On: 05 October 2014, At: 05:18 Publisher: Routledge
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Sports Sciences
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/rjsp20
Sleep in athletes and the effects of Ramadan
Rachida Roky
a, Christopher Paul Herrera
b& Qanta Ahmed
ca
University of Hassan II Ain Chock, Laboratory of Physiology and Molecular Genetics , Km 8 Route d'El Jadida, B.P 5366 Maarif, Casablanca , 20100 , Morocco
b
Aspetar – Qatar Orthopaedic & Sports Medicine Hospital, Research & Education Centre , 1 Sports City St, Po Box 29222, Doha , 00000 , Qatar
c
Attending Sleep Disorders Medicine, Division of Pulmonary Disease and Critical Care Medicine, Department of Medicine , Winthrop University Hospital , New York , United States Published online: 14 Jun 2012.
To cite this article: Rachida Roky , Christopher Paul Herrera & Qanta Ahmed (2012) Sleep in athletes and the effects of Ramadan, Journal of Sports Sciences, 30:sup1, S75-S84, DOI: 10.1080/02640414.2012.693622
To link to this article: http://dx.doi.org/10.1080/02640414.2012.693622
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions
Sleep in athletes and the effects of Ramadan
RACHIDA ROKY
1, CHRISTOPHER PAUL HERRERA
2, & QANTA AHMED
31
University of Hassan II Ain Chock, Laboratory of Physiology and Molecular Genetics, Km 8 Route d’El Jadida, B.P 5366 Maarif, Casablanca, 20100 Morocco,
2Aspetar – Qatar Orthopaedic & Sports Medicine Hospital, Research & Education Centre, 1 Sports City St, Po Box 29222, Doha, 00000 Qatar, and
3Attending Sleep Disorders Medicine, Division of Pulmonary Disease and Critical Care Medicine, Department of Medicine, Winthrop University Hospital, New York, United States
(Accepted 10 May 2012)
Abstract
Sleep is now considered as a new frontier in performance enhancement. This article presents background content on sleep function, sleep needs and methods of sleep investigation along with data on the potential effects of Ramadan fasting on sleep in normal individuals and athletes. Accumulated sleep loss has negative impacts on cognitive function, mood, daytime sleepiness and performance. Sleep studies in athletes fasting during Ramadan are very rare. Most of them have demonstrated that during this month, sleep duration decreased and sleep timing shifted. But the direct relation between sleep changes and performance during Ramadan is not yet elucidated. Objective sleep patterns can be investigated using polysomnography, actigraphy, and standardised questionnaires and recorded in daily journals or sleep logs. The available data on sleep indicate that team doctors and coaches should consider planning sleep schedule and napping; implementing educational programmes focusing on the need for healthy sleep; and consider routine screening for sleep loss in athletes of all age groups and genders.
Keywords: sleep, Ramadan, athletes, sport, fasting
Introduction
Recently, the importance of sleep for athletic performance has been presented in the literature (Mah, Mah, Kezirain, & Dement, 2011; Samuels, 2008). However, sleep remains poorly described in athletes, especially during Ramadan in which sig- nificant diurnal changes are known to occur (Reilly &
Waterhouse, 2007). Indeed, sleep has been recog- nised among coaches and players to be a crucial component for successful training, competition, and recovery (Samuels, 2008). As such, sleep is now considered as a new frontier in performance en- hancement however investigations are only just beginning. Therefore, the primary purpose of this article is to provide a brief review on sleep physiology and its functional importance, to provide a useful summary of the studies reporting on sleep in athletes during Ramadan and its impact on sports perfor- mance and to provide a critical appraisal of the available methodologies which have been used to investigate sleep in athletes. With such an attempt, the aim of this review is to provide a provocative
framework for further research that bridges sleep medicine and sports medicine in order to evaluate the sleep need of athletes and how sleep is related to peak physical performance.
Sleep stages and functional importance
The human sleep wake cycle revolves around an approximate 24 hour time period during which the organism oscillates between behaviourally active (waking) states and behaviourally quiescent (sleep- ing) states.
Behaviourally, sleep involves a perceptual disen- gagement from the surrounding environment and an inability to respond to external stimuli (Carskadon &
Dement, 1994). Yet, sleep is distinguished from coma by its reversibility and intact arousal systems which can trigger termination of sleep in response to substantive physiological stressors or biologic signals.
Sleep can be further characterised by the specific oscillations and morphologic changes in brain wave and eye-movement activity. Such changes allow for the clear identification of sleep stages, numbered as
Correspondence: Rachida Roky, University of Hassan II Ain Chock, Laboratory of Physiology and Molecular Genetics, Km 8 Route d’El Jadida, B.P 5366 Maarif, Casablanca, 20100 Morocco. E-mail: rachidaroky@yahoo.fr.
Journal of Sports Sciences, 2012; 30(S1): S75–S84
ISSN 0264-0414 print/ISSN 1466-447X onlineÓ2012 Taylor & Francis http://dx.doi.org/10.1080/02640414.2012.693622
Downloaded by [University of Delaware] at 05:18 05 October 2014
one to four and one stage termed rapid eye move- ment (REM) sleep (Rechtschaffen & Kales, 1968).
Sleep stages 1–4 are commonly referred to as non- rapid eye movement (NREM) sleep. During the sleep period, NREM and REM sleep are exhibited in regular oscillation with one another in approximately 90–120 minute intervals, though normal human sleep should always begin with NREM sleep and cycle into increasingly longer periods of REM sleep.
Recently, the nomenclature for sleep stages 1–4 was re-classified as N1 to N3 by consolidating the deepest stages of NREM sleep, previously stages 3 and 4 into N3 (Iber, Ancoli-Israel, Chesson, & SF, 2007). Finally, the majority of the sleep period is comprised of light sleep stages N1 and N2 (50%), followed by REM sleep (20–25%), and deep, slow wave sleep N3 (20–25%).
Much about the function of sleep has been examined through the impact of sleep deprivation, specifically partial sleep deprivation on both animal models and the human subject. Although the exact functions of sleep remain controversial (Horne, 1988), NREM sleep is believed to be related to homeostatic processes rejuvenating and replenishing major physiological function. NREM sleep, espe- cially N3 sleep is very much driven by sleep need which is determined by prior duration of wakeful- ness. By contrast, REM sleep does not appear to be driven by sleep need. In fact prior sleep loss is associated with a reduction in REM sleep at the expense of NREM sleep which predominates.
Theories about the function of REM sleep centre on central nervous system development as well as network stabilisation, memory consolidation and healthy psychological functioning (Vassalli & Dijk, 2009). Recent work shows that selective REM sleep loss lowers the pain threshold and results in hyperalgesia in normal human volunteers when presented with fixed painful stimuli, suggesting intact REM sleep may also contain some analgesic properties (Roehrs, Hyde, Blaisdell, Greenwald, &
Roth, 2006).
