WHY SLEEP?

Sleep is necessary for life and plays a critical role in brain function and systemic physiology, including metabolism, appetite regulation, and the functioning of immune, hormonal, and cardiovascular systems.48,49 Normal healthy sleep is characterized by duration lasting 7 to 9 hours for most adults with good quality, appropriate timing and regularity, and the absence of sleep disturbances and disorders.50 Additionally, less than 7 hours of sleep per night is associated with adverse health outcomes, including weight gain and obesity, diabetes, hypertension, heart disease and stroke, depression, and increased risk of death.50,52 Sleep disorders are categorized into 3 subjects: failure to obtain the necessary amount or quality of sleep (sleep deprivation), an inability to maintain sleep continuity (disrupted sleep, also called sleep fragmentation, difficulty maintaining sleep, and middle insomnia), and events that occur during sleep (eg, sleep apnea, restless legs syndrome).49 This article will explore sleep deprivation and sleep continuity, with specific analysis related to athletes and exercise performance.

For a bulleted summary of recommendations by Dr. Bross according to his review of the research, please see the final section titled Ways to Optimize Sleep Quantity and Quality.

THE ATHLETE’S RELATIONSHIP TO SLEEP

Athletes may require more sleep than the average human for adequate physiological and psychological recovery.5,54 Exercise and sleep appear to have cyclic effects on one another, with exercise promoting sleep efficiency and duration regardless of the intensity or mode of activity.53 However, many athletes experience inadequate sleep.2,35 Compared with non-athletes, athletes tend to sleep less (6.5–6.7 h per night) and the quality of their sleep is lower.4,5,6,7,8 Barriers to quality and quantity of sleep prior to performance includes demanding training schedules, available practice times, lengthy travel to competitions, jet lag, and pre-competition anxiety.5,8,9

FACTORS AFFECTING SLEEP

NEGATIVELY AFFECTING SLEEP

Lifestyle, sleep environment and pre-sleep behaviors can greatly affect the quality and quantity of sleep achieved in athletes. The circadian rhythm in cooperation with melatonin directs signals in the body for both drowsiness and wakefulness. Disruption of the circadian rhythm negatively impacts sleep duration and efficiency as well as athletic performance.68,69 Sleep environments that are too warm or too light can disrupt sleep,58,59 with optimal sleep environments being cool, quiet, and dark. Similarly, exposure to bright light in the late evening and use of LED screen devices can impact melatonin release and increase sleep latency, making it more difficult to fall asleep.65,66 Higher altitudes negatively impact sleep quality and duration due to reduced oxygen availability with effects seen at altitudes as low as 1,630 m (5,347 ft).75,76 Also, diets higher in fat intake are associated with sleep disorders 33 and shorter sleep duration 82 and low-carbohydrate diets are associated with decreased REM sleep.34 Likewise, higher saturated fat and lower fiber intakes may produce less slow-wave sleep, increase nighttime arousals, and a reduce overall sleep quality.35 The timing of meals also affects sleep, and eating within 30-60 minutes of sleeping has been shown to decrease sleep quality.36 Mental health is another important factor for quality and quantity of sleep with likely cyclical effects, including anxiety which has a negative impact on sleep in athletes 1 and depression, which worsens sleep quality and shortens sleep duration.84,85

SUBSTANCES AND SLEEP

Both alcohol and cannabis have detrimental effects on sleep quality when used habitually for chronic periods and in excess with effects worsening in withdrawal states but improving after periods of abstinence.47 Caffeinated beverages correlate with poor quality sleep, including increased sleep latency and decreased quality of non-REM sleep.64 Caffeine is quickly absorbed in the GI tract with 99% absorption after approximately 45 minutes,63 and often has a long half-life, between 2.5 and 4.5 hours in humans.60 Caffeine content of various food items ranges from 40 to 180 mg/150 ml for coffee to 24 to 50 mg/150 ml for tea, 15 to 29 mg/180 ml for cola, 2 to 7 mg/150 ml for cocoa, and 1 to 36 mg/28 g for chocolate.61,62

