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Effect of Time of Day and Partial Sleep Deprivation on Short-Term, High-Power Output
Chronobiology International
Abstract and Figures
The purpose of this study was to determine whether delaying bedtime or advancing rising time by 4 h affects anaerobic performance of individuals the following day in the morning and afternoon. Eleven subjects participated in the study, during which we measured the maximal, peak, and mean powers (i.e., P(max) [force-velocity test], P(peak), and P(mean) [Wingate test], respectively). Measurements were performed twice daily, at 07:00 and 18:00 h, following a reference normal sleep night (RN), a partial sleep deprivation timed at the beginning of the night (SDB), and a partial sleep deprivation timed at the end of the night (SDE), and oral temperature was measured every 4 h. Each of the three experimental conditions was separated by a one-week period. Our results showed a circadian rhythm in oral temperature, and analysis of variance revealed a significant sleep x test-time effect on peak power (P(peak)), mean power (P(mean)), and maximal power (P(max)). These variables improved significantly from the morning to the afternoon for all three experimental conditions. Whereas the morning-afternoon improvement in the measures was similar after the RN and SDB conditions, it was smaller following the SDE condition. There was no significant difference in the effect of the two sleep-deprivation conditions on anaerobic performances at 07:00 and at 18:00 h under the SDB condition in comparison with the post-reference night. However, the performance variables were significantly lower at 18:00 h after the SDE condition. In conclusion, a 4 h partial sleep deprivation at the end of the night appears to be more disturbing than partial sleep deprivation at the beginning of the night.
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... Além disso, há a compreensão de que, dos componentes passíveis de comprometimento em decorrência da PS/PPS, o cérebro é aquele que agrega os maiores riscos (HOBSON, 2005). Dos parâmetros anaeróbios avaliados, o pico de potência é o desfecho mais testado (ABEDELMALEK et al., 2013;HAJSALEM et al., 2013;MOUGIN et al., 1996;SOUISSI et al., 2003SOUISSI et al., , 2008SYMONS;MYLES, 1988;TAHERI;ARABAMERI, 2012), seguido da potência máxima e do perfil força x velocidade (SOUISSI et al., 2003(SOUISSI et al., , 2008. ...
... Além disso, há a compreensão de que, dos componentes passíveis de comprometimento em decorrência da PS/PPS, o cérebro é aquele que agrega os maiores riscos (HOBSON, 2005). Dos parâmetros anaeróbios avaliados, o pico de potência é o desfecho mais testado (ABEDELMALEK et al., 2013;HAJSALEM et al., 2013;MOUGIN et al., 1996;SOUISSI et al., 2003SOUISSI et al., , 2008SYMONS;MYLES, 1988;TAHERI;ARABAMERI, 2012), seguido da potência máxima e do perfil força x velocidade (SOUISSI et al., 2003(SOUISSI et al., , 2008. ...
... Nenhum estudo para este parâmetro foi realizado com atletas de voleibol ou voleibol de praia, que seja do nosso conhecimento, e cinco avaliaram a PPS (ABEDELMALEK et al., 2013;HAJSALEM et al., 2013;MOUGIN et al., 1996;SOUISSI et al., 2003SOUISSI et al., , 2008. Baseado nos resultados destes estudos, é essencial adotar cautela para eventuais conclusões dado, Ainda, a PS/PPS foi induzida para a análise de diversos desfechos para força muscular em populações heterogêneas (BULBULIAN, 1996;HAJSALEM et al., 2013;MENEY et al., 1998;REILLY;DEYKIN, 1983;REILLY;PIERCY, 1994;SKEIN et al., 2011;SOUISSI et al., 2013;SYMONS;MYLES, 1988;TAKEUCHI et al., 1985). ...