Human sleep need
Human sleep need varies across the lifespan (Van Dongen, Vitellaro, & Dinges, 2005). The largest database to date evaluated 1.16 million Americans in a self-report survey of average sleep need (Kripke, Garfinkel, Wingard, Klauber, & Marler, 2002). These participants were part of a cohort interviewed from a 1982 American Cancer Society study. While sleep patterns may have changed since this time, important findings are noteworthy.
For example, the study found that most of the general population falls along the median of a regular bell-shaped curve with an approximate 8
hours of total sleep time each night. However, in recent times, especially among many westernised cultures, many in the general population do not attain an 8-hour sleep opportunity. A 2005 Gallop Poll of Americans indicated average total sleep times during week days were in the realm of 6.8 hours daily and extending to 7.4 hours each weekend night, indicating an accumulating sleep debt. These patterns majorly reflect a self-restricted sleep period and are likely to be replicated in all post-industrial societies. Moreover, anecdotally in the authors’ experience, such short sleep times are rapidly arriving in the fast modernising Muslim world particularly within the Arab Gulf Region.
Even when individuals have shortened total sleep times, their recognition of their own sleep deficit is frequently lacking. After 4 days of unrestricted sleep opportunity, participants were extending their habi- tual sleep period by over 4 hours every day, amounting to a 16 hour sleep debt (Roehrs et al., 2006). Notably, the participants had described themselves as short sleepers and denied feeling or being sleep deprived. This is unsurprising since measures of one’s own sleepiness are notoriously difficult for an individual to make and intensely subjective. There are even data to suggest as sleep deprivation increases our perception of sleepiness is further blunted and frequent cognitive errors are presented (Van Dongen, Maislin, Mullington, &
Dinges, 2003).
Sleep need in athletes
The sleep need of athletes remains largely unknown given that the measurement of sleep in athletes is not common. Recently, investigators raised the question as to whether the notion of a sleep debt would be applicable to athletes and whether increased amounts of sleep could enhance athletic performance. In- vestigators at Stanford University answered this question by studying 11 healthy students on the university basketball team (Mah et al., 2011). Parti- cipants were first asked to follow their habitual sleep period (e.g. an 8 hour sleep period) and then were subsequently asked to voluntarily extend their total sleep time with a minimum goal of a 10 hour sleep period for a five to seven week period. The participants were found to have enhanced basketball performance by all measures after habitual sleep extension. Total sleep times increased by approxi- mately two hours and participants were shown to sprint faster and have greater shooting accuracy than their baseline performance. Alertness also improved, as did mood, sleepiness and fatigue, leading the investigators to conclude that optimising sleep need, or reaching sleep satiation was likely to have a positive impact on measured athletic performance.
Downloaded by [University of Delaware] at 05:18 05 October 2014
In adolescents, adequate sleep appears also to have a major influence on the ability of an athlete to exert effort (Engle-Friedman, Palencar, & Riela, 2010).
Adolescent athletes were found to be sleep deprived during the week when they were attending practice before and after school. This finding intensified as adolescence advanced – the older athletes slept less than the younger athletes. Those who subjectively experienced more night time awakenings selected less challenging manometers during their practices.
Investigators found that total sleep time correlated negatively with the perceived difficulty of selected manoeuvres. The authors concluded that sleep loss therefore directly predicted the proportional increase in the perception of difficulty.
In summary, in athletes sleep loss is an important factor in determining not only how well a task is completed, as the basketball study would indicate, but also the athlete’s own perception of their ability to perform habitual training tasks. Therefore, given that sleep restriction is often self imposed, sleep is likely a modifiable factor influencing not only performance but also motivation.
Effects of Ramadan on sleep and performance in athletes
There is no substantive evidence for major effects on general health during Ramadan across the studies in the literature (reviewed in Roky, Houti, Moussamih, Qotbi, & Aadil, 2004). However, Ramadan inter- mittent fasting induces an important effect on sleep.
Most of the studies on sleep and Ramadan were conducted in non-athlete populations and they generally reported a delay in sleep time and a reduction in sleep duration. Using sleep question- naires, two studies (Laraqui et al., 2001; Taoudi, Roky, Toufiq, Benaji, & Hakkou, 1999) have reported in young adults and workers that the percentage of people who went to sleep after midnight increased during Ramadan, as compared to the month before. Sleep duration was 56 hours in 68% of the workers during Ramadan but only 37%
before Ramadan (Laraqui et al., 2001). Using polysomnography recordings in laboratory condi- tions, Roky, Chapotot, Hakkou, Benchekroun, and Buguet (2001) observed that several sleep para- meters changed during this month. These authors showed that sleep latency increased (19.2 min vs.
58.1 min before and during Ramadan respectively) and total sleep time decreased (422 min vs. 383 min before and during Ramadan respectively) during Ramadan (Roky et al., 2001). Sleep architecture also changed since the proportion of NREM sleep increased during Ramadan, particularly stage 2 (50.2% vs. 55% before and during Ramadan respectively) while REM sleep duration decreased
(22.7% vs. 19.4% before and during Ramadan respectively). Moreover, sleep schedules noted by the participants throughout the 2-month investiga- tion showed a 1 hour delay in sleep time. This delay in sleep onset and the alleviation of sleep were associated with an increase in nocturnal body temperature possibly due to later meal times (Roky et al., 2001).
Sleep changes during Ramadan were also reported in non-fasting participants suggesting that factors other than fasting may play an important role in modifying an individual’s behaviour during Rama- dan (BaHammam, 2005). These factors could be related to social and spiritual activities. In contrast, the same group demonstrated, using an actigraphy device, that nocturnal total sleep time did not change during Ramadan, and that the 24 hour sleep opportunity (total sleep time þ nap time) was longer during Ramadan than in the baseline period (Ba- Hammam, Alrajeh, Albabtain, BaHammam, &
Sharif, 2010).
