigations. Astonishingly, although several studies have shown that motor and mental performances fluctuate across the day, following a circadian basis (∼24 h) [16][17][18] , the search for the optimal time-of-day for motor learning has not yet retained great attention. Daily variations were observed for maximal voluntary contractions 19 , spontaneous motor tempo 20 , speed/accuracy tradeoff of actual and mental movements 21 , handwriting 22 , and tennis service 23 . ...
... We measured skill acquisition, namely the enhancement in skill performance during and immediately after practice, and skill consolidation, i.e., the enhancement in skill performance 24 h later. Following the time-of-day literature 16 , we hypothesized that skill acquisition and consolidation should be better in the afternoon compared to the morning. We also motivated this premise by neurophysiological findings showing that physiological mechanisms are modulated throughout the day, such as the cortisol diurnal secretion related to LTP-like plasticity in the motor cortex 31 and the degree of hippocampus activation 32,33 , associated with consolidation 34,35 . ...
... These results may be surprising since clear influences of the time-of-day on behavioral and neural processes have been described 16,18 . For instance, the maximal voluntary contraction 19 , speed/accuracy tradeoff of actual and mental movements 21 , handwriting 22 , and badminton serve accuracy 40 fluctuate through the day. ...
We investigated the influence of the time-of-day and sleep on skill acquisition (i.e., skill improvement immediately after a training-session) and consolidation (i.e., skill retention after a time interval including sleep). Three groups were trained at 10 a.m. (G10 am ), 3 p.m. (G3 pm ), or 8 p.m. (G8 pm ) on a finger-tapping task. We recorded the skill (i.e., the ratio between movement duration and accuracy) before and immediately after the training to evaluate acquisition, and after 24 h to measure consolidation. We did not observe any difference in acquisition according to the time of the day. Interestingly, we found a performance improvement 24 h after the evening training (G8 pm ), while the morning (G10 am ) and the afternoon (G3 pm ) groups deteriorated and stabilized their performance, respectively. Furthermore, two control experiments (G8 awake and G8 sleep ) supported the idea that a night of sleep contributes to the skill consolidation of the evening group. These results show a consolidation when the training is carried out in the evening, close to sleep, and forgetting when the training is carried out in the morning, away from sleep. This finding may have an important impact on the planning of training programs in sports, clinical, or experimental domains.
... These variations are partly caused by the influence of the endogenous circadian system, causing endogenous circadian oscillations in biological processes following a cycle of approximately 24 h, i.e., that persist in the absence of environmental and behavioral cycles such as the dark/light, sleep/wake, and fasting/eating cycles [9,12,[15][16][17]. Several reviews have discussed evidence for diurnal variations for many performance-related outcomes, with acrophases in the afternoon and evening [18][19][20][21][22][23][24][25][26][27][28][29]. A recent meta-analysis, for example, provided statistical evidence that mean power output in the 30-s Wingate test, jump height, as well as handgrip strength is higher in the late afternoon and early evening as compared to the morning [24]. ...
... The underlying mechanisms causing within-day and interindividual variations in peak performance are still unclear and may be due to myriad factors such as habitual exercise time, individual chronotype, sleep, food and caffeine intake, environmental conditions, and the endogenous circadian system [10]. Several reviews that investigated diurnal variations in maximum performance concluded that the time of day when the peak performance is achieved may also be the ideal timing for exercise [18][19][20][21]29], with further reviews suggesting that the time of exercise training should coincide with the time of competition to achieve optimal performance improvements [22,25,30]. Observational studies found associations between the time of day of exercise and cardiorespiratory fitness [31], as well as the risk of coronary heart disease [31], obesity [32], prostate cancer, and breast cancer [33] suggesting that timing of exercise in fact might matter for improving performance and health outcomes in the long term. ...
... In addition, means, standard deviations, and other statistics were extracted for all outcomes. The details for all the extracted data are presented in Additional file 1: Table S1 (see pages [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. To estimate data from graphs for all studies for which the required data were not provided in tables or texts, the online tool web plot digitizer (https:// autom eris. ...
Background
Current recommendations for physical exercise include information about the frequency, intensity, type, and duration of exercise. However, to date, there are no recommendations on what time of day one should exercise. The aim was to perform a systematic review with meta-analysis to investigate if the time of day of exercise training in intervention studies influences the degree of improvements in physical performance or health-related outcomes.
Methods
The databases EMBASE, PubMed, Cochrane Library, and SPORTDiscus were searched from inception to January 2023. Eligibility criteria were that the studies conducted structured endurance and/or strength training with a minimum of two exercise sessions per week for at least 2 weeks and compared exercise training between at least two different times of the day using a randomized crossover or parallel group design.
Results
From 14,125 screened articles, 26 articles were included in the systematic review of which seven were also included in the meta-analyses. Both the qualitative synthesis and the quantitative synthesis (i.e., meta-analysis) provide little evidence for or against the hypothesis that training at a specific time of day leads to more improvements in performance-related or health-related outcomes compared to other times. There was some evidence that there is a benefit when training and testing occur at the same time of day, mainly for performance-related outcomes. Overall, the risk of bias in most studies was high.
Conclusions
The current state of research provides evidence neither for nor against a specific time of the day being more beneficial, but provides evidence for larger effects when there is congruency between training and testing times. This review provides recommendations to improve the design and execution of future studies on this topic.
Registration: PROSPERO (CRD42021246468).
... Visual and vestibular inputs to the IGL, which project to the SCN, are strongly anatomically entangled [92]. Consequently, the effect of activity onset on the sleep/wake cycle in rats [145] and physical activity on circadian rhythm amplitude and phase in humans [77,79,149], which were previously explained by endogenous changes [150], might be partially mediated by the vestibular sense organ, enhancing the stabilization and precision of both external and internal entrainment. Moreover, vestibular stimulation is increasingly used to treat disorders of the sleep-wake rhythm [151][152][153]. ...
... Schematic representation of vestibulo hypothalamic connections.T. Martin et al.SleepMedicine 126 (2025) [148][149][150][151][152][153][154][155][156][157][158] ...
This review attempts to analyze the relationship between the vestibular system and the circadian timing system. The activity of the biological clock allows an organism to optimally perform its tasks throughout the nychtemeron. To achieve this, the biological clock is subjected to exogenous factors that entrain it to a 24h period. While the most powerful synchronizer is the light-dark cycle produced by the Earth’s rotation, research has led to the hypothesis of the vestibular system as a possible non-photic time cue used to entrain circadian rhythms. Demonstrated neuroanatomical pathways between vestibular nuclei and suprachiasmatic nuclei could transmit this message. Moreover, functional evidence in both humans and animals has shown that vestibular disruption or stimulation may lead to changes in circadian rhythms characteristics. Vestibular stimulations could be considered to act synergistically with other synchronizers, such as light, to ensure the entrainment of biological rhythms over the 24-h reference period.
... Such pre-game sessions, consisting in practicing technical and tactical drills for ∼30-45 min in the game-day morning, should be considered as a separate concept from warm-ups (1). The potential effects of morning skate are believed to be related to chronobiology (2), neuromuscular delayed potentiation (3,4) or simply psychological behavior (5). However, it remains unknown whether the addition and the repetition of such sessions in a dense competitive calendar (e.g., 35 morning skate within the 98 on-ice training sessions and 76 matches performed over 28 weeks in the NHL regular season) is valuable. ...
... In addition, consideration is required for exogenous factors such as jet lag and consecutive fatigue and sleep disturbance resulting from the extensive travel schedule of NHL players, for instance, which often involves multiple cross-continental flights and back-to-back games in different time zones that can desynchronize the circadian rhythm and consequently the endogenous body-clock Brocherie and Perez 10.3389/fspor.2023.1284613 Frontiers in Sports and Active Living component (2). Because such circadian misalignment, regardless of travel direction, affects NHL players' performance (13), considering players' chronotype (i.e., "larks" or morning types have preference for morning activities, while "owls" or evening types prefer afternoon activities) (38,39) and individual magnitude in diurnal variation (40) would be recommended, in addition to fatigue monitoring, before suggesting additional morning skate or recovery processes and their optimal timing. ...
... The study was conducted over two weeks, during an official competitive soccer season (on March). To minimize circadian rhythm effects, all sessions were held in the evenings in the same temperature and humidity ranges [38,39]. Before definitive testing sessions, all subjects completed a 2-week familiarization period with the test, to minimize the potential learning effect, which could confound true study effects. ...
... The study was conducted over two weeks, during an official competitive soccer son (on March). To minimize circadian rhythm effects, all sessions were held in the nings in the same temperature and humidity ranges [38,39]. Before definitive testing sions, all subjects completed a 2-week familiarization period with the test, to minimiz potential learning effect, which could confound true study effects. ...
Background:
The ability to rapidly change direction while sprinting is a desirable athletic skill in soccer. Enhancing change of direction (COD) performance depends almost exclusively on specific training, with stretching traditionally considered one such intervention. However, the comparative impact of diverse stretching methods on COD in soccer players remains an area of interest. Therefore, this study aimed to compare the effects of different stretching methods on COD ability in soccer players.
Methods:
Twelve male soccer players playing in the national championship football division II (age: 16.3 ± 0.3 years, height: 1.81 ± 0.10 m, body mass: 67.7 ± 7.2 kg) were tested for COD performance (i.e., Illinois agility test) after (1) control condition (20 min general warm-up without stretching), (2) static stretching, (3) dynamic stretching, (4) combined static-dynamic stretching, and (5) combined dynamic-static stretching. The duration of stretching intervention was approximately 6 min for static and dynamic stretching and 12 min for both the combined stretching conditions. The experimental sessions were separated by 72 h.
Results:
COD improved after dynamic stretching when compared to any other condition (p: 0.03-0.002; ηp2: 0.56-0.73), except for the control condition (p = 0.146; ηp2 = 0.18). In contrast, static stretching induced a detrimental effect on COD when compared only to the dynamic stretching condition (p < 0.01; ES = 1.35).
Conclusion:
Dynamic stretching exercises used by male soccer players in the warm-up improved COD. Other forms of stretching exercises, particularly static stretching, negatively impacted the COD performance. Therefore, coaches can consider integrating dynamic stretching protocols tailored to the athletes' specific needs. Moreover, extending the investigation to encompass a wider range of athletes, including different age groups and genders, would enhance the applicability and generalization of the findings.
... Both cognitive and motor performance exhibit circadian variations [3,9,10]. Attentional levels are generally low in the early morning and reach their highest levels around midafternoon [11], while most components of exercise performance peak in the early evening [12]. Individual differences in the entrainment of circadian clocks to the rhythmic environment are often referred to as "chronotypes", with early "larks" and late "owls" at the extremes of a normal distribution [13]. ...