A fadiga mental (FM) e a privação/privação parcial do sono (PS/PPS), por si só, prejudicam o desempenho percepto-cognitivo e físico de atletas das mais variadas modalidades esportivas. Estudos que avaliem os efeitos da FM e PPS conjugados, que individualizem a carga cognitiva e a duração da PPS e que analisem o desempenho percepto-cognitivo e físico de atletas de voleibol de praia a partir de testes ecológicos são necessários. Esse estudo teve como objetivo analisar os efeitos da PPS e da FM, conjugadas e isoladas, no desempenho percepto-cognitivo e físico em atletas treinados de voleibol de praia. Participaram do estudo 14 atletas treinados de voleibol de praia (12 homens; 17,6±1,5 anos). O estudo foi do tipo experimental de medidas repetidas, cruzado e randomizado e adotou quatro condições experimentais: a) Controle (CT), b) FM, c) PPS e d) PPS+FM. A FM foi induzida pelo Stroop task incongruente e a atividade de sono dos voluntários foi monitorada por oito noites consecutivas. A carga cognitiva e a duração da PPS foram individualizadas. O cumprimento da PPS foi monitorado por formulário online, preenchido em intervalos de 15 minutos pelo tempo que perdurou a PPS. O desempenho físico foi medido por uma série de 50 saltos com contramovimento com intervalos de 5 segundos entre cada salto realizados em esforço máximo e o desempenho percepto-cognitivo foi avaliado via testes visuomotores com luzes de light emitting diode (LED) que simularam ações de defesa e bloqueio no voleibol de praia. Os desfechos primários do estudo foram analisados pela análise de variância ANOVA de um fator (condição [4]) e o post-hoc de bonferroni foi aplicado para localizar as eventuais diferenças estatisticamente significantes. Os dados contínuos estão apresentados como média e desvio padrão e os categóricos como valores absolutos e relativos. A condição PPS causou respostas mais lentas no tempo de reação (TR) “mais rápido” (p=0,02; d de Cohen=1,12; PPS: 1562.14±109.06 ms vs CT: 1440.71±101.41 ms) e “média” (p=0,02; d de Cohen=1,13; PPS: 1874.29±144.63 ms vs CT: 1727.14±113.30 ms) do teste visuomotor de defesa comparado ao CT e a condição PPS+FM apresentou prejuízo no TR “média” (p<0,01; d de Cohen=1,38; PPS+FM: 1906.43±133.45 ms vs CT: 1727.14±113.30 ms) do mesmo teste comparado ao CT. Para o teste visuomotor de bloqueio foi observado que a condição PPS+FM prejudicou o TR “média” (p=0,04; d de Cohen=1,06; PPS+FM: 722.14±100.09 ms vs CT: 631.42±82.17 ms) e “índice de desempenho” (p=0,02; d de Cohen=1,18; PPS+FM: 0,14±0,02 u.a vs CT: 0,16±0,02 u.a) comparado ao CT. O desempenho físico não foi prejudicado por nenhuma condição experimental. Conclui-se, portanto, que a PPS, isolada e conjugada à FM, prejudicam o desempenho percepto-cognitivo de atletas treinados de voleibol de praia, entretanto, os prejuízos da PPS conjugados à FM não se sobrepõem àqueles observados na PPS quando isolada. Adicionalmente, o desempenho físico não foi prejudicado nem pela FM nem pela PPS em atletas treinados de voleibol de praia.
... It is crucial to explore the immediate and prolonged impacts of both positive and negative aspects of caffeine consumption on physical and mental well-being (including better academic performance). Notably, caffeine exhibits a recognized stimulant effect, as evidenced by studies such as Barry et al. (Barry et al., 2008), contributing to heightened alertness and faster reaction times upon consumption (Souissi et al., 2008). The peak concentration of caffeine in the body occurs approximately 45 to 60 minutes after ingestion, as indicated by Krieger et al. (Krieger et al., 2016). ...
... known to increase focus and cognitive abilities. Several research paper found that the moderate intake of caffeine containing beverage can foster awareness, boost reaction ability, and improve physiological mood, participating to an overall improvement in cognitive enhancement (Barry et al., 2008;Souissi et al., 2008), which can cause to better academic results (Santos et al., 2010). Likewise, the enhanced focus and improved physiological mood may positively impact a student's overall attention and participation in academic activities. ...
... The negative impact of sleep loss on endurance performance may be influenced psychologically, such as motivation [199]. Lack of sleep seems to negatively impact evening performance more than morning performance [199][200][201]. After sleep loss, decreasing CR amplitude probably causes decreased performance in the evening [200,202]. ...
... Only a few studies measure performance after total sleep deprivation [199,200], a restriction that would have produced less meaningful outcomes. Regarding relative sleep deprivation, missing the first few hours of the night doesn't seem to affect performance [201,203,204]. However, partial sleep deprivation over multiple days has been shown to have the opposite effect, probably because it increases perceived effort, sleepiness, and weariness [205]. ...
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.