Sleep metrics in athletes during Ramadan are not homogenous (Table I). Studies have demonstrated that sleep decreased during Ramadan by *60 min in football players undertaking their usual training and match schedule during this month (Leiper, Junge, Maughan, Zerguini, & Dvorak, 2008), by
*88 min in middle-distance athletes (Chennaoui et al., 2009), and by *30 min in football players (Zerguini et al., 2008). In a recent study conducted in football athletes from Morocco, sleep time was delayed by 3 hours and sleep duration decreased by a half-hour during Ramadan (Roky, Herrera, Farooq, & Gaoua, 2011). The subjective sleep quality also decreased significantly. In addition, Herrera, Lippert, and Sas (2011) found that the average total sleep time before Ramadan (6.5 hours) was considerably low and was significantly reduced at the end of Ramadan (5.5 hours) in football players. Knowing that sleep onset is triggered by a rapid decrease in core temperature, the maximum rate of decline being observed 60 min before sleep onset (Murphy & Campbell, 1997), it could be suggested that the delayed sleep period and decreased total sleep time during Ramadan could be related to the delay in consumption of nocturnal meals and delay in nocturnal training or competi- tions which would similarly present a thermogenic effect on core body temperature. In contrast to these findings, others studies demonstrated no significant change in sleep duration in adolescent soccer players (Meckel, Ismaeel, & Eliakim, 2008) and in power athletes (Karli, Guvenc, Aslan, Hazir,
& Acikada, 2007). The heterogeneity concerning the effects of Ramadan on sleep in athletes could be related to differences in methodology, population, or to potential unidentified cultural differences.
Sleep in athletes and the effects of Ramadan S77
Downloaded by [University of Delaware] at 05:18 05 October 2014
Finally, daytime cognitive functioning is signifi- cantly impaired during Ramadan in non-athletes. In sedentary healthy subjects, subjective alertness, evaluated by the visual analogue scale, decreased at 9:00 and 16:00 h and increased at 23:00 h. Daytime sleepiness measured by the multiple sleep latency test increased particularly at 10:00, 12:00 and 16:00 h (Roky et al., 2003). Similarly, sleep deprivation associated with Ramadan negatively influenced mood (Roky, Iraki, HajKhlifa, Lakhdar Ghazal, &
Hakkou, 2000). Unfortunately, to date, daytime sleepiness, and cognitive function have not been systematically measured in athletes.
Measurement of sleep in athletes: A review of current methods and literature
Several methods have been used to examine sub- jective components of sleep in athletes, though the studies during Ramadan have relied exclusively on sleep logs (Table II). Unfortunately, sleep logs vary which results in reduced reliability and difficulty when comparing results between studies. In contrast, standardised sleep questionnaires provide widely documented psychometric properties and therefore improved validity. It should be highlighted that polysomnography (PSG) and actigraphy remain superior methods to describe sleep objectively in athletes but have not been used in studies during Ramadan.
Subjective assessment of sleep Sleep logs
Sleep logs are practical and can easily assess self- reported estimates of quantitative sleep measures (e.g. total sleep time, sleep onset latency, time in bed period). Unfortunately, data from sleep logs have been shown to poorly correlate with objective measurement of sleep in athletes (Richmond, Daw- son, Hillman, & Eastwood, 2004). In particular, the reliability to detect changes in sleep quality and to a lesser extent sleep duration is poor given incon- sistencies in the included scales and measurement
techniques. For example, among the studies con- ducted during Ramadan, sleep quality was deter- mined using a 3- or 4-term categorical scale (Leiper et al., 2008; Zerguini et al., 2008), inferred via changes in sleep timings (Aziz, Wahid, Png, &
Jesuvadian, 2010; Chennaoui et al., 2009) or was not explicitly assessed (Karli et al., 2007; Meckel et al., 2008). Moreover, assessment of total sleep time was uniform; for example, data were collected by self-report (Aziz et al., 2010; Chennaoui et al., 2009; Leiper et al., 2008), a coach (Meckel et al., 2008) or a research technician (Zerguini et al., 2008). Therefore, sleep logs should be combined with another measurement technique to improve the validity of the results.
Standardised sleep questionnaires
The Pittsburgh Sleep Quality Index is validated to assess self-reported sleep patterns and distinguish persons with clinical sleep disturbances (Buysse, Reynolds, Monk, Berman, & Kupfer, 1989). The Pittsburgh Sleep Quality Index consists of 19 questions which are grouped into seven components: sleep quality, sleep latency, sleep duration, sleep efficiency, sleep disturbances, the use of sleeping medications, and daytime dysfunc- tion. The total score for the Pittsburgh Sleep Quality Index is between 0–21, and higher scores indicate more severe sleep difficulties. A Pittsburgh Sleep Quality Index score of 5 is considered to indicate poor sleep quality, although a more conservative threshold of 8 has also been used (Buysse, Ancoli-Israel, Edinger, Lichstein, &
Morin, 2006). In addition, the Pittsburgh Sleep Quality Index has added research value given its availability in several languages (e.g. Arabic) and the fact that quantitative variables (e.g. sleep onset latency, total sleep time, and sleep efficiency) can be obtained.
Studies using the Pittsburgh Sleep Quality Index to evaluate sleep in athletes during Ramadan are rare. Herrera et al. (2011) reported that *50% of Muslim football players had a Pittsburgh Sleep Quality Index score 5 at baseline and at the end
Table I. Summary of the studies about sleep in athletes during Ramadan.
Total sleep time before Ramadan
Total sleep time during Ramadan
Average change in total
sleep time & quality Number of Players Study 8.4 hours 8.2 hours -30 min; reduced sleep quality 55 football players Zerguini et al., 2008 (not available) (not available) -60 min; no change in sleep quality 54 football players Leiper et al., 2008
8.6 hours 8.6 hours No change; no change 19 football players Meckel et al., 2008
7.3 hours 5.8 hours -88 min; no change in sleep quality 8 runners Chennaoui et al., 2009
8.3 hours 9.2 hours No change; no change 10 power athletes Karli et al., 2007
6.5 hours 5.5 hours -60 min; no change in sleep quality 9 football players Herrera et al., 2011
Downloaded by [University of Delaware] at 05:18 05 October 2014
of Ramadan. These data appear somewhat consistent with reports from non-Muslim junior and profes- sional athletes; more than 85% of adolescent and 75% of adult Canadian athletes had a Pittsburgh Sleep Quality Index of 5 (Samuels, 2008). Taken together, these studies suggest that a substantial number of the athletes may suffer from poor sleep quality and would benefit from further evaluation (Samuels, 2008). The Pittsburgh Sleep Quality Index therefore may be of substantial value for coaches and clubs who want to quickly determine habitual sleep habits in athletes and to evaluate for the possibility of clinical sleep disturbances.