POSITIVELY AFFECTING SLEEP

Measures can be taken to positively affect the quality and duration of sleep. Maintaining a regular sleep-wake cycle helps to optimize the biological process of sleep, and a 30-60 minute period with decreased mental stimulation prior to lying down is beneficial.67 Additionally, the most effective way to optimize the circadian rhythm is with a consistent wake time.67 However, exercise has been shown to effectively modulate the circadian rhythm, inhibiting this “wind-down” period for 2-4 hours post-activity; thus, early to late afternoon has been shown to be the optimal time for exercise.70 Hydration status is linked to exercise and performance, and increased daily water intake is shown to benefit sleep.83 Aside from melatonin, supplements have not been shown to have much of an effect on sleep, but Vitamin D status positively correlates to improved sleep quality and efficiency 37,83 and increased Vitamin C intake is related to better quality sleep.83 The Mediterranean diet has been shown to be beneficial for sleep, with intake of fruits and vegetables correlating with improved sleep duration,78 higher sleep quality,80 fewer sleep changes 80 and fewer sleep disorders.79,81 This also correlates to findings suggesting diets low in saturated fat and cholesterol obtain more restorative sleep and less daytime sleepiness.83 Likewise, various fruits, including kiwi-fruit and tart cherries, have been shown to increase sleep quality and demonstrated increases in melatonin,38,39,40 with tart cherries also reducing inflammation following bouts of endurance exercise.41,42 Finally, mind-body practices, including yoga and tai-chi, have been shown to positively impact sleep quality.45,46

RELATIONSHIP OF SLEEP AND PERFORMANCE

The majority of components of sports performance, e.g. flexibility, muscle strength, short-term high power output, etc. vary with time of day in a sinusoidal manner and peak in the early evening close to the daily maximum in body temperature.10 Thus, sports performance is affected by time of day, but the optimal time can be altered, with the greatest adaptations to training occurring when exercise is performed at routine times.11,51 Of note, is the relationship between time of sleep onset and waking with weight and activity status. Late bedtimes with late wake-up times are associated with less moderate-to-vigorous physical activity and higher BMIs, independent of sleep duration.86 The effects of sleep deprivation during performance are extensive and heavily concentrated on cognitive functioning with effects ranging from increased response time to visual hallucinations.71 It has been shown that increasing sleep time and quality prior to race-day can improve performance, but runners napping during an ultramarathon tend to require more time to complete the distance.27,72 Additionally, the combination of sleep deprivation and exercise makes athletes more vulnerable to negative mood disturbances and decreased cognitive performance only during periods of rest; however, during exercise cognitive functioning is maintained.73

SLEEP DEPRIVATION AND POOR SLEEP QUALITY

Individuals poorly assess their own level of sleep impairment and greater sleep loss worsens these deficits.16 Sleep deprivation produces cognitive impairments similar to that of alcohol intoxication, with 28 hours of wakefulness equating to 0.10% BAC.17 Specifically, sleep deprivation effects cognitive functioning with greatest effect on alertness and attention, and a lesser effect on working memory.18 From a physiological standpoint, perceived exertion and neuromuscular fatigue are increased by sleep deprivation,19 with minimal effect on cardiorespiratory centers, only decreasing minute ventilation.23 Previous studies show that isolated mental fatigue does not physiologically reduce maximal muscle exertion,20 but exercise performance has both cognitive and physical inputs. In this way, it makes sense that sleep deprivation negatively impacts both speed and endurance, and has been shown to produce reductions in muscle glycogen due to poor recovery, all of which contribute to lower performance.21,22 Power activities seem less affected by sleep deprivation than endurance sports,24,25 which may be due to the increased psychobiological effect on endurance activities.57 Additionally, poor sleep can acutely affect an athlete’s health. Insomnia is correlated with psychiatric illness, including depression and anxiety, among others, and treatment-refractory psychiatric cases are associated with decreased sleep.84 Sleep deprived athletes are at increased risk for injury 29 likely due to deficits in cognitive functioning, and are more susceptible to infection in sleep deprived states, with those getting >7 hours of sleep proving to be most resilient.30,31 Finally, sleep impacts the body’s ability to manage pain, which is often cited among endurance athletes as a necessary ability for high performance in such sports. Individuals were shown to have a lower pain tolerance in states of sleep deprivation.32

COUNTERMEASURES FOR SLEEP DEPRIVATION

When optimal sleep cannot be obtained and athletes are competing in sleep-deprived states, countermeasures can be used to reduce the impact of poor sleep on performance. Napping has been shown to improve performance for sleep deprived athletes in skill-based sports by improving cognitive functioning,26 but did not show a similar positive effect on overall ultra-distance performance.27 It should be noted that performance measures for napping during activity have received little attention in endurance sports, without conclusion for pre- versus post-nap performance, focusing on the total performance outcome. Naps have otherwise been shown to be most beneficial when lasting 10 minutes, improving sleep latency, subjective sleepiness, fatigue, vigor, and cognitive performance. Napping shows decreasing positive effects when lasting 20 minutes and even negative effects when lasting 35 minutes,74 likely due to sleep inertia. Also, caffeine has been shown to reduce the impact of sleep deprivation on cognitive functioning 28 and may improve athletic performance in such states. Furthermore, the combination of a nap and caffeine may maintain high level cognitive performance even during states of severe sleep deprivation.63 Finally, exercise is positively correlated with melatonin concentration,14,15 and may be helpful in alleviating jet lag symptoms of travelers 12 and in preserving muscle glycogen stores during exercise.13