Time-of-day and individual circadian variability influence cognitive performance, with later chronotypes being most compromised earlier in the day. On the other hand, moderate-intensity exercise has been shown to enhance cognitive function. We sought to evaluate the interplay among circadian rhythms, exercise, and cognitive performance in 22 students from the Uruguayan National Dance School, a population previously characterized as late chronotypes, attending a demanding morning schedule. We assessed sleep habits and physical activity patterns using self-report questionnaires and actigraphy. Before and after morning training, participants completed a psychomotor vigilance task (PVT) and a visual Stroop task (congruent and incongruent). The reaction speeds were lower early in the morning than at noon for all these tasks. We also found (1) a positive correlation between weekend sleep duration and PVT performance before training but not after; (2) a negative correlation between individual circadian phase and Stroop performance for both congruent and incongruent conditions after training but not before; and (3) a better Stroop performance after training for both congruent and incongruent conditions in dancers who engaged longer moderate-intensity exercise during training. Our findings suggest that regular morning training might help mitigate cognitive impairments experienced by dancers with later chronotypes in challenging morning scenarios.
... Further the results were also in line with the Atkinson and Reilly (1996) discussed circadian variant in sports activities and Overall performance. ...
For this study, total of 26 (13 male and 13 female) subjects were selected from the Department of Physical Education, Central University of Kashmir, age ranged between 23 to 27 years. Non-Probability sampling such as purposive sampling was used in the present study. In the present study chronotype was selected as the Independent Variable whereas Speed, Agility and Lower body explosive strength was considered as the dependent variables. Chronotype is understood to reflect a spectrum of behaviors ranging from an extreme preference for morning activity to an extreme preference for evening activity. Horneostberg, (1976) morning - evening question was used to find out the chronotype of the athletes. All the tests were conducted and administered at different times in a day. i.e., morning from 9.30 AM to 10:30 AM and evening between 03:00 pm to 04:00 pm. The obtained data was analyzed by applying the descriptive statistics and paired “t” were worked out and the results have been presented in different tables. . Therefore, it was concluded that mean differences in the explosive strength and agility in morning and evening was statistically significant and it was also concluded that mean differences in the morning 50m sprint and evening 50m sprint were not statistically significant.
... Before each time trial, participants were asked to refrain from strenuous exercise (24 hours), alcohol (24 hours), caffeine (12 hours), and food (2 hours) [28]. ...
The purpose of this study was to determine the effective warm-up protocol using an added respiratory dead space (ARDS) 1200 ml volume mask to determine hypercapnic conditions, on the swimming velocity of the 50 m time trial front crawl. Eight male members of the university swimming team, aged 19–25, performed three different warm-up protocols: 1) standardized warm-up in water (WUCON); 2) hypercapnic warm-up in water (WUARDS); 3) hypercapnic a 20-minute transition phase on land, between warm-up in water and swimming test (RE-WUARDS). The three warm-up protocols were implemented in random order every 7th day. After each protocol, the 50 m time trial front crawl swimming (swimming test) was performed. The fastest time trial swimming of 50 m front crawl was achieved after the hypercapnic transition phase (RE-WUARDS) protocol and was 27.5 ± 1.6 seconds, 1.2% faster than hypercapnic warm-up protocol (p = 0.01). This result was confirmed by a higher swimming average speed of the exercise test after RE-WUARDS compared to WUARDS (p = 0.01). The use of ARDS provoked a state of tolerable hypercapnia (obtaining carbon dioxide concentration in arterialized blood pCO2 > 45 mmHg) achieving a post-warm-up of WUARDS value 49.7 ± 5.9 mmHg (compared to the control condition which was a statistically significant difference p = 0.02) and before time trial RE-WUARDS 45.7 ± 2.1 mmHg (p = 0.01 compared to WUCON). After breathing through the 1200 ml ARDS mask during the 20-minute re-warm-up phase, there was a trend of faster time trial among participants compared to the control condition, and statistically significantly faster times compared to WUARDS, indicating that further study is appropriate to verify the efficacy of the proposed method to improve swimming efficiency.
... In team sport athletes, the coordination of muscle recruitment patterns and the control of movements through proprioceptive feedback reflect the efficacy of the neuromuscular system in initiating and directing specific sports actions that determine performance (1,2). Several aspects could impact neuromuscular performance including nutritional status (3), hormonal fluctuations (4), muscle fiber typology (5), or time-of-day when training/competitions are developed (6). Referring to the effect of time-of-day, it is worth mentioning the last years exponential increase in the number of scientific investigations that analyzed their impact on neuromuscular performance despite limited evidence in professional and semiprofessional athletes can be found (7). ...
Influence of time-of-day on neuromuscular performance in team sport athletes: a systematic review and meta-analysis. Introduction: Although circadian rhythms have been shown to influence some neuromuscular performance tasks, the time-of-day effect on team sports performance athletes remains equivocal. This study aimed to examine the existing evidence concerning diurnal variations in neuromuscular performance in professional and semi-professional team sports athletes using a meta-analytic approach. Methods: A literature search was conducted through three different databases: PubMed, SportDiscus and Web of Science. Article selection was made based on the following inclusion criteria: team sports athletes, professional or semi-professional athletes, neuromuscular performance, testing protocols and time-of-day testing times. Neuromuscular performance parameters such vertical jump capacity (i.e., squat and countermovement jump), agility and isometric strength were included in the analysis. Testing protocols that specifically assessed these parameters across morning (AM) and late afternoon/evening (PM) periods were considered were extracted from the selected studies. Results: Ten studies met the inclusion criteria for qualitative synthesis and five for quantitative synthesis. Meta-analysis indicated lower countermovement jump in the AM compared to with PM (mean difference, −1.44; 95% CI −2.80 to −0.08; p = 0.04) and higher agility performance (mean difference 0.42; 95% CI 0.09-0.74; p = 0.01) in PM comparing with AM. No differences were reported in isometric strength and squat jump performance (p > 0.05). Conclusion: Neuromuscular performance is higher in the late afternoon or early evening compared to morning schedules in team sport athletes. Hence, time-of-day variations need to be considered when evaluating neuromuscular performance in professional and semi-professional team sports athletes.
... Both cognitive and motor performance exhibit circadian variations [3,9,10]. Attentional levels are generally low in the early morning and reach highest levels around mid-afternoon [11], while most components of exercise performance peaks in the early evening [12]. Individual differences in the entrainment of circadian clocks to the rhythmic environment are often referred to as ʹʹchronotypesʹʹ, with early ʹʹlarksʹʹ and late ʹʹowlsʹʹ at the extremes of a normal distribution [13]. ...
Time-of-day and individual circadian variability influence cognitive performance, with later chronotypes being most compromised earlier in the day. On the other hand, moderate-intensity exercise has been shown to enhance cognitive function. We sought to evaluate the interplay between circadian rhythms, exercise, and cognitive performance in 22 students from the Uruguayan National Dance School, a population previously characterized as late chronotypes, attending a demanding morning schedule. We assessed sleep habits and physical activity patterns using self-report questionnaires and actigraphy. Before and after morning training, participants completed a psychomotor vigilance task (PVT) and a visual Stroop task (congruent and incongruent). The reaction speeds were lower early in the morning than at noon for all these tasks. We also found 1) a positive correlation between weekend sleep duration and PVT performance before training but not after; 2) a negative correlation between individual circadian phase and Stroop performance for both congruent and incongruent conditions after training but not before; and 3) a better Stroop performance after training for both congruent and incongruent conditions in dancers who engaged longer moderate-intensity exercise during training. Our findings suggest that regular morning training might help mitigate cognitive impairments experienced by dancers with later chronotypes in challenging morning scenarios.
... All tests were conducted with in-water starts and at the same time of the day to avoid circadian variations. 20 Swimming speed of the first 400-m step was set at 80% of the 400-m freestyle seasonal best and subsequently increased by 3% per step. The 400-m times performed (in seconds) were measured using a stopwatch (FINIS 3X-300M, FINIS, Inc) by an expert swimming researcher. ...
Purpose : The assessment of lactate threshold (LT) and its relationship to open-water (OW) performance is crucial. This study aimed (1) to analyze LT in world-class OW swimmers, (2) to compare swimming speed at LT (SS LT ) and 4 mmol·L ⁻¹ of blood lactate concentration ([La ⁻ ]; SS 4 ), and (3) to examine the relationships between SS LT and swimming performance. Methods : Twenty world-class and elite (11 male, 26.4 [3.0] y; 9 female, 25.8 [3.6] y) OW swimmers voluntarily participated. A total of 46 (29 male and 17 female) intermittent incremental tests (7 × 400 m) conducted in a 50-m pool were analyzed. Seasonal best performances on 400-, 800-, and 1500-m and 10-km OW swimming events were obtained. Results : The SS LT was 1.62 (0.02) (3.8 [1.0] mmol·L ⁻¹ ) and 1.46 (0.04) m·s ⁻¹ (3.0 [0.7] mmol·L ⁻¹ ) in males and females, respectively, which corresponded to 97% of the peak speed reached in the tests. There were no differences ( P = .148) between SS LT and SS 4 in males; however, SS LT was lower ( P = .019) than SS 4 in females. The SS LT was negatively correlated with swimming performance, with the exception of 10-km OW and 400-m times in males and females, respectively. Conclusions : World-class and elite OW swimmers exhibited a greatly developed aerobic capacity with LT close to their maximum speed. The SS 4 could be used as an approximation to SS LT in males but overestimates true aerobic capacity in females. LT is a useful tool for assessing performance, as OW swimmers with higher SS LT showed better swimming performance.
... For example, athletes often exhibit increased strength, power, and endurance in the afternoon and evening compared to early morning [12]. More world records are broken by athletes competing in the early evening, even when controlling for environmental conditions and scheduling biases [13]. Disruptions in circadian rhythms can also harm athletic performance. ...
Chrono-medicine considers circadian biology in disease management, including combined lifestyle and medicine interventions. Exercise and nutritional interventions are well-known for their efficacy in managing Type 2 Diabetes, and metformin remains a widely used pharmacological agent. However, metformin may reduce exercise capacity and interfere with skeletal muscle adaptations, creating barriers to exercise adherence. Research into optimising the timing of exercise has shown promise, particularly for glycaemic management in people with Type 2 Diabetes. Aligning exercise timing with circadian rhythms and nutritional intake may maximise benefits. Nutritional timing also plays a crucial role in glycaemic control. Recent research suggests that not only what we eat but when we eat significantly impacts glycaemic control, with strategies like time-restricted feeding (TRF) showing promise in reducing caloric intake, improving glycaemic regulation, and enhancing overall metabolic health. These findings suggest that meal timing could be an important adjunct to traditional dietary and exercise approaches in managing diabetes and related metabolic disorders. When taking a holistic view of Diabetes management and the diurnal environment, one must also consider the circadian biology of medicines. Metformin has a circadian profile in plasma, and our recent study suggests that morning exercise combined with pre-breakfast metformin intake reduces glycaemia more effectively than post-breakfast intake. In this review, we aim to explore the integration of circadian biology into Type 2 Diabetes management by examining the timing of exercise, nutrition, and medication. In conclusion, chrono-medicine offers a promising, cost-effective strategy for managing Type 2 Diabetes. Integrating precision timing of exercise, nutrition, and medication into treatment plans requires considering the entire diurnal environment, including lifestyle and occupational factors, to develop comprehensive, evidence-based healthcare strategies.