Additional standardised questionnaires were used to evaluate sleep quality in athletes but not during Ramadan. The Leeds Sleep Evaluation Question- naire (Parrott & Hindmarch, 1980) was used to study sleep quality in athletes during exposure to a
hypoxic tent (Pedlar et al., 2005). More recently two
‘sport specific’ questionnaires were developed to assess sleep quality as a component of recovery and stress or overtraining. The Recovery-Stress Ques- tionnaire for Athletes provides a useful measurement of the extent that an athlete is physically and/or mentally stressed and strategies for recovery (Kell- man & Kallus, 2001). The Recovery-Stress Ques- tionnaire for Athletes includes a component score for sleep quality and has been utilised in a few athlete populations (Brink, Visscher, Coutts, & Lemmink, 2010; Coutts & Reaburn, 2008; Jurlmae, Maestu, Purge, & Jurimae, 2004; Jurlmae, Maestu, Purge, Jurimae, & Soot, 2002). Similarly, the Multi- component Training Distress Scale was developed to assess sleep quality as a symptom of overreaching and overtraining (Main et al., 2010; Main & Grove, 2009). To our knowledge these instruments have not
Table II. Summary of current methods and available studies describing subjective sleep, daytime sleepiness, and chronotype in athletes.
Category Test (acronym) Assessment Available studies; first author only
Sleep logs Non-specific set of questions subjective estimates of: total sleep time, bedtime and rise time, sleep latency, time in bed; sleep quality has been inferred in various ways
Taylor 1997; Atkinson 2001; Reilly 2001; Cardinali 2002; Booth 2006;
Karli 2007;Meckel 2008;Zer- guini 2008;Chennaoui 2009;
Engle-Friedman 2010;Aziz 2010;
Gerber 2011 Categorical scales sleep quality using either 3- or 4-
anchor terms
Richmond 2004, 2007;Leiper 2008;
Zerguini 2008
Likert type scale sleep quality using 7-pt scale Al Haddad 2011
Visual analogue scale (VAS) sleep quality and daytime sleepiness using 100 mm equivalent scale with varied anchor terms
Polak 1993; Cardinali 2002; Tafti 1992
Standardised questionnaires
Pittsburgh Sleep Quality Index (PSQI) global scores for sleep quality and 7 component scores; also provides for identification of self-reported quantitative measures
Adam 2004; Samuels 2008; Fietze 2009; Modolo 2011; Bigelman 2011;Herrera 2011; Silva 2012 Leeds Sleep Evaluation Questionnaire
(LSEQ)
global and individual component scores for sleep quality using mul- tiple 100 mm VAS
Montmayeur 1994
Recovery-Stress Questionnaire for Ath- letes (REST-Q)
sleep quality as a component of recovery and stress
Pedlar 2005 Multi-component Training Distress Scale
(MTDS)
sleep quality as a component of over- reaching or overtraining syndrome
Jurlmae 2002, 2004; Coutts 2008;
Brink 2010 Stanford Sleepiness Scale (SSS) daytime sleepiness using 7-pt Likert
type scale; can be used for moment- by-moment changes
Tafti 1992; Blumert 2007; Engle- Friedman 2010
Karolinska Sleepiness Scale (KSS) daytime sleepiness using 9-pt Likert type scale; can be used for moment- by-moment changes
Aziz 2010
Epworth Sleepiness Scale (ESS) ‘excessive daytime sleepiness’ using 8 questions rated on the chances of falling asleep in habitual daily si- tuations
Fietz 2009, Modolo 2011; Silva 2012;
Herrera 2011
Morningness-Eveningness Questionnaire (MEQ)
chronotype using 19-item question- naire; categories include morning-, evening-, or neither- type
Silva 2012;Roky 2011
Athletes Morningness-Eveningness Scale (AMES)
chronotype using 4-item question- naire; has not been validated
Samuels 2008
*boldedreferences denote that a study was conducted during Ramadan
Sleep in athletes and the effects of Ramadan S79
Downloaded by [University of Delaware] at 05:18 05 October 2014
been validated against the Pittsburgh Sleep Quality Index or other forms of objective sleep measurement.
A few studies have also explored the construct of daytime sleepiness in athletes. Concerning Rama- dan, Aziz et al. (2010) failed to demonstrate a change in daytime sleepiness among 10 moderately trained runners who participated in an experimental exercise session. This study used the Karolinska Sleepiness Scale, a validated method to detect the current level of daytime sleepiness using a single 7- point Likert scale (Kaida et al., 2006). In contrast, the Epworth Sleepiness Scale was developed to assess the propensity of daytime sleepiness in usual daily situations (Johns, 1991). The Epworth Sleepi- ness Scale consists of eight questions in which a response between 1 and 3 is recorded; a higher score is reported when the chance of falling asleep is greater. A cut-off score of 8 has been used to suggest excessive daytime sleepiness (Kumar, Bhatia, &
Behari, 2003). Herrera et al. (2011) reported among nine Muslim football players that the average score on the Epworth Sleepiness Scale was within normal range at baseline (Epworth Sleepiness Scale ¼ 6) and did not significantly change at the end of Ramadan (Epworth Sleepiness Scale ¼ 8). Given the paucity of literature and small sample sizes in these studies, a larger study is required before a conclusion can be made regarding the presence of daytime sleepiness in athletes during Ramadan.
Finally, chronotype refers to an individual’s pre- ference for ‘morning’ vs. ‘evening’ type activity (Horne & Ostberg, 1976) and was investigated in a single study during Ramadan. Roky et al. (2011) presented data from Muslim football players (18–35 years) indicating that *71% of athletes were
‘morning’ type before Ramadan versus 61% at the end of Ramadan. Interestingly, most athletes pre- ferred training at the end of the day, after 19:00, both before and at the end of Ramadan (64% and 84%, respectively). These were not statistically significant and therefore only preliminary. However, in non- athletes, Ramadan has been shown to induce a phase
delay in circadian rhythm and sleep timings of up to 2–4 hours (Roky et al., 2004). Interestingly, this degree of shift has been shown to alter the time of peak performance in elite athletes (Javierre et al., 1996). Thus, disturbances to the circadian timing of the sleep-wake cycle – either from extended jet travel, social commitments, daily stress, or those associated with Ramadan – may present physiological or psychological challenges that if not overcome will impede on athletic performance (Reilly & Edwards, 2007). Thus, chronotype and the time preference for training in football players carries practical implica- tions for sport.
Objective measurement of sleep Polysomnography
Polysomnography is considered the ‘gold-standard’
procedure to assess objective sleeping patterns but has not been used in athletes during Ramadan (Table III). Polysomnography is used to diagnose and evaluate treatment of sleep disorders and provides the most comprehensive measurement of sleep behaviour during research protocols (Kushida et al., 2005). During polysomnography, differential electrical potentials collected through scalp and skin surface electrodes are recorded to measure electro- encephalographic activity and additional physiologic measures such as: eye movement activity, skeletal muscle activity – typically of the masseter and anterior tibialis – breathing, respiratory effort, snor- ing, and plethysomnography. This combination of signals allows for the identification of sleep stages, periodic limb movements, sleep disordered breath- ing, and oxygen desaturations. Unfortunately, given the requirement for specialised technical staff who are needed for both acquisition and scoring of sleeping patterns, the time required to complete testing procedures (e.g. 1 hour setup and 48 hours recording time), and the disturbances from the electrodes, polysomnography investigations are
Table III. Summary of current methods and available studies describing objective sleeping patterns in athletes.