SLEEP MEDICATIONS

There has been a steady rise in the percentage of hypnotic medications being prescribed for sleep,43 even with risk of tolerance and dependence and an increased risk for Alzheimer’s disease with benzodiazepine use.44 Sleep medications should only be used for short term therapy of less than 6 weeks, if at all, while the causation for any sleep disorder is determined.

SLEEP TRACKING DEVICES

Athletes should seek to optimize their sleep duration and quality. A variety of devices can be used to measure sleep duration and efficiency including Basis Health Tracker, Misfit Shine, Fitbit Flex, Withings Pulse O2, and Actiwatch Spectrum. These devices demonstrate high accuracy for measuring sleep duration but only the Actiwath Spectrum shows accurate sleep efficiency measures.55 Additionally, the Sleep Cycle App has not demonstrated accurate measures of sleep quality.56 A few of these apps or devices use “Smart Alarms” to wake the user during periods of light sleep. These devices tend to underestimate light sleep, the targeted waking period, but may offer some benefit to prevent sleep inertia or “grogginess”.55

WAYS TO OPTIMIZE SLEEP QUALITY AND QUANTITY

The following measures are recommended to optimize sleep in athletes:

  1. Obtain adequate total sleep duration
    1. Strategy from Simpson, et al.77
      1. Track sleep for x2 weeks using a sleep diary or wrist actinigraphy
      2. Gradually increase sleep duration by 15 min every few nights
      3. Consider increasing sleep by 30-60 min/night, especially is total sleep duration is less than 7 h/night
    2. Increase nighttime sleep with progressively earlier bedtimes and consistent, early awakening
    3. Incorporate naps when nighttime sleep is constrained
      1. Revitalizing naps should last between 10 and 20 minutes
      2. Longer naps may be beneficial, but require adequate time to return to full alertness
  2. Optimize sleep environments
    1. Sleeping quarters should be cool, quiet and dark
    2. Remove devices and screens from the bedroom
    3. Initiate a 30-60 minute period of decreased stimulation in sleeping quarters prior to sleep onset
  3. Promote a healthy mental and emotional mindset
    1. Perform mind-body activities regularly
    2. Consider meditation as a form of stress relief
  4. Promote a healthy circadian rhythm
    1. Decrease caffeine intake
      1. No afternoon caffeine
    2. Decrease LED screen time
    3. Perform exercise at minimum 3-5 hours prior to sleep
    4. Set a consistent wake-time, maintain even on weekends
    5. Use melatonin supplementation in instances of travel across more than 3 time zones
  5. Eat a sleep-promoting diet
    1. Intake of high vegetables and fiber
    2. Intake of low saturated fat
      1. Intake of EPA and DHA omega-3 fatty acids
    3. Prevent eating within 30-60 minutes of sleep
      1. Limit eating to a 10-12-hour interval each day
    4. Maintain adequate hydration
    5. Maintain adequate vitamin D levels, consider supplementation especially during winter months
  6. Limit intake of substances
    1. Limit alcohol intake to ~7 standard drinks or less per week consumed over 3 or more days
    2. Limit or eliminate cannabis use

The following measures are recommended to counteract sleep deprivation in athletes:

  1. Prevent glycogen depletion
    1. Maintain carbohydrate intake during activity
      1. Higher than normal intake of simple and complex carbohydrates may be beneficial
  2. Prevent cognitive decline
    1. Increase frequency of positive reinforcement from outside sources
    2. Consume caffeine in adequate amounts
    3. Consider naps of 10 minutes in duration during “skill-based” activity in which cognitive functioning is crucial to performance
      1. For less cognitive demanding sports, consider naps of 10 minutes in duration as a last resort to help with cognitive functioning and emotional liability
  3. Adjust performance objectively
    1. Rely on external measures of performance over internal measures of effort and fatigue
      1. Wearable technology, support persons and coaching

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Teddy Bross, MD is a runner with Team RunRun who recently completed the 2018 Run Rabbit Run 100mi and is a Family Medicine Resident living in Boulder, CO.