... Sirkadiyen ritim ve uykunun önemi sorgulanmakta, insan sağlığı için sedanter yaşamda kalitesiz uykunun sonuçları bilinmekte iken, elit sporcuların da performanslarını etkilemektedir. Antrenmanın en basit tanımı ile yüklenme dinlenme ilişkisi olarak düşündüğümüzde, dinlenmenin uyku kalitesi ile yüksek ilişkili olduğu bilinmekte olup bu konuda yapılmış birçok çalışma vardır (Atkinson & Reilly, 1996;Boone, Gordon-Larsen, Adair, & Popkin, 2007;Doherty, Madigan, Warrington, & Ellis, 2019;Golem, Martin-Biggers, Koenings, Davis, & Byrd-Bredbenner, 2014;Hynynen, Uusitalo, Konttinen, & Rusko, 2006). Olimpiyat hedefli performans sporcularının boş zamanlarını değerlendirme amaçlı tercih ettikleri dijital oyunla uyku kalite düzeylerinin belirlenmesi için bu çalışma yapılmıştır. ...
... On the whole, measures of both strength and endurance performance tend to be lower in early morning and higher in the afternoon/evening. [4][5][6][7][8][9][10][11][12][13][14] While a number of factors have been proposed to underlie these performance impacting effects of time-of-day, including body temper ature , 15 , 16 motor unit recruitment, [17][18][19] and meal timing/muscle glycogen status, 20 , 21 an emphasized point in the field is that variation in exercise performance is due to circadian fluctuations in the intrinsic properties of skeletal muscle . 13 In contr ast to these data, recent work found that the maximal intrinsic for ce-gener ating capacity of the mouse extensor digitorum longus (EDL) is not different between 2 different times of the light phase (ie, zeitgeber time [ZT] ZT1 and ZT9) 22 (personal communication with Day anidhi S , Kahn RE, and Lieber RL). ...
A growing body of data suggests that skeletal muscle contractile function and glucose metabolism vary by time-of-day, with chronobiological effects on intrinsic skeletal muscle properties being proposed as the underlying mediator. However, no studies have directly investigated intrinsic contractile function or glucose metabolism in skeletal muscle over a 24 h circadian cycle. To address this, we assessed intrinsic contractile function and endurance, as well as contraction-stimulated glucose uptake, in isolated extensor digitorum longus and soleus from mice at four times-of-day (zeitgeber times 1, 7, 13, 19). Significantly, though both muscles demonstrated circadian-related changes in gene expression, there were no differences between the four time points in intrinsic contractile function, endurance, and contraction-stimulated glucose uptake, regardless of sex. Overall, these results suggest that time-of-day variation in exercise performance and the glycemia-reducing benefits of exercise are not due to chronobiological effects on intrinsic muscle function or contraction-stimulated glucose uptake.
... In that study, reduced HR and Bla responses were observed in the second session of lowintensity training performed on the same day. The mechanisms underlying the reduced HR response in the second session of DOUBLE in our study may involve circadian variations ("time-ofday effects") (Atkinson & Reilly, 1996;Chtourou & Souissi, 2012) and/or "preconditioning effects" from the first session (Kilduff et al., 2013). Additionally, the decreased Bla and BG levels from the first to second session of DOUBLE could be attributed to glycogen depletion and reduced CHO availability (Bartlett et al., 2015), despite the relatively short session duration and the provision of large amounts of exogenous CHO. ...
Purpose
To compare acute physiological responses and perceived training stress between one long and two short time- and intensity-matched sessions of moderate-intensity training in endurance athletes.
Methods
Fourteen male endurance athletes (VO2max: 69.2 ± 4.2 mL·min⁻¹·kg⁻¹) performed one 6 × 10-min interval session (SINGLE) and two 3 × 10-min interval sessions interspersed with 6.5 h recovery (DOUBLE) of moderate-intensity training on two separate days, while running in the laboratory, using a counterbalanced cross-over trial. The two training days were separated into a first part/session (interval stage 1–3) and second part/session (interval stage 4–6). Respiratory variables, heart rate (HR), blood lactate concentrations (BLa), and rating of perceived exertion (RPE) were collected during sessions, whereas supine heart rate (HR) was assessed in a 60-min recovery period following sessions. Measures of perceived training stress (1–10) were assessed in the morning of the subsequent day.
Results
HR, Bla, and RPE increased in the second compared to first part of SINGLE (168 ± 7 vs. 173 ± 7 bpm, 2.60 ± 0.75 vs. 3.01 ± 0.81 mmol·L⁻¹, and 13.4 ± 1.0 vs. 14.8 ± 1.1-point, respectively, all p < 0.05). HR and Bla decreased in the second compared to first session of DOUBLE (171 ± 9 vs. 166 ± 9 bpm and 2.72 ± 0.96 vs. 2.14 ± 0.65 mmol·L⁻¹, respectively, both p < 0.05). SINGLE revealed higher supine HR in the recovery period following sessions (65.4 ± 2.5 vs. 60.7 ± 2.5 bpm p < 0.05), session RPE (sRPE, 7.0 ± 1.0 vs. 6.0 ± 1.3-point, p = .001) and sRPE training load (929 ± 112 vs. 743 ± 98, p < 0.001) compared to DOUBLE. In the subsequent morning, increased levels of perceived fatigue and muscle soreness were observed following SINGLE compared to DOUBLE (7.0 ± 2.5 vs. 8.0 ± 1.0-point, p = .049 and 6.0 ± 2.5 vs. 7.0 ± 2.5-point, p = .002, respectively).
Conclusion
One long moderate-intensity training session was associated with a duration-dependent “drift” in physiological responses compared to two short time- and intensity-matched sessions, thereby suggesting a higher overall training stimulus. Simultaneously, the lower cost of the two shorter sessions indicates that such organization could allow more accumulated time at this intensity. Overall, these findings serve as a starting point to better understand the pros and cons of organizing moderate-intensity training as one long versus shorter sessions performed more frequently (e.g., as “double threshold training”) in endurance athletes.
... The sequence order of the swimming conditions was randomly assigned for each group (Figure 1). Both tests were conducted at the same time of the day to avoid circadian variations [15]. The average and maximum total weekly training time (i.e., across all three disciplines) were 15.8 ± 2.7 and 26.8 ± 3.2 h, respectively. ...
This study aimed to compare performance, kinematic, and physiological variables between open water and pool swimming conditions in elite triathletes and to examine the associations between conditions on these variables. Fourteen elite triathletes (10 males and 4 females [23.4 ± 3.8 years]) performed two 1500‐m swimming tests in open water and in a 25‐m pool. Swimming speed, stroke rate (SR), length (SL) and index (SI), heart rate (HR), blood lactate concentrations [La⁻], and end‐exercise oxygen uptake (EEV̇O2) were assessed in both conditions. Lower SL and SI and higher SR were obtained in open water compared with pool swimming (p < 0.05). Moreover, kinematic variables changed as a function of distance in both conditions (p < 0.05). No differences were found in the main physiological variables (HR, [La⁻], and EEV̇O2) between conditions. Respiratory exchange ratio presented lower values in open water than in pool conditions (p < 0.05), while time constant was higher in open water (p = 0.032). The fastest triathletes in open water obtained the best performance in the pool (r = 0.958; p < 0.001). All kinematic variables, HR and peak [La⁻] presented positive associations between conditions (r > 0.6; p < 0.05). Despite physiological invariance, triathletes and coaches should monitor specific open water training to adapt their swimming technique to the competitive environment.
... Desde la perspectiva de la Cronobiología, disciplina encargada de estudiar los ritmos biológicos en los seres vivos, incluyendo los seres humanos, el rendimiento deportivo muestra variaciones a lo largo del día, ya sea por la mañana, tarde o noche (Atkinson y Reilly, 1996;Reilly et al., 1997). ...
... 20 Core body temperature has a nadir at dawn, the moment of greatest propensity to sleep, drowsiness, postural sway, and lower alertness and attention, and greater attention, alertness, and quick response to a stimulus are observed during acrophase. 19,21,22 Thus, CBT may indicate circadian moments of lower motor and cognitive performance and greater sleepiness, 23 which directly impact the risk of accidents. ...
The present study used four different methods to estimate fatigue. Forty-seven volunteers (45 men and 2 women), 41.3 ± 7.5 years old, truck operators for 11.5 ± 6.0 years, were included. All participants accepted the invitation to be included in the study. Actigraphy and core temperature were evaluated. The 5-minute psychomotor vigilance test, the Karolinksa Sleepiness Scale (KSS), and the postural assessment using the Light Sonometer™ (Belo Horizonte, Minas Gerais, Brazil) were performed. Fatigue prediction was performed using the Fatigue Avoidance Scheduling Tool (FAST) program. In response to the Pittsburgh Sleep Quality Index (PSQI), 51.06% had good sleep quality and 48.94% had poor sleep quality with an average efficiency of 81.6%. In response to the actigraphy, workers slept an average of 7.2 hours a day with 93.5% efficiency. The workers' core body temperature (CBT) cosinor analysis showed a preserved circadian curve. Core body temperature showed differences between the 6 hours worked in each shift. Similarly, the light sound level meter showed lower risk scores for fatigue in day shifts. Only the variable of the fastest 10% of the Psychomotor Vigilance Test (PVT) showed worse results, while no significant differences were observed by the KSS. The risk analysis by FAST showed a strong influence of the circadian factor. In conclusion, each method has positive and negative points, and it is up to the evaluator/manager to identify the method that best suits the purpose of the evaluation, as well as the local culture and conditions. We recommend using different methods of risk assessment and management in combination with fatigue prediction by Sonometer as well as carrying out assessments, which enable researchers to estimate performance and fatigue throughout the working day, since these may change over the duration of the working day.
... Recently, a large focus of the field of exercise physiology has been on the effect of time-of-day on exercise capacity and athletic performance. On the whole, measures of both strength and endurance performance tend to be lower in early morning and higher in the afternoon/evening (Atkinson and Reilly, 1996; fatigue are impacted across a 24 h circadian cycle, is unknown. ...