... Athletes performing at the elite and collegiate levels have been reported to lack the necessary sleep for optimal performance (Bolin, 2019;Lastella et al., 2015). Impaired or restricted sleep can lead to reduced mean power production in male footballers Abedelmalek et al. (2013) and male physical education students (Souissi et al., 2008). Furthermore, evidence suggests that lack of sleep also affects lower body strength (Reilly & Piercy, 1994) and cardiovascular performance (Azboy & Kaygisiz, 2009). ...
As the demands of training and competition increase so does the potential risk of injury and illness to the athlete whilst seeking to maximize their adaptive processes to promote optimal performance. Therefore, as a strategy to mitigate this risk, strength and conditioning coaches need reliable and valid monitoring tools to track an athlete's status throughout training to ensure the progression of adaptation, and that the athlete remains healthy throughout the adaptation process. The purpose of this article is to provide the reader with an evidence-driven outline of basic, simple, and cost-effective monitoring tools that are reliable and valid to observe the fitness/fatigue paradigm and track overall athlete physical adaptation and health throughout the training process, suitable for most settings. A weekly example calculating sessional ratings of perceived exertion (sRPE), training load, monotony, and strain is provided along with a basic monitoring system as a guide for the reader.
... Athletes are more susceptible to poor sleep quality and duration due to several constraints (such as training/competition demands; time-zone transition disturbing circadian rhythms; psychological issues or environmental factors), achieving an average of 6.5-6.7 h per night (Craven et al. 2022;Sargent et al. 2014;Simpson et al. 2017;Walsh et al. 2021). Due to the fundamental importance of the sleep-wake cycle, circadian rhythm disturbances can be detrimental on physiological and psychological measures, and likely hinder cognitive and some components of sporting performance, with greater deterioration the more sleep loss is accumulated Souissi et al. 2008). ...
We have investigated the effects that partial-sleep-restriction (PSR0, 4-h sleep retiring at 02:30 and waking at 06:30 h for two consecutive nights) have on 07:30 and 17:00 h cognitive and submaximal weightlifting; and whether this performance improves at 17:00 h following a 13:00 h powernap (0, 30 or 60-min). Fifteen resistance-trained males participated in this study. Prior to the experimental protocol, one repetition max (1RM) bench press and back squat, normative habitual sleep and food intake were recorded. Participants were familiarised with the testing protocol, then completed three experimental conditions: (i) PSR with no nap (PSR0); (ii) PSR with a 30-min nap (PSR30) and (iii) PSR with a 60-min nap (PSR60). Conditions were separated by 7 days with trial order counterbalanced. Intra-aural temperature, Profile of Mood Scores, word-colour interference, alertness and tiredness values were measured at 07:30, 11:00, 14:00, 17:00 h on the day of exercise protocol. Following final temperature measurements at 07:30 h and 17:00 h, participants completed a 5-min active warm-up before performing three repetitions of left and right-hand grip strength, followed by three repetitions at each incremental load (40, 60 and 80% of 1RM) for bench press and back squat, with a 5-min recovery between each repetition. A linear encoder was attached perpendicular to the bar used for the exercises. Average power (AP), average velocity (AV), peak velocity (PV), displacement (D) and time-to-peak velocity (tPV) were measured (MuscleLab software) during the concentric phase of the movements. Data were analysed using general linear models with repeated measures. The main findings were that implementing a nap at 13:00 h had no effect on measures of strength (grip, bench press or back squat). There was a main effect for time of day with greatest performance at 17:00 h for measures of strength. In addition to a significant effect for "load" on the bar for bench press and back squat where AP, AV, PV, D values were greatest at 40% (P < 0.05) and decreased with increased load, whereas tPV and RPE values increased with load; despite this no interaction of "load and condition" were present. A post lunch nap of 30- and 60-minute durations improved mood state, with feelings of alertness, vigour and happiness highest at 17:00 h, in contrast to confusion, tiredness and fatigue (P < 0.05), which were greater in the morning (07:30 h). The word-colour interference test, used as an indicator of cognitive function, reported significant main effect for condition, with the highest total test score in PSR60 condition (P = 0.015). In summary, unlike strength measures the implementation of a 30 or 60-minute nap improved cognitive function when in a partially sleep restricted state, compared to no nap.
... et al., 2008;Van Helder & Radomski, 1989). The majority of the previous literature surrounding this topic has focused on a full night of sleep deprivation preceding the anaerobic exercise performance the following day. ...