Test (acronym) Assessment Available studies; first author only
Polysomnography (PSG) Sleep duration and quality using com- prehensive physiologic assessment of brain wave activity, breathing, muscle movement, and oxygenation; analysed by qualified technician
Mougin 1991, 1992, 1992, 2001; Mon- tmayeur 1994; Taylor 1997; Netzer 2001; Kinsman 2002, 2003, 2005;
Pedlar 2005; Hoshikawa 2007, 2010;
Leger 2008; Gosselin 2009; Davies 2010
Actigraphy sleep duration and quality using move-
ment activity collected from wrist device and analysed using software
Straub 2001; Wall 2003; Mauvieux 2003;
Richmond 2004, 2007; Montaruli 2009; Fietze 2009; Pontifex 2010; Mah 2011
Downloaded by [University of Delaware] at 05:18 05 October 2014
underutilised in athletes, except in controlled, laboratory experiments (see references in Table III).
Noteworthy, Baekland and Lasky (1966) were among the first to report on polysomnography in athletes and demonstrated a positive relationship between exercise and the amount of slow wave sleep.
This study highlights the main advantage of poly- somnography, the ability to determine the distribu- tion of sleep stages and therefore examine relationships with either performance or recovery.
In a different light, Leger et al. (2008) used ambulatory polysomnography techniques to describe the sleep pattern of professional sailors before and during competition. In this study the encumbrances associated with traditional polysomnography were minimised while at sea by using one of two ambulatory polysomnography systems that were capable of recording sleep stages but not breathing or oxygenation. Thus, given the increasing avail- ability of such ambulatory polysomnography sys- tems, this study highlights their potential use in a sport setting.
Actigraphy
Actigraphy devices are placed on the wrist and record movement data which can be analysed using specialised software to estimate sleep quantity and sleep quality (Ancoli-Israel et al., 2003). Specifically, each 1-minute data segment is quantified as either asleep or awake, and the total time asleep is recorded. Sleep quality is indicated by the number of awakenings and sleep efficiency – the ratio of time spent asleep to the total sleep period. Although sleep stages cannot be ascertained using actigraphy, it offers substantial benefits over polysomnography procedures; namely its ease of use, cost-effectiveness, and ability to record continuous data for periods up to one month. As such, the use of actigraphy increases the temporal resolution of objectively assessed sleeping patterns. This may provide for greater insight among athletes during extended periods of training or competition, to investigate symptoms of jet-lag after transmeridian flights, or to investigate sleep in athletes during Ramadan, which lasts for *30 days.
Despite these methodological improvements, there are no studies using actigraphy among athletes during Ramadan. In fact, studies using actigraphy are less common than polysomnography studies and normative data have only recently been published.
Mah et al. (2011), who demonstrated improvements in specific measures of basketball performance after a 5–7 week sleep extension, reported using actigraphy that the athletes slept an average of 110 min more when compared to baseline. A similar study using actigraphy could be developed to assess the impact of
an extended sleep period on sleep and performance in athletes during Ramadan.
Thus, for the future studies regarding sleep during Ramadan, sleep logs should be used in combination with standardised sleep questionnaires to improve validity and in combination with actigraphy to assess both subjective and objective sleeping patterns in athletes. Polysomnography is required to investigate the mechanistic links be- tween sleep loss (and sleep extension) and sports performance and recovery.
Conclusion
Many people are unaware of their individual sleep need and the consequences of sleep loss on performance and health. During Ramadan, noctur- nal sleep duration decreases and sleep time is delayed, which may have effects on daytime perfor- mance. By teaching coaches, sports physicians, players and executives the importance of sleep, the methods used to assess sleep behaviour, and the influence of sleep on exercise, many of the knowl- edge deficits can be corrected, not only with an impact on performance but also major impacts on long term health and wellness. Collaborative re- search between the fields of sports medicine and sleep medicine with an aim of deepening the under- standing of sleep’s bidirectional impact on exercise is recommended.
Recommendations for healthy sleep in athletes during Ramadan
Recommendation 1. The athlete’s sleep schedule should be individualised based on chronotype.
Morning types have preference for earlier sleep time and evening types have preference for later sleep time. Plan a sleep schedule to make sure that athletes get a sufficient amount of sleep – at least 7–8 hours across a 24 hour period.
Recommendation 2. During Ramadan the nocturnal sleep period will likely be delayed and shortened due to changes in training and meal times (e.g. Sohour which is taken just before sunrise). Planned naps for 20–30 minutes can significantly improve alertness whereas longer naps of approximately 90 minutes may be necessary to repay accumulated sleep debt.
Vigorous exercise and complex coordinated move- ments should not be planned within 1 hour after a longer nap as ‘sleep inertia’ – a state of subjective drowsiness and reduced motor dexterity – may be present.
Recommendation 3. Athletes and coaches should be educated on the sleep need of athletes, the impact of nocturnal meals and physical activity, on sleep, and on situations known to exacerbate sleep loss such as Sleep in athletes and the effects of Ramadan S81
Downloaded by [University of Delaware] at 05:18 05 October 2014
pre- and post-competition insomnia. For example, it may be useful to omit or reduce the intensity of morning training sessions after such occasions to improve recovery.
Recommendation 4. General educational pro- grammes focusing on sleep hygiene should be made available to all athletes, coaches, and trainers to improve sleep habits on an annual basis, each season.
Recommendation 5. Develop educational pro- grammes focusing on the need for sleep during Ramadan and the impact of nocturnal meals and physical activity on sleep timing. Education pro- grammes could focus on the impact of sleep deprivation on performance and the opportunity to use sleep as a performance enhancer. Also, give access to a board certified, fellowship trained, sleep specialist to all football/athletic clubs and plan routine screening for sleep loss in players, coaches and support personnel.
References
Adam, M. U., Brassington, G. S., Steiner, H., & Matheson, G. O.
(2004). Psychological factors associated with performance- limiting injuries in professional ballet dancers.Journal of Dance Medicine and Science,8, 43–46.
Al Haddad, H., Parouty, J., & Buchheit, M. (2011). Effect of daily cold water immersion on heart rate variability and subjective ratings of well-being in highly trained swimmers.International Journal of Sports Physiology and Performance, PMID: 21941017.
Ancoli-Israel, S., Cole, R., Alessi, C., Chambers, M., Moorcroft, W., & Pollak, C. P. (2003). The role of actigraphy in the study of sleep and circadian rhythms.Sleep,26, 342–392.
