Sports Chronobiology Consultation: From the Lab to the Arena
Section snippets
Minimizing adversity
The minimum goals of a sports chronobiology consultation are to avoid or reduce potential decrements in performance related to circadian (eg, early morning, early afternoon, or late evening dips in performance caused by jet lag), menstrual, or seasonal adversity, and to prevent or minimize the effects of less-than-optimal quantity or quality of sleep [8].
Maximizing performance
A key point of sports chronobiology is that peak performance, known as the “greatest moments,” “flow,” “individual zone of optimal
Subjective scales of sleep, sleepiness, and alertness
To assess sleepiness/alertness, a number of subjective questionnaires have been developed. The Epworth Sleepiness Scale (ESS) [12] asks for a self-report of sleepiness over time, varying from several weeks to a month, and normative data are available.
A number of scales have been used for assessing sleepiness (ie, the immediate urge to sleep), such as the Karolinska Sleepiness Scale (KSS) and Stanford Sleepiness Scale. The KSS [13] is a nine-point sleepiness scale ranging from 1 (very alert) to
Alertness-enhancing drugs
Because some professional athletes use stimulants to improve performance, sports medicine practitioners should be constantly aware of this possibility. Use of stimulants can induce major fluctuations in alertness and mood, in addition to rarely inducing a frank psychosis and bizarre behavior. By World Anti-Doping Agency (WADA) standards, stimulant use to improve performance is considered doping [17].
Athletes may take stimulant drugs to improve performance, to mask fatigue, for recreation, or
Sleep/wake considerations in athletes with mood disorders
Dysfunctional sleep is a cardinal symptom associated with depression. Although insomnia [24] is common in depression, increased sleepiness is not rare. Atypical depression is characterized by increased sleep, increased rather than decreased appetite, and weight gain rather than weight loss. Disturbances of circadian rhythms are also common in depression [24], and a variety of chronobiologic interventions have been used in the treatment of depression. Of particular importance is bright light
Homeostatic and circadian impairments in alertness and sports performance
Impairment in alertness could be the consequence of a homeostatic and circadian hardship. The homeostatic hardship relates to the appetitive function of sleep (ie, sleep being like thirst, appetite, and so forth), in that its behavior increases with its absence and decreases with its abundance. The circadian hardship relates to less-favorable time windows for performance associated with an internal promotion of the propensity to sleep under the control of the “body clock,” or the
Importance of monitoring sleep at high altitude
Hypoxia of high altitude impairs physical performance, mental performance, and sleep. Sleep impairment is often reported to be the most distressing challenge during high-altitude exposure [26].
Sleep disturbance is a frequent feature of an acute ascent at high altitude, with the most common symptoms being frequent awakening and waking up unrefreshed [27]. An increased number of awakenings, periodic breathing, and a shift from deeper to lighter sleep stages (ie, decreases in stages 3 and 4,
Sleep as a marker of fitness to perform
Sleep is an important marker of well-being, so any issue concerning the quality of sleep may signal a correctable factor affecting the athlete's performance. For instance, many underlying physical and emotional problems associated with overtraining, including fatigue, anxiety, or depression, may initially present as sleep-related complaints. Less than average ratings of sleep quality should be followed up as soon as possible with an interview by an experienced practitioner. Important points to
Circadian adversity
A biological rhythm has been defined as an alternating sequence of events, which in a steady state repeat themselves in a constant order and interval. Rhythms with a period of approximately 24 hours are called circadian. If a phenomenon shows a variation between different times of the day, but does not manifest a repeated rhythm, it is said to have diurnal variations. Many view sine waves as a prototype rhythm with maximums (peak), minimums (troughs), acrophase (timing of the peak), and mesor
Sleep gates, wake maintenance zones, and performance
Over 24 hours there are predictable distinct periods of time when it is relatively easy to fall asleep, and these periods alternate with other distinct periods when it is relatively difficult to fall asleep. The two distinct periods when it is easy to fall asleep can be viewed as sleep gates. The first of these periods is the postprandial dip, which usually occurs between 1300 and 1600 and occurs more frequently, but not exclusively, in morning individuals (Fig. 5). Monk provides a detailed
Refractory periods for falling asleep
The refractory periods for sleep occur in the late morning and late afternoon/evening. The evening refractory period is in fact paradoxical (ie, people are often more alert just before they usually go to bed than when they wake up), in that it usually occurs 3 hours before the habitual time for bed (under constant conditions) and is associated with the stimulating effect of the circadian system that compensates for the accumulated time awake and associated sleep pressure, as described by
Evidence that the wake maintenance zone is optimal for sports performance
World records are usually broken by athletes competing in the later afternoon to early evening hours, as seen in runners, weight throwers, and 100- and 200-meter swimmers (see references [1], [44]). These investigators also reviewed the methodological challenges related to laboratory studies of circadian effects on sports performance, and observed some consistent findings in diurnal variation. For instance, speed of reaction time and muscle strength peaked consistently in the early evening.