The study aim was to determine the effect of sleep restriction (3 h) between consecutive days of exercise on sprint and endurance cycling performance, wellness, and mood. A total of 10 well-trained males performed 2 consecutive-day trials separated by a normal night sleep (control [CONT]; mean [SD] sleep duration 3.0 [0.2] h) or sleep restriction (RES; mean [SD] sleep duration 3.0 [0.2] h). Experimental trials included a 90-min fixed-paced cycling bout and the respective sleep conditions on Day 1, followed by two 6-s peak power (6-s PP) tests, a 4- and 20-min time trial (TT) on Day 2. Profile of Mood States (POMS) and wellness questionnaires were recorded on Day 1 and Day 2. Blood lactate and glucose, heart rate (HR), and rating of perceived exertion were recorded throughout Day 2. Power output (PO) was significantly reduced for RES in the 6-s PP trial (mean [SD] 1159 [127] W for RES versus 1250 [186] W for CONT; p = 0.04) and mean PO during the 20-min TT (mean [SD] 237 [59] W for RES versus 255 [58] W for CONT; p = 0.03). There were no differences for HR, lactate and glucose, or POMS between CONT and RES in all experimental trials (p = 0.05-0.89). Participants reported a reduction in overall wellness prior to exercise on Day 2 following RES (mean [SD] 14.5 [1.6] au) compared to CONT (mean [SD] 16 [3.0] au; p = 0.034). Sleep restriction and the associated reductions in wellness, reduce cycling performance during consecutive days of exercise in a range of cycling tests that are relevant to both track and road cyclists.
... Consequently, sleep deprivation's deleterious effect should be more extensive in the studies that assessed endurance performance after midday. Indeed, sleep deprivation has been found to worsen afternoon, but not morning, anaerobic performance (Souissi et al., 2003;Souissi et al., 2008). However, in our study, the exercise testing time of day did not influence the sleep deprivation's deleterious effect on endurance performance. ...
We conducted a systematic review and meta-analysis to investigate the effect of sleep deprivation on endurance performance, as well as possible effect-modifying factors. Searches were done in Pubmed, Web of Science, Embase, and Scopus on 12 July 2022. We additionally searched the bibliographic references and citations on Google Scholar of the papers whose full text was analyzed. Eligible studies were randomized and non-randomized controlled trials that compared sleep deprivation and habitual-sleep night effects on endurance performance in healthy humans. The studies’ quality was examined by the Cochrane Collaboration’s risk of bias tool. We calculated the pooled standardized mean differences (pooled SMD) and 95% confidence interval (95%CI) by a random-effects model. A mixed-effects model analyzed subgroups. Thirty-one studies were analyzed (n = 478), generating 38 effect sizes in full. The overall risk of bias was low in 8% of the studies, unclear in 74%, and high in 18%. Sleep deprivation in general had a moderate negative effect on endurance performance (polled SMD [95%CI] = -0.52 [-0.67; -0.38]). Training status, sleep deprivation magnitude, assessment time, exercise mode, and endpoint type did not influence the sleep deprivation effect, whereas longer exercises (>30 min) were more affected by sleep deprivation than shorter ones (P = 0.035). Therefore, the available evidence supports that sleep deprivation's deleterious effect on endurance performance is of moderate size and depends on exercise duration. This information can be useful to estimate the performance decrement of endurance exercise practitioners under sleep deprivation in training routines and competitions.
PROSPERO registration number CRD42021229717.
This chapter aims to illustrate the impact of sleep deprivation on athletic performance. Sleep research distinguishes between total, partial, and selective sleep deprivation. In rats, sleep deprivation of two to three weeks leads to death under experimental conditions. In humans, due to ethical reasons, only shorter periods of sleep deprivation have been studied. Here too, losses are primarily seen in cognitive performance, with microsleep episodes in particular reducing performance after sleep deprivation. In addition, there are negative changes in memory formation, pain perception, the immune system, and metabolism. The effects on motor skills such as strength and endurance are rather minor due to sleep deprivation. Various recommendations for action arise for sports practice, although various questions still need to be investigated.
An English language self-assessment Morningness-Eveningness questionnaire is presented and evaluated against individual differences in the circadian vatiation of oral temperature. 48 subjects falling into Morning, Evening and Intermediate type categories regularly took their temperature. Circadian peak time were identified from the smoothed temperature curves of each subject. Results showed that Morning types and a significantly earlier peak time than Evening types and tended to have a higher daytime temperature and lower post peak temperature. The Intermediate type had temperatures between those of the other groups. Although no significant differences in sleep lengths were found between the three types, Morning types retired and arose significantly earlier than Evening types. Whilst these time significatly correlated with peak time, the questionnaire showed a higher peak time correlation. Although sleep habits are an important déterminant of peak time there are other contibutory factors, and these appear to be partly covered by the questionnaire. Although the questionnaire appears to be valid, further evaluation using a wider subject population is required.