A growing body of data suggests that skeletal muscle contractile function and glucose metabolism vary by time-of-day, with chronobiological effects on intrinsic skeletal muscle properties being proposed as the underlying mediator. However, no studies have directly investigated intrinsic contractile function or glucose metabolism in skeletal muscle over a 24 h circadian cycle. To address this, we assessed intrinsic contractile function and endurance, as well as contraction-stimulated glucose uptake, in isolated extensor digitorum longus and soleus from female mice at four times-of-day (Zeitgeber Times 1, 7, 13, 19). Significantly, while both muscles demonstrated circadian-related changes in gene expression, intrinsic contractile function, endurance, and contraction-stimulated glucose uptake were not different between the four time points. Overall, these results demonstrate that time-of-day variation in exercise performance and the glycemia-reducing benefits of exercise are not due to chronobiological effects on intrinsic muscle function or contraction-stimulated glucose uptake.
Impact statement
Ex vivo testing demonstrates that there is no time-of-day variation in the intrinsic contractile properties of skeletal muscle (including no effect on force production or endurance) or contraction-stimulated glucose uptake.
... To avoid a possible learning effect, swimmers were familiarized with the experimental procedures before the intervention. In both PRE and POST conditions, testing was performed on the same time of the day to avoid possible biases due to circadian variation (Atkinson and Reilly, 1996). Furthermore, swimmers were instructed to refrain from intense exercise and/or vigorous physical activity and to abstain from stimulant beverages consumption 24 h before each testing session. ...
This study aimed to evaluate the effects of a five-week training program on undulatory underwater swimming (UUS) in swimmers and to compare the specific effects prompted by two different training protocols on UUS performance and kinematics. Swimmers (n = 14) were divided into in-water only (WO) (18.61 ± 2.62 years, FINA points: 507 ± 60) and water + dry-land training groups (with conical pulleys) (WD) (18.38 ± 2.67 years, FINA points: 508 ± 83). Three countermovement jumps (CMJ) and three maximal UUS trials were performed before and after a five-week training period. The training program comprised 14 × 30-min sessions. The WO group repeated the same 15-min block twice, while the WD group performed one block of 15 min in the water and the other block on land performing lower limb exercises with conical pulleys. Seven body landmarks were auto-digitalized during UUS by a pre-trained neural network and 21 kinematic variables were calculated. The level of statistical significance was set at p < 0.05. Significant time × group interaction in favour of the WD group was observed for mean vertical toe velocity (p = 0.035, ηp2 = 0.32). The WD group experienced enhancements in mean and maximum underwater velocity, kick frequency, maximum shoulder angular velocity, as well as mean and maximum vertical toe velocity (p < 0.05). The WO group exhibited an enhancement in CMJ height (p < 0.05). In conclusion, UUS performance was improved in adolescent swimmers after five weeks of specific training, only when combining water and conical pulley exercises. Coaches should include dry-land specific lower limb exercises in addition to in-water training to improve UUS performance.
... In sport, adequate sleep is pivotal for the preparation and recovery from training and competition (Fox et al. 2020). From a general standpoint, fundamental biological rhythms regulate the repetitive processes of human life cycles (Atkinson and Reilly 1996). Within this context, continuous unperturbed sleep represents a physiological necessity to preserve normal cognitive and neurobehavioral functions (Maquet 2001;Van Someren et al. 2015;Logan and McClung 2019;Walsh et al. 2020). ...
... The second evaluation session was conducted the day after at the same time of the day to avoid systematic bias due to circadian variation. 20 In addition, swimmers were instructed to maintain their normal dietary patterns as well as to refrain from performing other vigorous exercise for 24 hours before each testing session. Swimmers were verbally encouraged during all the land and in-water tests. ...
Purpose: To explore the association of the load-velocity (L-V) relationship variables and ability to maintain maximal mechanical performance during the prone bench pull exercise with sprint swimming performance and in-water forces. Methods: Eleven competitive adult male swimmers (50-m front crawl World Aquatics points: 488 ± 66, performance level 4) performed one experimental session. The L-V relationship variables (L0 [i.e., maximal theorical load at zero velocity]; v0 [i.e., maximal theorical velocity at zero load] and, Aline [i.e., area under the L-V relationship]) and maximal mechanical maintenance capacity were assessed at the beginning of the session. Afterwards, sprint swimming performance and in-water forces production were tested through a 50-m front crawl all-out trial and 15-s fully-tethered swimming, respectively. Results: Only v0 presented high positive associations with 50-m time and swimming kinematics (r > 0.532; p < 0.046). The L0, v0 and Aline showed very high positive associations with the in-water forces during tethered swimming (r > 0.523; p < 0.049). However, the ability to maintain maximal mechanical performance, assessed by the mean velocity decline during the PBP, was only significant correlated with stroke rate (
r = -0.647; p = 0.016) and stroke index (r = 0.614;p = 0.022). Conclusions: These findings indicate that maximal neuromuscular capacities, especially v0, have a stronger correlation with swimming performance and in-water force production than the ability to maintain maximal mechanical performance in level 4 swimmers.
... For retesting the participants were scheduled at the same time of the day (±1 h) where possible, so that any fluctuations due to diurnal effects were diminished. 34 2.6. Respiratory muscle training | | The THRESHOLD® Inspiratory Muscle Trainer, Respironics, USA was used in this study. ...
Background/objectives
Respiratory muscle training (RMT) was recognized as an effective means to improve respiratory muscle (RM) strength and enhance exercise performance. The purpose of this study was to examine the effect of low-intensity RMT on RM strength, pulmonary function, and performance.
Methods
Fourteen healthy active adults were assigned randomly to either a training or placebo group. The training group completed six weeks of RMT, which consisted of a first week, 1 set of 15 min/d, 5 d/wk at 10–25% of maximal inspiratory pressure (PImax), and the remaining 5 weeks, 2 sets of 15 min/d, 5 d/wk, at 30% PImax. The placebo group followed the same protocol but with almost no additional ventilatory resistance. Measurement of RM strength and endurance, spirometry, and endurance exercise performance were obtained before and after the RMT program.
Results
In the training group, PImax (+14%) and maximal expiratory pressure (PEmax, +27%), forced vital capacity (FVC, +3.6%), maximal oxygen uptake (VO2max, +11%), and time to exhaustion (Tlim90%, +25%) increased significantly from baseline values (P < 0.05). No significant changes were observed in the placebo group. Also, no significant interaction in maximum voluntary ventilation (MVV12), minute ventilation (VE), and respiratory rate (RR) were detected.
Conclusions
These data suggest that low-intensity RMT is an effective tool to improve RM strength, pulmonary elastic properties and endurance exercise performance.
... (18) which correlates with performance (19) and is altered under conditions of sleep deprivation (20). CBT has a nadir at dawn, a moment of greatest: propensity to sleep, drowsiness, postural sway and lower alertness and attention, and during acrophase it presents greater attention, alertness, and quick response to a stimulus (19,21,22). Thus, it may indicate circadian moments of lower motor and cognitive performance and greater sleepiness (23) which directly impact the risk of accidents. ...
... Various factors have been theorized to underpin these time-of-day differences in neuromuscular performance, including athlete chronotype (i.e., expression of circadian rhythmicity, reflecting predispositions toward morningness or eveningness) (Vitale & Weydahl, 2017), scheduling of training sessions and games (Souissi et al., 2002), the time at which performance occurs since entrained awakening (Facer-Childs & Brandstaetter, 2015), and diurnal fluctuations in biochemical markers (e.g., creatine kinase) (Hammouda et al., 2012). However, diurnal fluctuations in core body temperature, with peaks typically occurring in the late afternoon (Atkinson & Reilly, 1996), have also been proposed to contribute to time-of-day differences in neuromuscular performance. In this way, elevated core body temperature has been associated with physiological enhancements to intracellular phosphate concentrations (Martin et al., 1999) as well as myofilament calcium sensitivity and actin-myosin crossbridge cycle kinetics during muscle contraction (Decostre et al., 2005). ...
Purpose: The aim of this study was to determine whether variations in technical and neuromuscular performance occur across different times of the day in basketball players. Methods: Twenty semiprofessional, female basketball players (23 ± 4 years) competing in a second-division national basketball competition completed separate testing batteries in the morning (08:30) and in the afternoon (17:30) in a randomized counterbalanced order. Testing sessions consisted of a free-throw accuracy test to assess technical performance, as well as flexibility (ankle dorsiflexion range-of-motion test), dynamic balance (modified star excursion balance test), vertical jump height (squat jump, countermovement jump with and without arm swing), strength (isometric handgrip), change-of-direction speed (V-cut test), and linear speed (20-m sprint) tests to assess neuromuscular performance. Mechanism variables were also obtained including tympanic temperature, urinary specific gravity, and rating of perceived exertion at each session. Results: Squat jump height (6.7%; p = .001; effect size (ES) = 0.33), countermovement jump height with (4.1%; p = .018; ES = 0.27) and without arm swing (5.9%; p = .007; ES = 0.30), and 20-m sprint time (−1.4%; p = .015; ES = -0.32) were significantly superior in the afternoon compared to morning. Tympanic temperature was significantly higher in the afternoon than morning (1.4%; p < .001; ES = 1.31). In contrast, no significant differences between timepoints were evident for all remaining variables (p > .05; ES = -0.33 to 0.16). Conclusions: Some neuromuscular variables exhibited a time-of-day effect with better jump and sprint performance in the afternoon compared to morning in semiprofessional, female basketball players.
... Estimating core temperature appears to be useful because it has also been used as a circadian marker of physical performance (Reilly and Waterhouse, 2009), motor and cognitive performance (Schmidt et al., 2007), in addition to moments of greater alertness and attention, quicker response to a stimulus, greater muscle strength, greater aerobic and anaerobic power, and increases in flexibility parameters that coincide with core temperature acrophase (Atkinson and Reilly, 1996;Atkinson et al., 2005;Reilly and Edwards, 2007). ...
... Clock-driven oscillations in metabolic regulation, such as glucose metabolism requiring less oxygen consumption, lower heart rate, and lower perceived exertion, have been linked to changes in human exercise performance (late vs. early better) [132]. Although it is not an entirely novel idea, this association between exercise capacity and the molecular clock in competitive and elite sports situations may be helpful when planning to improve training programs and competitions [133]. Strength training studies have demonstrated that an increase in oxidative stress due to exercise causes a response to muscle injury [134]. ...
Objectives
This study was a narrative review of the importance of circadian rhythm (CR), describes the underlying mechanisms of CR in sports performance, emphasizes the reciprocal link between CR, endocrine homeostasis and sex differences, and the unique role of the circadian clock in immune system function and coordination.
Method
As a narrative review study, a comprehensive search was conducted in PubMed, Scopus, and Web of Science (core collection) databases using the keywords “circadian rhythm”, “sports performance”, “hormonal regulation”, “immune system”, and “injury prevention”. Inclusion criteria were studies published in English and peer-reviewed journals until July 2023. Studies that examined the role of CR in sports performance, hormonal status, immune system function, and injury prevention in athletes were selected for review.