Atkinson, G., Buckley, P., Edwards, B., Reilly, T., & Waterhouse, J. (2001). Are there hangover-effects on physical performance when melatonin is ingested by athletes before nocturnal sleep?
International Journal of Sports Medicine,22, 232–234.
Aziz, A. R., Wahid, M. F., Png, W., & Jesuvadian, C. V. (2010).
Effects of Ramadan fasting on 60 min of endurance running performance in moderately trained men.British Journal of Sports Medicine,44, 516–521.
Baekeland, F., Lasky, R. (1966). Exercise and sleep patterns in college athletes.Perceptual & Motor Skills,23, 1203–1207.
BaHammam, A. (2005). Assessment of sleep patterns, daytime sleepiness, and chronotype during Ramadan in fasting and nonfasting individuals.Saudi Medical Journal,26, 616–622.
BaHammam, A., Alrajeh, M., Albabtain, M., BaHammam, S., &
Sharif, M. (2010). Circadian pattern of sleep, energy expendi- ture, and body temperature of young healthy men during the intermittent fasting of Ramadan.Appetite,54, 426–429.
Bigelman, K. A., Chapman, D. P., Freese, E. C., Trilk, J. L., &
Cureton, K. J. (2011). Effects of 6 weeks of quercetin supplementation on energy, fatigue, and sleep in ROTC cadets.
Military Medicine,176, 565–572.
Blumert, P. A., Crum, A. J., Ernsting, M., Volek, J. S., Hollander, D. B., Haff, E. E., Haff, G. G. (2007). The acute effects of twenty-four hours of sleep loss on the performance of national- caliber male collegiate weightlifters. Journal of Strength and Conditioning Research,21, 1146–1154.
Booth, C. K., Probert, B., Forbes-Ewan, C., & Coad, R. A.
(2006). Australian army recruits in training display symptoms of overtraining.Military Medicine,171, 1059–1064.
Brink, M. S., Visscher, C., Coutts, A. J., & Lemmink, K. A.
(2010). Changes in perceived stress and recovery in over- reached young elite soccer players. Scandinavian Journal of Medicine and Science in Sports, 22, 285–292.
Buysse, D. J., Reynolds, C. F., Monk, T. H., Berman, S. R., Kupfer, D. J. (1989). The Pittsburgh Sleep Quality Index: a new instrument for psychiatric practice and research.Psychiatry Research, 28, 193–213.
Buysse, D. J., Reynolds, C. F., 3rd, Monk, T. H., Berman, S. R.,
& Kupfer, D. J. (1989). The Pittsburgh Sleep Quality Index: A new instrument for psychiatric practice and research.Psychiatry Research,28, 193–213.
Cardinali, D. P., Bortman, G. P., Liotta, G., Perez Lloret, S., Albornoz, L. E., Cutrera, R. A., Ortega-Gallo, P. (2002). A multifactorial approach employing melatonin to accelerate resynchronization of sleep-wake cycle after a 12 time-zone westerly transmeridian flight in elite soccer athletes.Journal of Pineal Research,32, 41–46.
Carskadon, M. A., & Dement, W. C. (1994).Principles and practice of sleep medicine(2nd ed.). Philadelphia, PA: W.B. Saunders.
Chennaoui, M., Desgorces, F., Drogou, C., Boudjemaa, B., Tomaszewski, A., Depiesse, F., et al. (2009). Effects of Ramadan fasting on physical performance and metabolic, hormonal, and inflammatory parameters in middle-distance runners.Applied Physiology, Nutrition, and Metabolism,34, 587–
594.
Coutts, A. J., & Reaburn, P. (2008). Monitoring changes in rugby league players’ perceived stress and recovery during intensified training.Perceptual & Motor Skills,106, 904–916.
Davies, D. J., Graham, K. S., & Chow, C. M. (2010). The effect of prior endurance training on nap sleep patterns. International Journal of Sports Physiology and Performance,5, 87–97.
Engle-Friedman, M., Palencar, V., & Riela, S. (2010). Sleep and effort in adolescent athletes.Journal of Child Health Care, 14, 131–141.
Fietze, I., Strauch, J., Holzhause, M., Glos, M., Theobald, C., Lehnkering, H., Penzel, T. (2009). Sleep quality in professional ballet dancers.Chronobiology International,26, 1249–1262.
Gerber, M., Holsboer–Trachsler, E., Puhse, U., & Brand, S.
(2011). Elite sport is not an additional source of distress for adolescents with high stress levels.Perceptual and Motor Skills, 112, 581–599.
Gosselin, N., Lassonde, M., Petit, D., Leclerc, S., Mongrain, V., Collie, A., Montplaisir, J. (2009). Sleep following sport–related concussions.Sleep Medicine,10, 35–46.
Herrera, C. P., Lippert, C., & Sas, B. (2011).Influence of Ramadan on Subjective Sleep Quality and Daytime Alertness in Post- Operative Athletes: A Pilot Study. Paper presented at the APSS Sleep Conference, Minneapolis, MN, USA.
Horne, J. (1988).Why we sleep: The function of sleep in humans and other mammals. New York, NY: Oxford University Press.
Horne, J. A., & Ostberg, O. (1976). A self-assessment question- naire to determine morningness-eveningness in human circa- dian rhythms.International Journal of Chronobiology,4, 97–110.
Hoshikawa, M., Uchida, S., Sugo, T., Kumai, Y., Hanai, Y., &
Kawahara, T. (2007). Changes in sleep quality of athletes under normobaric hypoxia equivalent to 2,000–m altitude: A poly- somnographic study.Journal of Applied Physiology,103, 2005–
2011.
Hoshikawa, M., Uchida, S., Sugo, T., Kumai, Y., Hanai, Y., &
Kawahara, T. (2010). Sleep quality in athletes under normobaric hypoxia equivalent to 1500 m altitude: A polysomnographic study. European Journal of Sports Science, 10, 191–198.
Iber, C., Ancoli-Israel, S., Chesson, A., & SF, Q. (2007).The AASM manual for the scoring of sleep and associated events: Rules, terminology and technical specifications(1st ed.). Westchester, IL:
American Academy of Sleep Medicine.
Downloaded by [University of Delaware] at 05:18 05 October 2014
Javierre, C., Calvo, M., Dı´ez, A., Garrido, E., Segura, R., Ventura, J. L. (1996). Influence of sleep and meal schedules on performance peaks in competitive sprinters. International Journal of Sports and Medicine,17, 404–408.
Johns, M.W. (1991). A new method for measuring daytime sleepiness: The Epworth sleepiness scale.Sleep,14, 540–545.