An investigation along the circadian time scale in heart rate (HR), rectal temperature (Tr) and metabolic functions at rest, during submaximal and maximal exercise, and post-exercise was conducted using 15 male subjects. Each individual performed a cycle ergometer test on six separate days, temporally placed over the solar day to incorporate equidistant observation points. The exercise tests involved two consecutive 5-min loads at 82 and 147 W, then a graded increase of work-rate every 2 min to exhaustion. Significant circadian rhythms were evident at rest for HR, Tr, VO2 and VE, the HR acrophase at 13:50 hr leading that of the Tr and metabolic variables significantly (P less than or equal to 0.05). The circadian rhythms in metabolic measures were not evident at any exercise level or post-exercise and muscular efficiency was found to be independent of time of day. The exercise tolerance time and blood lactate post-exercise values failed to show a significant rhythm. In contrast the rhythms in HR and Tr were retained with similar phase and amplitude to those at rest during all work rates and post-exercise, though the amplitude of the HR cycle was attenuated at maximum.
Anaerobic tests are divided into tests measuring anaerobic power and anaerobic capacity. Anaerobic power tests include force-velocity tests, vertical jump tests, staircase tests, and cycle ergometer tests. The values of maximal anaerobic power obtained with these different protocols are different but generally well correlated. Differences between tests include factors such as whether average power or instantaneous power is measured, active muscle mass is the same in all the protocols, the legs act simultaneously or successively, maximal power is measured at the very beginning of exercise or after several seconds, inertia of the devices and body segments are taken into account.
Force-velocity tests have the advantage of enabling the estimation of the force and velocity components of power, which is not possible with tests such as a staircase test, a vertical jump, the Wingate test and other long-duration cycle ergometer protocols. Maximal anaerobic capcity tests are subdivided into maximal oxygen debt test, ergometric tests (all-out tests and constant load tests), measurement of oxygen deficit during a constant load test and measurement of peak blood lactate. The measurement of the maximal oxygen debt is not valid and reliable enough to be used as an anaerobic capacity test. The aerobic metabolism involvement during anaerobic capacity tests, and the ignorance of the mechanical efficiency, limit the validity of the ergometric tests which are only based on the measurement of work. The amount of work performed during the Wingate test depends probably on glycolytic and aerobic power as well as anaerobic capacity. The fatigue index (power decrease) of the all-out tests is not reliable and depends probably on aerobic power as well as the fast-twich fibre percentage. Reliability of the constant load tests has seldom been studied and has been found to be rather low. In theory, the measure of the oxygen deficit during a constant load test is more valid than the other tests but its reliability is unknown. The validity and reliability of postexercise blood lactate as a test of maximal anaerobic capacity are probably not better than that of the current ergometric tests. The choice of an anaerobic test depends on the aims and subjects of a study and its practicability within a testing session.
Partial sleep loss comprises a common source of potential stress. The effects of a nightly ration of 2.5 hr sleep on a battery of psychomotor, physical working capacity and subjective state tests were investigated in a group of trained subjects (n=8) over 3 nights of sleep loss and a single night of subsequent recovery sleep. A 3-day period where normal sleep was permitted was used as a control, the order of control and experimental presentation being counterbalanced. A significant treatment effect was observed for anxiety, hand steadiness, choice reaction time (CRT) preexercise and anaerobic power while grip strength, lung function and endurance capacity were unaffected. Exercise was found to attenuate the effects of sleep loss on CRT. A significant trend over days was found for hand steadiness and reciprocal tapping. All measures except hand steadiness had returned to baseline levels after the recovery night's sleep. It was concluded that one night's sleep of only 2.5 hr has a detrimental effect on psychomotor function but that gross motor functions remain intact for up to 3 nights of partial sleep deprivation.