Results
CR is followed by almost all physiological and biochemical activities in the human body. In humans, the superchiasmatic nucleus controls many daily biorhythms under solar time, including the sleep-wake cycle. A body of literature indicates that the peak performance of essential indicators of sports performance is primarily in the afternoon hours, and the evening of actions occurs roughly at the peak of core body temperature. Recent studies have demonstrated that the time of day that exercise is performed affects the achievement of good physical performance. This review also shows various biomarkers of cellular damage in weariness and the underlying mechanisms of diurnal fluctuations. According to the clock, CR can be synchronized with photonic and non-photonic stimuli (i.e., temperature, physical activity, and food intake), and feeding patterns and diet changes can affect CR and redox markers. It also emphasizes the reciprocal links between CR and endocrine homeostasis, the specific role of the circadian clock in coordinating immune system function, and the relationship between circadian clocks and sex differences.
Conclusion
The interaction between insufficient sleep and time of day on performance has been established in this study because it is crucial to balance training, recovery, and sleep duration to attain optimal sports performance.
... In order for the athletes to reach their potential, sports staff aims to improve and develop all performance components. It has been demonstrated that athletic performance and the time zones of the day in which this performance is realized, in other words, circadian rhythm are related (5)(6)(7)(8)(9)(10)(11)(12)(13)(14). In studies conducted in different groups, it was found that the power changes between 3% and 21.2% in different time zones of the day (6,9,14). ...
The relationship between the reaction time and the total running time of male (n=407) and female (n=345) athletes competing in the 60-meter wind sprint branch at the world indoor championships between 2006 and 2022 and the competition hour was examined in this study. Statistically significant and negative relationships were found between competition hour and athletes' reaction times, competition hour and athletes' competition result ratings in both genders (rho<0.040; p<0.05). When the subject is examined in terms of the stages of the competitions, no relationship was found for both genders in the final stage while the same relationships were preserved in the semi-final stage. At the qualification stage, a positive relationship was observed between the competition hour and the reaction time in both men (rho=0.25) and women (rho=0.22). In particular, it will be important that the competition time zones in the qualification stage are in similar circadian zones so as not to create a disadvantage among the athletes, and that the competition programs should be prepared by taking the performance-limiting and performance-supporting time zones into account.
... All PF testing was performed in a single session as part of an annual physical fitness assessment which took place at the start of the academic year for freshmen and at the end of the academic year for seniors by trained investigators. Generally, these were all performed at the same time of day to minimize circadian variation in testing [25]. All investigators followed instructions from the same standard instruction manual and were trained by the same lead investigator in this prospective longitudinal study. ...
Dance is physically demanding, requiring physical fitness (PF) that includes upper body, lower body, core fitness, and balance for successful performance. Whether PF changes as dancers advance from when they enter (freshmen) to when they graduate from their collegiate program (seniors) is unclear. We prospectively compared collegiate dancers’ freshman-to-senior PF. We recorded PF in regard to upper body strength endurance (push-ups), core strength endurance (front, left-side, right-side, and extensor plank hold times), lower body power (single leg hop—SLH—distances % height; Leg Symmetry Index: LSI = higher/lower × 100, %), and balance (anterior reach balance, % leg length, LL; LSI balance = higher/lower × 100, %) in 23 female collegiate dancers (freshman age = 18.2 ± 0.6 years). Repeated measures ANOVAs (p ≤ 0.05) were used to compare measures from freshman to senior years. Across their collegiate programs, dancers’ PF remained unchanged. Specifically, their upper body strength endurance push-up numbers (p = 0.93), their core strength endurance plank times (left: p = 0.44, right: p = 0.67, front: p = 0.60, p = 0.22), their SLH distances (left: p = 0.44, right: p = 0.85), and their symmetry (p = 0.16) stayed similar. Also, dancers’ right leg (p = 0.08) and left leg balance (p = 0.06) remained similar, with better balance symmetry (p < 0.001) in seniors. Overall, dancers’ PF did not change across their collegiate programs. Thus, female dancers’ freshman PF may be an adequate baseline reference measure when devising rehabilitation programs and determining readiness-to-return-to-activity post injury.
... All PF testing was performed in a single session as part of an annual physical fitness assessment which took place at the start of the academic year by trained investigators. Generally, these were all performed at the same time of day to minimize circadian variation in testing [28]. All investigators followed instructions from the same standard instruction manual and were trained by the same lead investigator in this prospective longitudinal study. ...
Dance is physically demanding, requiring physical fitness(PF) that includes upper body, lower body, core fitness, and balance for successful performance. Whether PF changes as dancers advance from when they enter(freshmen) to when they graduate from their collegiate program(seniors) is unclear. We prospectively compared collegiate dancers’ freshman-to-senior PF. We recorded PF of the upper body strength-endurance(push-ups, n=number), core strength-endurance(front, left-side, right-side, and extensor plank hold times, s=seconds), lower body power(Single-leg-hop-SLH distances % Height; Leg Symmetry Index: LSI=higher/lower*100, %), and balance(Anterior Reach Balance,%Leg-Length, LL; LSI balance=higher/lower*100, %) in 25 collegiate dancers(23 females, 2 males; freshmen age=18.2±0.6yrs). Paired t-tests(p<.05) compared measures from freshmen-senior years. Across their collegiate programs, dancers’ PF remained unchanged: upper body strength-endurance push-ups numbers(p=.93), core strength-endurance plank times(left:p=.44, right:p = .67, front:p=.60, p=.22), SLH distances(left: p =.44, right:p =.85) and SLH symmetry(p=0.16). Dancers’ right leg balance(p =.08) remained similar, while the left balance(p =.02) improved with better symmetry(p<.001) in senior balance scores. Overall, dancers’ PF did not change across their collegiate programs, except for greater left leg balance scores. Findings suggest that practitioners can use collegiate dancers’ freshmen baseline PF when devising rehabilitation programs and making return to activity decisions post injury throughout their dance programs.
... Es así, que se ha comprobado, que el rendimiento deportivo para casi todas las cualidades físicas (fuerza, potencia, resistencia aeróbica, velocidad de reacción, flexibilidad, etc.) y para todos los tipos de ejercicio (ejercicios anaeróbicos alácticos, lácticos y aeróbicos) es mayor por la tarde que por la mañana (alcanzando el pico de rendimiento cerca de las 18:00), porque dicho rendimiento depende directamente de la temperatura corporal. Esta mejora del rendimiento deportivo con el aumento de la temperatura corporal, se explica por el aumento del flujo sanguíneo a los músculos, aumento de la elasticidad muscular y mayor velocidad de conducción nerviosa (entre otros) obtenidos gracias al aumento de la temperatura del cuerpo (Shellock & Prentice 1985), (Atkinson & Reilly 1996), (Souissi et al. 2002), (Drust et. al. 2005) y (Hayes et. ...
- COMPOSICIÓN LÍUIDA DEL ORGANISMO
- VASOCONSTRICCIÓN Y VASODILATACIÓN
- ESTIMULACIÓN INTRÍNSECA (automatismo)
- ESTIMULACIÓN EXTRÍNSECA
- MECANISMOS DE RETORNO VENOSO AL CORAZÓN
- VOLUMEN Y COMPOSICIÓN DE LA SANGRE
- SISTEMA LINFÁTICO
- MECANISMOS DE PÉRDIDA DE CALOR
- GLÁNDULAS SUDORÍAPARAS Y ACTIVIDAD FÍSICA
- REDISTRIBUCIÓN SANGUÍNEA EN RELACIÓN CON LA TEMPERATURA
CORPORAL
- REDISTRIBUCIÓN SANGUÍNEA EN RELACIÓN CON LA INGESTA DE
ALIMENTOS
- COMPETENCIA DE SANGRE
- TRANSPIRACIÓN Y PÉRDIDA ELECTROLÍTICA
- HUMEDAD, CALOR Y TERMORREGULACIÓN
- FACTORES DE LOS QUE DEPENDE LA SUDORACIÓN
- DESHIDRATACIÓN
- ¿COMO CONOCER EL NIVEL DE HIDRATACIÓN?
- INCONTINENCIA URINARIA AL ESFUERZO
- TRANSTORNOS POR CALOR
- LEY O MECANISMO DE FRANK-STARLING
- IRRIGACIÓN CORONARIA
- MODIFICACIONES DEL VOLUMEN SISTÓLICO DURANTE EL EJERCICIO
- MODIFICACIONES DEL CICLO CARDÍACO CON EL EJERCICIO
- ¿POR QUÉ AUMENTA EL VOLUMEN SISTÓLICO AL REALIZAR
EJERCICIO?
- ALGUNOS CONCEPTOS
- VS, FC Y Q EN REPOSO Y EN EJERCICIO MÁXIMO
- FRECUENCIA CARDÍACA Y SU PROPORCIONALIDAD CON LA
INTENSIDAD DE EJERCICIO
- ¿CÓMO CALCULO LA INTENSIDAD A LA QUE DESEO ENTRENAR?
- FACTORES QUE PUEDEN MODIFICAR LA RESPUESTA DE LA FC ANTE
UN ESFUERZO
- PRESIÓN ARTERIAL Y TENSIÓN ARTERIAL
- MODIFICACIONES DE LA PRESIÓN ARTERIAL DURANTE EL EJERCICIO
- ADAPTACIONES DEL SISTEMA CARDIOVASCULAR ANTE EL EJERCICIO
- PATOLOGÍAS DEL SISTEMA CARDIOVASCULAR Y SU RELACIÓN CON
LA ACTIVIDAD FÍSICA
- ACTIVIDAD FÍSICA EN LA PREVENCIÓN DE ENFERMEDADES CARDIOVASCULARES
Extensive research has demonstrated that shiftwork produces deleterious effects on health because of the desynchrony it induces in the biological clock. The problem is even more crucial for older workers who present, in addition, various decrements in their cognitive functioning, particularly on attention and memory. The present study assessed whether age was related to task complexity as a function of time of day and time-on-task in a rapid rotating work-rest schedule. 24 subjects (12 juniors: 20–30 years and 12 seniors: 50–60 years) performed either a simple task (visual discrimination) or a complex task (descending subtraction) on three different moments of the day simulating the main shifts (morning, evening, and night). Analysis indicated that an age effect was only present on the more complex task, which was demanding in attentional resources and memory load. Seniors had no deficit in performance on the simple task compared to juniors. The effect of time of day was restricted to the simple task for both age groups. However, some differential strategies appear to distinguish juniors and seniors, specifically on accuracy during the night, suggesting that subjects of different ages cope with cognitive tasks in different ways and that perhaps some adverse effects apparently associated with aging could be counteracted by efficient strategies, but not others.