Jurlmae, J., Maestu, J., Purge, P., & Jurimae, T. (2004). Changes in stress and recovery after heavy training in rowers.Journal of Science and Medicine in Sport,7, 335–339.
Jurlmae, J., Maestu, J., Purge, P., Jurimae, T., & Soot, T. (2002).
Relations among heavy training stress, mood state, and performance for male junior rowers.Perception and Motor Skills, 95, 520–526.
Kaida, K., Takahashi, M., Akerstedt, T., Nakata, A., Otsuka, Y., Haratani, T., Fukasawa, K. (2006). Validation of the Kar- olinska sleepiness scale against performance and EEG variables.
Clinical Neurophysiology,117, 574–581.
Karli, U., Guvenc, A., Aslan, A., Hazir, T., & Acikada, C. (2007).
Influence of Ramadan fasting on anaerobic performance and recovery following short time high intensity exercise.Journal of Sports Science and Medicine,6, 490–497.
Kellman, M., & Kallus, K.W. (2001). Description of The Recovery-Stress Questionnaire for Athletes. In: Recovery-stress questionnaire for athletes. Champaign, IL: Human Kinetics, 5–
10.
Kinsman, T.A., Hahn, A.G., Gore, C.J., Martin, D.T., & Chow, C.M. (2003). Sleep quality responses to atmospheric variation:
Case studies of two elite female cyclists.Journal of Science and Medicine in Sport,6, 436–442.
Kinsman, T.A., Hahn, A.G., Gore, C.J., Wilsmore, B.R., Martin, D.T., & Chow, C.M. (2002). Respiratory events and periodic breathing in cyclists sleeping at 2,650-m simulated altitude.
Journal of Applied Physiology,92, 2114–2118.
Kinsman, T.A., Townsend, N.E., Gore, C.J., Hahn, A.G., Clark, S.A., Aughey, R.J., Chow, C.M. (2005). Sleep disturbance at simulated altitude indicated by stratified respiratory disturbance index but not hypoxic ventilatory response.European Journal of Physiology,94, 569–575.
Kripke, D.F., Garfinkel, L., Wingard, D.L., Klauber, M.R., &
Marler, M.R. (2002). Mortality associated with sleep duration and insomnia.Archives of General Psychiatry,59, 131–136.
Kumar, S., Bhatia, M., & Behari, M. (2003). Excessive daytime sleepiness in Parkinson’s disease as assessed by Epworth Sleepiness Scale (ESS).Sleep Medicine,4, 339–342.
Kushida, C.A., Littner, M.R., Morgenthaler, T., Alessi, C.A., Bailey, D., Coleman, J., Jr., et al. (2005). Practice parameters for the indications for polysomnography and related proce- dures: An update for 2005.Sleep,28, 499–521.
Laraqui, C.H., Tripodi, D., Laraqui, O., Rahhali, A., Caubet, A., Daudi, F., et al. (2001). The effects of fasting and of the quality of sleep on work during the month of Ramadan.
Archives des Maladies Professionnelles de Medecine du Travail, 62, A115–120.
Leger, D., Elbaz, M., Raffray, T., Metlaine, A., Bayon, V., &
Duforez, F. (2008). Sleep management and the performance of eight sailors in the Tour de France A˜ la voile yacht race.Journal of Sports Sciences,26, 21–28.
Leiper, J., Junge, A., Maughan, R., Zerguini, Y., & Dvorak, J.
(2008). Alteration of subjective feelings in football players undertaking their usual training and match schedule during the Ramadan fast.Journal of Sports Sciences,26(Suppl. 3), S55–69.
Mah, C.D., Mah, K.E., Kezirain, E.J., & Dement, W.C. (2011).
The effects of sleep extension on the athletic performance of collegiate basketball players.Sleep,34, 943–950.
Main, L.C., Dawson, B., Heel, K., Grove, J.R., Landers, G.J., &
Goodman, C. (2010). Relationship between inflammatory cytokines and self–report measures of training overload.
Research in Sports Medicine,18, 127–139.
Main, L.C., & Grove, J.R. (2009). A multi-component assessment model for monitoring training distress among athletes. Eur- opean Journal of Sport Science,9, 195–202.
Mauvieux, B., Gouthiere, L., Sesboue, B., & Davenne, D. (2003).
A study comparing circadian rhythm and sleep quality of athletes and sedentary subjects engaged in night work.
Canadian Journal of Applied Physiology,28, 831–887.
Meckel, Y., Ismaeel, A., & Eliakim, A. (2008). The effect of the Ramadan fast on physical performance and dietary habits in adolescent soccer players.European Journal of Applied Physiol- ogy,102, 651–657.
Modolo, V.B., Antunes, H.K., Gimenez, P.R., Santiago, M.L., Tufik, S., & Mello, M.T. (2011). Negative addiction to exercise: Are there differences between genders?Clinics (Sao Paulo),66, 255–260.
Montaruli, A., Roveda, E., Calogiuri, G., La Torre, A., &
Carandente, F. (2009). The sportsman readjustment after transcontinental flight: A study on marathon runners.Journal of Sports Medicine and Physical Fitness,49, 372–381.
Montmayeur, A., Buguet, A., Sollin, H., & Lacour, J.R. (1994).
Exercise and sleep in four African sportsmen living in the Sahel. A pilot study. International Journal of Sports Medicine, 15, 42–45.
Mougin, F., Bourdin, H., Simon-Rigaud, M.L., Nguyen, N.U., Kantelip, J.P., & Davenne, D. (2001). Hormonal responses to exercise after partial sleep deprivation and after a hypnotic drug-induced sleep.Journal of Sports Sciences,19, 89–97.
Mougin, F., Simon-Rigaud, M.L., Davenne, D., Bourdin, H., Guilland, J.C., Kantelip, J.P., Magnin, P. (1992). Tolerance to exertion after sleep reduction and after taking a hypnotic:
Zolpidem. Archives Internationales de Physiologie, Biochimistry, and Biophysiologie,100, 255–262.
Mougin, F., Simon-Rigaud, M.L., Davenne, D., Renaud, A., Garnier, A., Kantelip, J.P., et al. (1991). Effects of sleep disturbances on subsequent physical performance. European Journal of Applied Physiology and Occupational Physiology, 63, 77–82.
Mougin, F., Simon-Rigaud, M.L., Mougin, C., Bourdin, H., Jacquier, M.C., Henriet, M.T., et al. (1992). Met-enkephalin, beta-endorphin and cortisol responses to sub-maximal exercise after sleep disturbances.European Journal of Applied Physiology and Occupational Physiology,64, 371–376.