Morningness–eveningness
Some people tend to naturally wake up very early (“larks”) and others to stay up very late (“owls”). Although environmental factors pay an important role, endogenous circadian rhythms have been shown to determine the chronotype, or the “morningness–eveningness” preference. Since the original formulation of a morningness-eveningness questionnaire by Horne and Ostberg [45], other questionnaires have been proposed, such as one by Torsvall and Akerstedt [46], and the one by Smith et al [47] that we
Circadian markers
Certain physiologic markers are essential when designing interventions for shifting circadian rhythms. One of the most important circadian markers is the timing of the central temperature minimum (Tmin). For this purpose, Tmin should be measured in constant conditions during extended wakefulness using a rectal probe in a constant position at rest with regular intake of water and food. This should be monitored continuously to eliminate “masking” by the sleep/wake cycle, positional physiologic
Hormonal markers
Biological day–night alterations are characterized by predictable rhythmic changes of certain hormones. Two of the most important are melatonin and cortisol. Cortisol levels start and continue to increase during the biological night, and decrease during the biological day. Melatonin is a hormone secreted during darkness. Its secretion begins approximately 2 hours before the usual bedtime and is limited to the biological night. Because melatonin is suppressed by bright light, it should be
Jet lag
Transcontinental travel is potentially disruptive for sports performance. Chronobiology interventions are critical for shortening and minimizing these disturbances. Even crossing few time zones may result in changes in the performance levels. For example, Recht et al [48] showed that 1.24 more home runs were hit in a Major League Baseball game by the home team when playing against a visiting team that had traveled eastward.
Although it usually represents a liability, transmeridian travel may
Room light and jet lag
Lower intensities of light, similar to those present in routine illumination conditions, have been shown to suppress melatonin and shift circadian rhythms [54]. For instance, room light in a jet-lag simulation has been shown to alter circadian rhythms [55]. Thus, exposure to room light in the hotel or at practice, if extended over several hours, should be considered active from a circadian standpoint and, depending on whether it occurs during a “favorable” or “unfavorable” interval, may either
Situations in which it may be detrimental to make a circadian phase adjustment to the destination time
One situation where circadian shifts to the new time zone should be avoided is when a short trip away from home is followed by an important competition or home game scheduled a short time after the return and there is not enough time to comfortably readjust. In this case, all efforts must be made during the short trip to avoid light exposure to the eyes (eg, using window shades, having minimal lights in the room, wearing dark sunglasses that ideally block or reflect short wavelength light,
Delayed sleep phase syndrome
Delayed sleep phase syndrome (DSPS) is a clinical syndrome commonly encountered by young high school and college athletes, and observed less frequently in adults. These athletes often cannot fall asleep until late at night, but still have to wake up early in the morning for practice and academic activities. Attempting to go to bed earlier does not work in most of these cases because the wake maintenance zone has shifted (delayed to a time when they would ideally be sleeping), and therefore it
Infradian rhythms
Infradian rhythms have a period longer than 24 hours (eg, menstrual, seasonal). For the implications of menstrual rhythms on athletic performance, see the article by Constantini et al on menstrual rhythms elsewhere in this issue. For a further discussion of the relevance of seasonal rhythms for athletes, see the article on seasonality of exercise by Atkinson and Drust, the article on bright light treatment by Postolache and Oren, and the article on the effect of seasonal allergies on athletic
Summary
In addition to preventing performance deterioration and contributing to better health, implementing chronobiologic methods to preserve alertness may help certain athletes avoid or discontinue unethical and illegal use of stimulants.
The science of chronobiology relies on precise measurements in highly controlled environments. Additional studies looking at relevant outcome measures using these standards of design for performance in sports are necessary. However, the practice of chronobiology (as
Acknowledgments
We acknowledge those individuals who directly or indirectly contributed to data we present in this article. We would like to thank Ev- K2- CNR (Italy), Harold Been, MD, Arnold Winston, MD, Agostino Da Polenza, Gian-Pietro Verza, William Gruen, and Mal Duff for their help in the high altitude sleep study.
Many thanks go to Dr. Der Chia Lin, the Director of the National Training Center and the Chief of Chinese Taipei Mission at the Athens 2004 Olympic games for his far-sighted understanding of the
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Because of the growing concern regarding use of stimulants in athletes of all ages to improve alertness, reduce fatigue, and maintain aggressiveness, several paragraphs in this article address this important doping issue.
Certain interventions for optimizing sleep/wake and aligning biological rhythms with competitive demands are safe and effective in improving qualities that are essential for competitive athletes (eg, alertness, attention, concentration, mood, reaction time, psychomotor learning). These interventions need to be evaluated and specifically tailored to the individual athlete, sport, and environmental conditions.