Purpose : To assess the effect of 5-week training-cessation period on performance and load–velocity profile-related variables. Methods : Twenty-four competitive swimmers (15 male and 9 female: 19.2 [3.7] and 17.3 [2.3] y, 50-m front-crawl 550 [70], and 572 [51] World Aquatics points, respectively) performed a 50-m front-crawl all-out swim, a load–velocity profile, and a pull-up test before and after a 5-week off-season period. Kinematic variables, blood lactate concentration, and rating of perceived exertion were monitored during the load–velocity profile tests. Results : Performance was impaired 1.3% for males ( P < .01) and 3.8% for females ( P < .01). Neither anthropometric changes (males r ² = .277, females r ² = .218, P > .05) nor the physical activity performed during the off-season (males r ² = .329, females r ² = .094, P > .05) attenuated performance impairments. While males counteracted the stroke-rate decline ( P < .05) by increasing stroke length ( P < .05) in the majority of the race, females did not, leading to a decline in clean swimming speed ( P < .05). The maximum load at zero velocity decreased ( P < .05) during the load–velocity profile test. In addition, males showed an increased blood lactate concentration ( P < .05), whereas females decreased the maximum velocity at zero load ( P < .01) and stroke rate ( P < .01). No change in the slope was observed for either sex ( P > .05). Conclusion : Following a 5-week off-season period, sprint swimming performance declines (males 0.34 s; females 1.15 s). The load–velocity profile and related variables evidenced deterioration, showing changes in blood lactate concentration, maximum load at zero velocity, average velocity during the third trial, and stroke rate.
This study examined the effects of caffeinated coffee (3 mg/kg) compared to decaffeinated coffee (placebo) on physical and cognitive performance in trained male athletes with morning (MT) and evening (ET) chronotypes, all of whom had moderate caffeine intake. Seventeen trained male athletes participated in various tests, including CP (a flanker task), hand grip strength test, back strength test, lower body Wingate sprint tests (peak and average power), and rating of perceived exertion (using the Borg Scale). The tests were conducted at two times of day: mornings (08:00 h−10:00 h) and evenings (16:00 h−18:00 h). Results indicated that caffeinated coffee significantly enhanced handgrip strength [F(1, 15) = 11.200, p = 0.001, η2p = .427], back strength [F(1, 15) = 8.695, p = 0.001, η2p = 0.367], and lower body Wingate test performance, including peak strength [F(1, 15) = 8.384, p = 0.001, η2p = 0.359] and mean strength [F(1, 15) = 8.304, p = 0.001, η2p = 0.356], regardless of chronotype. Conversely, no significant differences were observed in the cognitive performance (CP) measured by the flanker task and in Borg’s perceived exertion ratings. When analyzing the interaction between groups × CAF & PLA, significant differences were found in the handgrip strength test [F(3, 45) = 17.443, p = 0.001, η2p = 0.538], back strength test [F(3, 45) = 19.926, p = 0.001, η2p = 0.571], peak power [F(3, 45) = 12.285, p = 0.001, η2p = 0.450], and average power [F(3, 45) = 6.633, p = 0.009, η2p = 0.307]. However, no significant differences were noted in cognitive performance (CP) and Borg perceived exertion ratings. These findings suggest that chronotype, timing of training, and caffeine consumption can significantly influence physical performance in trained men with moderate caffeine intake.
The purpose of this study was to examine the effects of time of day on technical and physical performance parameters in young female tennis players. A sample of 12 recreational tennis players (age 24.2 ± 3.8 years) were randomly distributed into two groups. After having their demographics (age, experience, chronotypes), they were measured for body mass, body temperature, serve accuracy, serve speed, countermovement jump, grip strength, agility, and linear speed by counterbalancing method on two different days and at two different times of the day (09:00 and 16:30). The main results revealed that the players had significantly (p < 0.01) higher body temperature and greater values in the grip strength test during the afternoon session in comparison to the morning session. On the other hand, no significant differences (p > 0.05) were observed for other physical and technical performance parameters. The findings may highlight that time of day has no significant effects on several tennis-related performance determinants in female recreational players.
Circadian rhythms have been shown to be ubiquitous and critically important in the experimental laboratory, accounting for the difference between life and death in response to identical stimulus. The partly endogenous nature of circadian rhythms has been well documented and methods for their characterisation have been developed enabling the cellular and molecular mechanisms to be understood. Chronobiology and Chronomedicine aims to provide a review of these mechanisms underlying circadian rhythms and illustrate the role of the brain’s suprachiasmatic nuclei in the ‘pace-making’ process and the effects caused by ‘clock genes’ present in almost all cells. Beyond the mechanisms involved, the book discusses the relationship between body systems, disease, and proper circadian function; in particular, how disruption of the circadian rhythm is associated with ill health and disease status from observations made at the organismic level. The book is organised to be an ideal introduction for the postgraduate in various fields, reviewing developments and outlining methods to show the depth and breadth of chronobiology and chronomedicine, as well as an invaluable companion to researchers and healthcare professionals working in the field with an interest in developing novel therapeutic approaches.
Two experiments were conducted concerning diurnal variations in physical performance. Subjects were tested at 9 AM, 12 noon, and 3 PM on various physical parameters. Exp. 1 gave no significant differences among the three performances of grip strength and reaction times for 16 subjects. For seven subjects involved in Exp. 2, endurance ratios and torque accelerations, as recorded on a Cybex II, were used as criterion measures. A significant difference was found between the 9 AM and 3 PM performance of the flexion endurance ratio. No other differences were identified.
A morningness-eveningness questionnaire was administered to 34 golfers and 23 waterpolo-players to assess the influence of diurnal individual differences on the athletic performance levels. No differences in the diurnal type (“morning” vs “evening” individuals) were found among low-performing athletes, while in the high-performing group golfers had higher morningness scores than the waterpolo-players. The results suggest a relation between the diurnal type, performance level, and the time of day when the match is played (morning for golf and evening for waterpolo).
Two experiments are described that examined the influence of time of day of presentation on immediate and delayed retention, and the potential effects of time of day on retrieval from long-term memory. Time of presentation was found to influence both the immediate and delayed (28 day) retention of information presented in naturalistic contexts. However, while the trend in immediate memory over the normal waking day found in Expt 1 was exactly that predicted by a unidimensional arousal theory, the results of Expt 2 indicated that different circadian factors may be responsible for the time of presentation effects on immediate and delayed retention. Neither experiment yielded any evidence that time of day affects people's ability to retrieve information from long-term memory. The results are discussed within a circadian rhythm framework, and would appear to necessitate the adoption of a multifactor theory. It is suggested that further research is needed on (a) the effect of time of presentation on delayed retention, and (b) the nature of the changes in the encoding/storage processes responsible for such effects.
The responses of six healthy male subjects to submaximal and maximal exercise on a stationary bicycle ergometer have been investigated over a 24-hour period. Measurements were made on each subject at approximately three-hourly intervals and they included minute ventilation at a carbon dioxide output of 1-5 1 min-minus 1 (VE 1-5), tidal volume at a fixed VE of 30 1 min-minus 1 (VT 30), oxygen intake (VO2) at a work load (W) of 150 W (VO2 150), tympanic temperature (Tty) and cardiac frequency at a VO2 of 1-5 1 min-minus 1 (fH 1-5). The experiments were conducted in three parts: on the first occasion two subjects were measured during exercise; on the second occasion a further four subjects were observed in a similar way but starting from a baseline of zero load, and the measurements also included an estimate of cardiac output (Q) using a rebreathing technique. Finally the maximum aerobic power output (VO2max) was measured in three of the subjects in early morning and late evening. Diet and habitual physical activity were held constant between the exercise test on all three occasions. The results show that in the first two subjects fH 1-5 and Tty had a rhythmic pattern of variation with time of day whereas VE 1-5, VT30, and VO2 150 remained fairly constant. The variation in fH 1-5 was associated with Tty; the two variables reached a minimum at similar to 0500 hr and a maximum at similar 1200 hr. These results were confirmed on the remaining subjects but the changes in fH 1-5 and Tty were shown to be more variable and reduced in magnitude. Further, if the changes were calculated from a baseline of zero load, it was shown that the absolute changes observed in fH 1-5 and Tty were not due to the exercise per se but to changes in the basal level from which each subject operated. In addition it was shown that VO2 max and Q remained constant and were independent of the time of day. It is concluded that provided the exercise test conditions are rigidly standardized and subjects exercise from a controlled baseline there is no evidence for circadian variation in the change of responses to work at submaximal or maximal effort.
Blood glucose levels are commonly used as a marker of carbohydrate metabolism, and subsequent oscillations are related to various phenomena. Blood glucose levels are controlled by several hormones, i.e., insulin and the counterregulatory hormones. The circulating levels and the metabolic action of these hormones undergo different cyclic variations (Aparicio et al. 1974; Hautecouverture et al. 1975; Hoist et al. 1983; Lefebvre et al. 1987; Waldhausl 1989). These cyclic oscillations may influence the hormonal action on glucose consumption by peripheral tissues, glycogen degradation, and gluconeogenesis. The exogenous supply of glucose depends on food intake, produced by a food behavior which is regulated by pre- and periingestive factors which may stimulate or inhibit any motivation states such as hunger, satiety, satiation, or appetite (Nicolaïdis and Burlet 1988).
Rhythmicity characterizes many functions of the human organism, including those of the gastrointestinal (GI) system. Important and significant time-dependent changes have been documented in GI motility patterns [1, 2], drug intestinal absorption rates [3, 4], small bowel mucosal enzyme activities [5], mucosal DNA synthesis rates [6], and gastric acid secretion [7], among others [8]. The literature on chronobiologically oriented investigations in humans and animals, at both the organ and cellular level, is vast and beyond the scope of this discussion. This review will focus only on large amplitude rhythms of human GI motor, absorptive, and secretory function with real or potential influence on disease expression and/or treatment. Circadian rhythms will be emphasized although important ultradian rhythms of GI function will also be mentioned.
Asthma is a chronic obstructive airways disease. The underlying abnormalities are excessive contraction of tracheobronchial smooth muscle and hypersecretion of mucus plus musosal edema in association with airways inflammation (Spector 1982). Historical accounts of the disease describe a worsening of symptoms overnight. Nonetheless, most clinicians question the time dependency of this disease or feel that nocturnal asthma is a special subtype of asthma. In the majority of untreated patients asthma worsens, or occurs only, overnight. The increase in cough, wheeze, and breathlessness at this time causes substantial problems for patients (Pfeiffer et al. 1989). A number of hypotheses have been proposed to explain why asthma is so common overnight. These include day-night variations in certain environmental factors such as barometric pressure relative humidity, and ambient temperature; proximity and concentration of various offending antigens; accumulative effects of psychological and physiological stresses during the day; and assumption of a supine posture at night. An alternate explanation for the time dependency of this disease stresses the role of endogenous circadian bio-periodicities in relationship to changes in the external environment during each 24 h (Barnes 1984 a; Smolensky et al. 1981, 1986 a). With regard to chronobiological considerations, successful management of patients entails not only the institution of environmental control methods, but also an understanding of the circadian features of the disease to achieve a chronotherapy of anti-asthma medications (Reinberg et al. 1988a,b; Smolensky et al. 1986b, 1987a).