This study present an easy and practical subjective method for evaluating vigilance disorders: the sleep diary. We used it in hypersomnia and deficits of waking. Sleep diaries were filled in by 10 control and 22 hypersomniac subjects. Twentyfour hour polyhypnographic recording allowed the classification of hypersomnia as 13 narcolepsies, 9 hypersomnias with a prevalence of PS, 2 ‘harmonious’ hypersomnias and 1 waking deficit. The sleep diary data (amount of nocturnal sleep and diurnal sleep onset and vigilance decrease) were compared with polygraphic results. According to the diary data, 3 groups of hypersomnia appeared with regard to the time at which sleep onset occurred. The first group presented an increase of sleep onsets at 2 p.m. In the second group, almost exclusively composed of narcoleptic subjects, sleep onsets occurred every 2 h and in the third group they were distributed throughout the day. These results suggest different physiological mechanisms for these 3 groups of hypersomnia. Finally, the sleep diary seems to be an easy and cheap method of evaluating vigilance disorders in hypersomniac subjects during their everyday life.
The effect of time of day on the neural activation and contractile properties of the human adductor pollicis muscle was investigated in 13 healthy subjects. Two different times of day were chosen, corresponding to the minimum (7 h) and maximum (18 h) levels of strength. The force produced was compared with the associated electromyographic (EMG) activity during voluntary and electrically induced contractions in order to determine whether peripheral or central mechanisms play a dominant role in diurnal force fluctuation. The results indicated that the force produced during a maximum voluntary contraction (MVC) was significantly higher (+8.9%) in the evening than the morning. Since the increase in force of the MVC and the tetanic contraction (100 Hz) were similar, it is suggested that peripheral mechanisms are responsible for diurnal fluctuations in force. This conclusion is supported by the observation that central activation, tested by the interpolated twitch method during an MVC, did not change, and that the EMG was less per unit force in the evening. In addition to the increase in maximum twitch and tetanus force, significant changes in muscle contractile kinetics were also observed. The maximum rate of tension development and the relaxation of the twitch and tetanus increased in the evening, and the twitch contraction time (CT) and the time to half-relaxation (TR1/2) were reduced. Because the mean range of variation in skin temperature (2.6°C) observed over the course of the day was very low, this change cannot entirely explain those observed in muscle contractile properties. © 1999 John Wiley & Sons, Inc. Muscle Nerve 22: 1380–1387, 1999
The number of travellers undertaking long-distance flights has continued to increase. Such flights are associated with travel fatigue and jet lag, the symptoms of which are considered here, along with their similarities, differences, and causes. Difficulties with jet lag because of sleep loss and decreased performance are emphasised. Since jet lag is caused mainly by inappropriate timing of the body clock in the new time zone, the pertinent properties of the body clock are outlined, with a description of how the body clock can be adjusted. The methods, both pharmacological and behavioural, that have been used to alleviate the negative results of time-zone transitions, are reviewed. The results form the rationale for advice to travellers flying in different directions and crossing several time zones. Finally, there is an account of the main problems that remain unresolved.
Anaerobic power and capacity were measured in nine college-age men at four different times of day: 03.00 h, 09.00 h, 15.00 h, and 21.00 h. Modified Wingate tests were performed against a common resistance of 5.5 kg (0.074 +/- 0.004 kg per kg body mass). Peak power was defined as the highest power output during a 5-s period in the test, and anaerobic capacity was defined as the total external work during the 30-s test. Peak power tended to differ across testing times (F = 2.50, p = .10), with the mean at 21.00 h about 8% higher (p less than .05) than at 03.00 h. Anaerobic capacity differed across the times of day (F = 9.58, p less than .01), with the means at 15.00 h and 21.00 h about 5% higher (p less than .05) than at 03.00 h and 09.00 h. These results suggest that there are circadian rhythms in anaerobic power and capacity.
The effect of 60 h of sleep deprivation (SD) upon physical performance and physiological responses to exercise was examined in 11 male subjects. The experiment consisted of two conditions separated by at least 10 d. In the experimental condition (E) subjects remained awake for 60 h and in the control condition (C) the same subjects had 7 h of sleep per night. In both conditions subjects reported to the laboratory on the evening prior to d 1 and slept for 7 h. Physical performance testing was carried out on d 1 and again on d 3 after either two nights of sleep or two nights of SD. Results obtained on d 3 are expressed relative to d 1, the control day. Maximal isometric and isokinetic muscular strength and endurance of selected upper and lower body muscle groups, performance of the Wingate Anaerobic Power Test, simple reaction time, the blood lactate response to cycle exercise at 70% VO2max, and most of the cardiovascular and respiratory responses to treadmill running at 70% and 80% VO2max, were not significantly altered as a result of SD. These results suggest that sleep loss of up to 60 h will not impair the capability for physical work, a finding of considerable importance in sustained military operations which frequently involve the combination of both physical and mental tasks.