Murphy, P.J. & Campbell, S.S. (1997). Night-time drop in body temperature: a physiological trigger for sleep onset?Sleep, 2, 505–511.
Netzer, N.C., Kristo, D., Steinle, H., Lehmann, M., & Strohl, K.P. (2001). REM sleep and catecholamine excretion: a study in elite athletes.European Journal of Applied Physiology,84, 521–
526.
Parrott, A.C., & Hindmarch, I. (1980). The Leeds Sleep Evaluation Questionnaire in psychopharmacological investiga- tions – a review.Psychopharmacology (Berl),71, 173–179.
Pedlar, C., Whyte, G., Emegbo, S., Stanley, N., Hindmarch, I., &
Godfrey, R. (2005). Acute sleep responses in a normobaric hypoxic tent. Medicine and Science in Sports and Exercise, 37, 1075–1079.
Polak, A.A., van Linge, B., Rutten, F.L., & Stijnen, T. (1993).
Effect of intravenous fluid administration on recovery after running a marathon.British Journal of Sports Medicine,27, 205–
208.
Pontifex, K.J., Wallman, K.E., Dawson, B.T., & Goodman, C.
(2010). Effects of caffeine on repeated sprint ability, reactive agility time, sleep and next day performance.Journal of Sports Medicine and Physical Fitness,50, 455–464.
Rechtschaffen, A., & Kales, A. (1968).A manual of standardized terminology, techniques and scoring system for sleep stages of human subjects. Washington, DC: USA Government Printing Office.
Sleep in athletes and the effects of Ramadan S83
Downloaded by [University of Delaware] at 05:18 05 October 2014
Reilly, T., Atkinson, G., & Budgett, R. (2001). Effect of low-dose temazepam on physiological variables and performance tests following a westerly flight across five time zones.International Journal of Sports Medicine,22, 166–174.
Reilly, T., & Edwards, B. (2007). Altered sleep-wake cycles and physical performance in athletes. Physiology & Behavior, 90, 274–284.
Reilly, T., & Waterhouse, J. (2007). Altered sleep-wake cycles and food intake: The Ramadan model.Physiology & Behavior,90, 219–228.
Richmond, L., Dawson, B., Hillman, D.R., & Eastwood, P.R.
(2004). The effect of interstate travel on sleep patterns of elite Australian Rules footballers.Journal of Science and Medicine in Sport,7, 186–196.
Richmond, L.K., Dawson, B., Stewart, G., Cormack, S., Hillman, D.R., & Eastwood, P.R. (2007). The effect of interstate travel on the sleep patterns and performance of elite Australian Rules footballers. Journal of Science and Medicine in Sport, 10, 252–
258.
Roehrs, T., Hyde, M., Blaisdell, M.S., Greenwald, M., & Roth, T.
(2006). Sleep loss and REM sleep loss are hyperalgesic.Sleep, 29, 145–151.
Roky, R., Chapotot, F., Benchekroun, T.M., Benaji, B., Hakkou, F., Elkhalifi, H., Buguet, A. (2003). Daytime sleepiness during Ramadan intermittent fasting: Polysomnographic and quan- titative waking EEG study. Journal of Sleep Research, 12, 95–
101.
Roky, R., Chapotot, F., Hakkou, F., Benchekroun, M.T., &
Buguet, A. (2001). Sleep during Ramadan intermittent fasting.
Journal of Sleep Research,10, 319–327.
Roky, R., Herrera, C.P., Farooq, A., & Gaoua, N. (2011). Sleep and Chronobiology in Football Players during Ramadan. Paper presented at the 1st International Consensus Meeting on Ramadan and Football, Aspetar-Qatar Orthopaedic and Sports Medicine Hospital.
Roky, R., Houti, I., Moussamih, S., Qotbi, S., & Aadil, N. (2004).
Physiological and chronobiological changes during Ramadan intermittent fasting. Annals of Nutrition and Metabolism, 48, 296–303.
Roky, R., Iraki, L., HajKhlifa, R., Lakhdar Ghazal, N., & Hakkou, F. (2000). Daytime alertness, mood, psychomotor perfor- mances, and oral temperature during Ramadan intermittent fasting.Annals of Nutrition and Metabolism,44, 101–117.
Samuels, C. (2008). Sleep, recovery, and performance: The new frontier in high-performance athletics. Neurologic Clinics, 26, 169–180.
Silva, A., Queiroz, S.S., Winckler, C., Vital, R., Sousa, R.A., Fagundes, V., et al. (2012). Sleep quality evaluation, chron- otype, sleepiness and anxiety of Paralympic Brazilian athletes:
Beijing 2008 Paralympic Games. British Journal of Sports Medicine,46, 150–154.
Straub, W.F., Spino, M.P., Alattar, M.M., Pfleger, B., Downes, J.W., Belizaire, M.A., et al. (2001). The effect of chiropractic care on jet lag of Finnish junior elite athletes. Journal of Manipulative Physiology Therapeutics,24, 191–198.
Tafti, M., Besset, A., & Billiard, M. (1992). Effects of zopiclone on subjective evaluation of sleep and daytime alertness and on psychomotor and physical performance tests in athletes.Progress in Neuro-psychopharmacology and Biological Psychiatry, 16, 55–
63.
Taoudi, B., Roky, R., Toufiq, J., Benaji, B., & Hakkou, F. (1999).
Epidemiological study: Chronotype and daytime sleepiness before and during Ramadan.Therapie,54, 567–572.
Taylor, S.R., Rogers, G.G., & Driver, H.S. (1997). Effects of training volume on sleep, psychological, and selected physio- logical profiles of elite female swimmers.Medicine and Science in Sports and Exercise,29, 688–693.
Van Dongen H.P., Maislin G., Mullington J.M., Dinges, D.F.
(2003). The cumulative cost of additional wakefulness: Dose- response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation.Sleep,26, 117–26.
Van Dongen, H.P., Vitellaro, K.M., & Dinges, D.F. (2005).
Individual differences in adult human sleep and wakefulness.
Sleep,28, 479–496.
Vassalli, A., Dijk, D.J. (2009). Sleep function: Current questions and new approaches.European Journal of Neuroscience,29,1830–
1841.
Wall, S.P., Mattacola, C.G., Swanik, C.B., & Levenstein, S.
(2003). Sleep efficiency and overreaching in swimmers.Journal of Sport Rehabilitation,12, 1–12.
Zerguini, Y., Dvorak, J., Maughan, R.J., Leiper, J.B., Bartagi, Z., Kirkendall, D.T., et al. (2008). Influence of Ramadan fasting on physiological and performance variables in football players:
Summary of the F-MARC 2006 Ramadan fasting study.Journal of Sports Sciences,26(Suppl. 3), S3–6.