The inclusion of the pineal gland as a separate chapter, rather than a passing reference, in a book devoted to matters of clinical interest is witness to the enormous interest in the function of this organ in recent years. The investigation of the pineal gland in animals and humans has led not only to an understanding of its physiology but also to major advances in our understanding of biological rhythms and their importance in humans. Moreover, current research points to therapeutic approaches based on the fundamental science of pineal function, of importance particularly in psychiatry and occupational health.
With so much of the body and brain’s physiology and chemistry changing in a rhythmic circadian manner, it is hardly surprising to note that there are equivalent changes in a person’s mood, subjective activation and performance efficiency. Thus, an individual’s mental performance abilities are very different from one time of the day to another, and these changes over time can be categorized and studied using similar circadian techniques to those developed for the physiological measures (e.g., body temperature, blood pressure) more often studied by the chronobiologist. There are, however, several major differences that must be recognized if mental performance rhythms are to be studied properly. This chapter will start with a dicussion of these differences, then move on to discuss intertask differences in circadian mental performance rhythms, and the oscillatory changes underlying them.
If one examines living matter as a function of time under appropriate experimental conditions, on the cellular level, in tissue culture or in multicellular organisms, including man, at different levels of physiologic organization one invariably finds nonrandom variations of the variables examined (Aschoff and Wever 1976; Bünning 1973; Conroy and Mills 1970; Halberg 1959; Haus et al. 1980, 1988; Haus and Halberg 1980; Reinberg and Ghata 1964). Many of these time-dependent changes recur in regular intervals and thus represent rhythms, which are to a certain degree predictable in time. With the use of statistical procedures of rhythmometry, a large proportion of the variability encountered in most series of measurements of biologic variables can be shown to be due to a multitude of rhythms in different frequency ranges (Halberg et al. 1965 a, b; Halberg and Panofsky 1961; Halberg and Reinberg 1967; Haus et al. 1980, 1981; Panofsky and Halberg 1961), which may be superimposed upon each other and upon trends, e. g., as a function of aging. Chronobiology is the science investigating and objectively quantifying the mechanisms of this biologic time structure including the rhythmic manifestations of life (Halberg et al. 1977).
Twenty-six healthy, untrained men (23.3 +/- 4.4 years) were determined to be morning, intermediate or evening chronotypes using the 1976 Horne and Ostberg questionnaire. Each individual underwent a series of two maximal treadmill tests (Bruce protocol) at two different times of day: 7:30-8:30 a.m. (morning or M test), and 7:30-8:30 p.m (evening or E test). The M and E tests were administered a minimum of 48 hours apart using a randomized counter-balanced design. Heart rate, ventilation, oxygen consumption, carbon dioxide production, respiratory exchange ratio, rating of perceived exertion and total exercise time were monitored at each test session. Subject grouping, according to the questionnaire, revealed an age-related difference, with a higher mean age for the morning types compared to intermediate (t = 3.27, p < 0.01) or evening (t = 2.44, p < 0.05) types. Multivariate analysis of variance did not reveal significant differences in maximum exercise performance according to chronotype. Heart rate (F = 4.41, p < 0.05) and performance time (F = 5.13, p < 0.03) increased during the E test. While performance differences during maximum exercise were not detected between chronotypes, further study with submaximal exercise intensity and variable duration should be conducted.
The main aim of this study was to monitor changes in joint flexibility over 24 hours in 25 subjects. Measurements of finger tip to floor, lumbar flexion, lumbar extension, passive straight leg raising and glenohumeral lateral rotation at 90° abduction were taken every two hours during the 24 hour cycle. The presence of circadian rhythms in flexibility were established by graphical analysis of the results. These were shown to exist in all measurements, the most strong being finger tip to floor and most weak glenohumeral lateral rotation. The study also investigated grip strength over 24 hours and disclosed a circadian pattern in which there was a considerable fall in strength during the early hours and a rapid rise after 0600 hours.
Variations in plasma hormone concentrations have been studied extensively in various conditions of health and disease in the human and experimental animals. A wide range of environmental, metabolic, nutrient, and hormonal stimuli are known to modulate normal patterns of anterior pituitary hormone release and/or alter the metabolic clearance of the endocrine effector substance. The ability to evaluate quantitatively not only variations in plasma hormone concentrations but also regulated features of hormone secretory events has been acquired recently through the use of so-called deconvolution techniques [20, 26, 32, 36, 41, 48, 54, 56, 60, 62, 72, 71, 74]. Deconvolution represents a procedure in which available plasma hormone concentration measurements are interpreted mathematically as the specific consequence of definable secretory events and hormone-specific metabolic clearance. The examination of calculated in vivo secretory events is of particular importance pathophysiologically, when a clinician and investigator wish to assess regulation of the actual secretory behavior of the endocrine gland. In contrast, evaluation of plasma hormone concentrations in the conventional manner discloses information about the hormonal milieu to which the target gland is exposed. Although the majority of available clinical investigative work has focused on variations in plasma hormone concentrations (and hence, the signal made available to the target tissue), recent advances in analytical tools have allowed detailed studies of the secretory rhythms inherent in the regulated output of the endocrine gland. Accordingly, here we will emphasize not rhythms in pituitary hormone concentrations in plasma, but rhythms in the secretory behavior of the anterior pituitary gland under a range of normal and pathological conditions in man.
86 guidelines for shiftworkers were assembled by a team of European experts and published as the Bulletin of Shiftwork Topics No. 3. Before publication, 24 of the personally directed guidelines were tested against the normal actions of two groups of mixed sex industrial 3-shift continuous workers (n = 120). Six of the guidelines were endorsed as their practice by a majority of both groups; six were opposed by a majority of both groups; and twelve were intermediate. The six that were opposed are closely examined. Half of them fall into specific remedies for sleep problems, that were more abruptly phrased in the questionnaire than in the guidelines. The other three are concerned with eating and drinking: breaking your sleep to join in a family meal is only a gentle suggestion in the guidelines, and not a sensible general recommendation for day-sleepers; avoiding fatty foods may only be appropriate if you have digestive problems; and avoiding coffee and tea in the last two hours before sleep appears to oppose and lose out to work and home pressures. An evaluated intervention is required to check these points.
The author presents a discussion of the steady states (homeostases) of the body, with the explanation, so far as such is possible, of the mechanisms controlling such conditions. The account is closed with analogies between the regulation of the body and the regulation of social processes. Brief bibliography. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Brain slices, containing the suprachiasmatic nuclei, of rats were removed at various times of the fay and the firing rates of single cells were recorded. The firing rates were found to maintain a circadian rhythm in temporal accord with the light/dark cycle of the donor animal, and were highest during the lights on phase.
A brief review of the literature, and three experiments, are presented which investigated time of day effects in human performance at simple repetitive tasks (i.e. tasks involving little or no ‘working memory’ load) The goal was to differentiate between a ‘capacity’ based explanation of the effects, concerned with changes in the general rate of information processing, and a ‘strategy’ based one concerned with the amount of information processed at each decision point. The strategy based explanation appeared to be the more suitable, accounting for the surprising heterogeneity in time of day function that was found for such tasks in the literature, and for the results of the three experiments. It would appear that there might be a general tendency for people to become faster but less accurate as the day wears on.
Aerobic running exercise in six Ss changed endogenous core body temperature and melatonin rhythm phases by 2-3 hours between early morning running and early evening running conditions.
This study reports no significant change in the pattern of the utility of leisure time in response to a change from a slowly rotating to a more quickly rotating shift system by shiftworkers in the German chemical industry. An experimental and a control group were surveyed. The experimental group of 80 shiftworkers completed time utility ratings before and after a change from a weekly continuous 4–shift system to a quickly rotating continuous 5–shift system. A control group of 23 shiftworkers remained on the weekly rotating system and completed time utility ratings at the same time points as the experimental group. Exploratory analysis of the experimental group's (n= 112) leisure time utility ratings prior to the shift system change is presented for subgroups (determined by age, marital status and the presence or absence of children in the home) and for the subgroup of 22 shiftworkers who indicated dissatisfaction with the weekly rotating shift system and strong satisfaction with the more quickly rotating system. The analysis suggests that leisure time utility may be a useful parameter for use in future studies of satisfaction with shiftwork systems.
Thesis (M.A.)--California State University, Northridge, 1990. Includes bibliographical references.
Heart rate (HR) and rectal temperature (RT) data were obtained from 12 female and 27 male subjects. The subjects were housed in a facility where the environment was controlled. Human male and female RT and HR exhibit a circadian rhythm with an excursion of about 1.2 C and 30 beats/min, respectively. The acrophases, amplitudes, and level crossings are only slightly different between the sexes. The male HR and RT circadian wave forms are more stable than those of the females. However, the actual RT and HR of males were always lower than that of females at all time points around the clock. The HR during sleep in females is 15 per cent below the daily mean heart rate and in males, 22 per cent.
In two groups of healthy children synchronized with a diurnal activity (light-on at 07.00) and a nocturnal rest(light-off at 21.00), lug resistance (R1) and dynamic lung compliance (C1 dyn) were measured at fixed clock hours (07.30, 11.30, 16.30, 22.30). The measurements were performed before and 10 minutes after the inhalation of bronchodilators (a beta-sympathetic stimulating agent (orciprenaline, dose 2 mg) and a vagolytic agent (SCH 1000, doses 80 mug and 200 mug). A circadian rhythm is detected for R1 and C1 dyn and quantified by the cosinor method. R1 and C1 dyn acrophase (peak time in the 24-h scale) are not significantly different for both groups: they are located for R1 at 05.39 and 03.31, for C1 dyn at 09.31 and 12.51. R1 and C1 dyn circadian rhythms are not detectable both after 2 mg orciprenaline and 200 mug SCH 1000 inhalation. This chronopharmacologic effect of the bronchodilators might be considered indirect evidence of a circadian rhythm in the bronchial tone. This latter may be related to circadian changes in neurovegetative activity. A dose-effect difference of the vagolytic agent on R1 at night seems to indicate a relative nocturnal prominence of the vagal tone.
Six studies on sleep/wake patterns and circadian rhythms were carried out. In summary: (1) Adrenaline excretion, self-rated activation, and body temperature rhythms persisted during sleep deprivation, resisted adjustment to rotating shift work, but adjusted rather well to permanent night work. Noradrenaline adjusted to most schedules and lost its rhythm during sleep deprivation. When night sleep was reintroduced the noradrenaline rhythm reappeared while the existing adrenaline rhythm was accentuated. (2) Exposure to a performance stressor at the trough raised adrenaline to daytime levels. An equally large response was seen at the peak. (3) Interindividual day-to-day consistency of 3 and 24 hour levels was high for both catecholamines. Intraindividual consistency of the 24-hour pattern was high for adrenaline but low for noradrenaline. Cosine estimates of adrenaline phase showed a considerable intraindividual consistency while interindividual consistency was poor. Noradrenaline had poor cosine fit. (4) Sleep deprivation did not change catecholamine excretion either during the vigil or during recovery sleep. (5) It was concluded that adrenaline excretion, rated alertness, and body temperature exhibited self-sustained circadian rhythms which made adjustment to new sleep/wake patterns very difficult, and that the noradrenaline excretion rhythm depended on exogenous factors.
While living under constant conditions and complete isolation from environmental time cues for about 4 weeks, 9 male subjects exercised on a bicycle ergometer seven times per 'day' during two weeks and refrained from physical activities during the other 2 weeks. The freerunning circadian rhythms of wakefulness and sleep and of rectal temperature showed, on the average, no difference between the two sections with regard to the autonomous period and the tendency towards internal desynchronization. Even in the one experiment in which the two rhythms became internally desynchronized, the periods of the rhythms remained unchanged during the time the subject worked on the bicycle. Only in one out of the nine subjects, the autonomous period was considerably longer under the influence of work than without it. The hypothesis is advanced that the period of an autonomous rhythm becomes normally independent of physical workload by way of a compensation mechanism.
Circadian rhythmicity in resting, exercise and recovery pulse rates was studied using five male subjects. Resting pulse rate data were collected at seven seperate times during a 24 hour period. Exercise and recovery pulse rate data were collected at the exact same limes, as follows: 0400, 0800, 1200, 1500, 1800, 2100 and 2400 h. The lowest resting pulse rates for all subjects occurred between 0400 and 0800 h; highest resting pulse rates occurred between 1800 and 2400 h. Exercise pulse rates followed this same general pattern, and tended to amplify the circitdiun rhythmicity.
Subjects who slept for 4 h from 0000, and for a second 4 h variously distributed over the day, have provided values for rectal temperature and for urinary excretion of water, potassium, sodium, chloride, phosphate, creatinine, calcium and urate in the sleeping subject at all hours of the 24. These are compared with similar values in the wakeful subject. Temperature was lower during sleep at all hours except 1000 and 1200, and the difference was maximal shortly before 0000. At all hours potassium excretion was lower and phosphate excretion higher during sleep. Cosinor analysis of the different variables in the sleeping subject is compared with that in subjects following nycthemeral habits, and the interaction between endogenous rhythms and external influences such as sleep is discussed. The phasing of the temperature and urinary rhythms was essentially normal by the end of the observations. By contrast in a subject who slept at irregular hours mimicking the habits of an air pilot a free-running rhythm unrelated to the habits of sleep emerged. When he was finally living again on normal time his temperature and urinary acrophases had moved to the middle of the night. Phosphate excretion was largely exogenous, falling consistently when subjects rose after 8 h, but not after 4 h of sleep.
The volume, pH and composition of 24-h urine samples, collected by 13 healthy male adults, were followed over a period of one year. Significant and systematic variations in urine pH, calcium, phosphate, oxalate, uric acid, potassium and magnesium were observed. A significant but non-sinusoidal variation in sodium excretion was found but there were no significant changes in urinary volume, creatinine or hydroxyproline. Many of the observed changes could be attributed to variations in the pattern of food consumption throughout the year but calcium, phosphate and oxalate were exceptions in that seasonal variations in these parameters appeared to be due to the effects of sunlight (or vitamin D) rather than to the diet.
Research into individual differences in circadian rhythms is reviewed, particularly morningness-eveningness. It was hypothesised that extraverts would be inclined towards eveningness and introverts towards morningness. Forty-eight subjects took regularly their oral temperature. Peak times were identified from smoothed temperature curves. Results showed that extraverts had a peak time insignificantly later than introverts. Re-grouping of the data into the morningness-eveningness dimension, based upon the results of a self assessment questionnaire, showed that evening types had significantly later peak times than morning types. Morningness-eveningness was not significantly ocrrelated with extraversion-introversion, although there was a trend. No significant differences were found for sleep lengths with either groupings, or for sleep-wake habits within extraversion-introversion. Morning types retired and arose significantly earlier than evening types. Although sleep-wake habits and extraversion-introversion help to determine peak times there are other contributory factors to peak time which appear to be partly covered by the questionnaire.
Interindividual differences in circadian rhythms of urinary catecholamine excretion, performance, self-ratings of arousal and oral temperature were studied in 80 subjects divided into three groups--morning-active, evening-active, and intermediate. Catecholamine excretion, body temperature, and self-ratings of arousal exhibited pronounced circadian variations. Morning-active subjects exceeded other groups in the 24 h level of adrenaline excretion but crest phases did not differ, occurring close to 13.00 h. No differences between groups were found for noradrenaline excretion. Crest phases occurred close to noon. Self-rated alertness exhibited a significantly earlier (14.12 h) crest phase for morning-active than for evening-active subjects (16.09 h). The performance did not differ between groups.
The physical working capacity (PWC) of 303 male adolescents was measured using the PWC170 test. The changes in PWC with age were similar to those reported by other workers; the PWC of male adolescents in Ireland
appears to be similar to that of North American subjects and may be somewhat lower than that of subjects in some other parts
of the world. There was no evidence to suggest a relationship between PWC and level of habitual activity in the younger subjects
but heavy physical activity was found to be related PWC in post adolescents.
In this paper, evidence for circadian and other rhythms in cardiac and circulatory function is reviewed through the evaluation of earlier published data by least squares spectral and cosinor analyses. While the focus, herein, is on the documentation of temporal (mainly 24 h) changes in cardiovascular function of healthy human subjects using previously reported data, additional recent findings of ours from studies on patients as well as on human primates are included when relevant. Even though the aim of this paper is to present a comprehensive picture of circadian changes in cardiac and circulatory functions, it must be pointed out that data for this review were obtained from authors who studied individuals of various ages and levels of cardiovascular fitness and health. For example, studies cited pertain to investigations carried out on infants as well as elderly subjects, although most were carried out on healthy adults. Therefore, due to the wide range in age of subjects, and because of expected changes in cardiovascular function which occur with advancing chronologic age, even in healthy samples, simple and all inclusive statements about temporal characteristics, i.e. mesor, amplitude and acrophase for a given rhythm, can not be formulated indiscriminately for application to all individuals. Nonetheless, results of chronobiologic analyses on data obtained from several samples of healthy subjects, such as the variables of heart rate as well as systolic, diastolic and pulse pressure, reveal remarkable agreement for the aforementioned rhythmometric endpoints. Furthermore, several important aspects of cardiovascular function are yet to be studied for temporal variability. Because of this, several gaps exist, and a complete presentation of the temporal organization of the cardiovascular system is not possible at this time. However, this review does attempt to bring together relevant findings in order to present what is now known so that prospective investigations can be undertaken to verify previously reported findings, and more importantly, to provide new data on temporal aspects of cardiac and circulatory function not as yet studied. New investigations are needed to provide greater insight into the suspected existence of circadian susceptibilities to arrhythmias, coronary occlusion and stroke. If indeed such circadian or other susceptibility rhythms are documented, for example, as was the case for the nocturnal occurrence of asthma, the chronopharmacologic implications are obvious. The findings here reported documenting circadian rhythms in cardiovascular function, and those found by others on cardiac morbidity and mortality or on the manifestation of arrhythmias in recent myocardial infarct patients, suggest that treatment of heart disease be considered according to a possible circadian requirement for medications. The suspicion of circadian rhythms in cardiac dysfunction indicates the need for chronopharmacologic investigations of cardiac medications. Although some chronopharmacologic work has been initiated with respect to disorders other than cardiovascular ones, prospective studies must include aspects of the bioavailability of medication as well as the timing of treatments to achieve the best therapeutic advantage in patients with cardiac dysfunction. Chronopharmacologic methods with respect to synthetic corticosteroids have already proven useful in managing several steroid dependent illnesses. It is anticipated that chronopharmacologic investigations applied to cardiovascular disease will result in a re evaluation of dosage and administration schedules of medications with regard to circadian and possibly other period rhythms. (142 references are cited).
The circadian effects of an aerobic training program were studied in 3 groups of men who exercised at different times of day. Twelve healthy sedentary men were assigned to morning (9:00-9:30), afternoon (15:00-15:30) or evening (20:00-20:30) exercise groups. Each group performed a 30-minute 60% VO2max cycle ergometer exercise 4 days per week over a 4-week period. Maximal oxygen uptake (VO2max) was estimated and adaptive responses of heart rate and blood lactate levels to the training program were measured. After 4 weeks, the afternoon group showed a significant increase in estimated VO2max. A significant decrease in heart rate and blood lactate responses occurred in the afternoon and morning groups and the afternoon and evening groups, respectively. These results suggest that aerobic training is most effective in the afternoon.
Previous work has demonstrated that exercise performance varies with time of day. The aim of this study was to investigate the influence of time of day on measures of anaerobic power and anaerobic capacity. Twelve male subjects, aged 18-22 years, performed a stair run test, a standing broad jump and the Wingate Anaerobic Test on twelve separate occasions. These were at 02:00, 06:00, 10:00, 14:00, 18:00 and 22:00 hours, duplicate measurements being obtained at each time point. Subjects' diet and activity prior to exercise and the laboratory temperature were controlled. Pre-exercise rectal temperature was measured on each occasion. The rectal temperature data conformed to a cosine function: its peak occurred at 18:11 hours and the peak to trough variation was 0.76 degrees C (p < 0.001). There was a rhythm in performance on the stair run and the broad jump tests, in phase with the curve in rectal temperature. Results for peak power and mean power production on the Wingate test did not display a significant circadian rhythm. The stair run and broad jump tests seem to be more sensitive to circadian rhythmicity than does the Wingate Anaerobic Test.
This study evaluated the effect of time of day on performance of high-intensity, constant-power cycle ergometry by both men and women. Subjects performed all-out cycle ergometer tests in the morning and in the afternoon in randomized order. For all tests, work rate was a constant 5.0 W.kg-1 (women, n = 6) or 6.0 W.kg-1 (men, n = 8). Total work performed was 9.6% greater in the afternoon (mean +/- SE, 348.8 +/- 40.6 J.kg-1) compared to the morning (318.2 +/- 39.5 J.kg-1). The greater amount of work in the afternoon was associated with a 5.1% higher aerobic power and a 5.6% larger anaerobic contribution. There was no interaction between gender and the effect of time of day on the aerobic or anaerobic contributions. These results provide evidence of a circadian rhythm in aerobic and anaerobic responses to high-intensity short-duration exercise, in women as well as in men.