Hit the sack. Hit the hay. Snooze. Catch some zzzs. Pass out cold. Yes, I’m referring to sleep. It's one of the most important biological states of human and animal existence, yet it’s simply one of those things we all take for granted. Sleep is paramount to both mental and physical performance. Whether you want to get stronger, bigger, or have better body composition, you must get sleep.

Sleep is a fascinating and complex topic that has so much individual variability yet has tremendous impact on life, stress, and physiological and psychological outcomes. If you don’t have insomnia and have been managing 6–8 hours per night, you’re probably thinking that you've been doing good, right? Well, there’s much more to the story. For most of us, we approach and discuss sleep as if it’s only a single layer of something. But what is sleep really? Let’s discuss and dive deeper into sleep, science, and swoleness.

But first, here are some interesting facts:

  • Nathaniel Kleitman (born in 1895 in Bessarabia—now Moldova) is known as the “father of modern sleep” and earned a doctorate from the University of Chicago.
  • One of his graduate students (Eugene Aserinsky) stumbled on to a great discovery for his dissertation topic. Kleitman’s daughter (Ester) and Aserinsky in 1953 introduced the world to “rapid eye movement,” or REM sleep, making sleep a truly scientific field.
  • Prior to the invention of the incandescent light bulb, we reportedly got about twelve hours of nightly sleep on average. Before alarm clocks were invented, there were “knocker-ups” who went tapping on client’s windows with long sticks until they were awake.
  • Dogs and cats sleep over 70 percent of their lives.
  • Man and woman are the only mammals that willingly delay sleep.

Sleep 101

What is sleep? Well for starters, sleep can be defined as a reversible behavioral state in which an individual is perceptually disengaged from and unresponsive to the environment (11). It is within the ‘suprachiasmatic nucleus’ (SCN) of the hypothalamus (the brain site of our circadian clock) that the circadian rhythm, including the sleep-wakefulness cycle, is regulated.

Sleep has two primary (and complex) physiological and behavioral states. We know these as rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. NREM sleep is divided into four stages (five if you count REM) that are linked with a progressive increase in the depth of sleep (11). Here’s another fact—the release of certain neurotransmitters (norepinephrine, serotonin, and histamine) is completely shut down during REM, which produces muscle atonia (a paralysis type of sensation during sleep), bursts of REM, and dreaming. Therefore, REM sleep is considered to be a condition with an activated brain in a paralyzed body. Very cool, isn’t it?Woman lies with sleeping mask in the bed

During the night, sleep patterns repeat intermittently, moving sequentially through four stages of non-REM sleep into REM sleep, which constitutes about 25 percent of total sleep and initially lasts approximately ten minutes and extends with each repeating cycle, lasting up to an hour in the last phase. During REM sleep, the eyes move back and forth rapidly and the body’s muscular contraction activity is minimal. There are several stages of sleep, which has led to a whole taxonomy of sleep. It’s important to mention that beta waves are the earliest stages of sleep because you're still awake and alert while you lay in bed watching episodes of Breaking Bad.

In Stage 1 (as we prepare to drift off), the brain emits alpha and theta waves. This is actually where “daydreaming” comes in, except we fall asleep. These alpha and theta waves are slower and more regular compared to the waves emitted by the part of our brain that’s awake. Individuals who practice meditation typically “hang out” in stage 1. In this stage, it’s very common to experience strange and extremely vivid sensations. One of the best examples is the feeling of falling or somebody calling your name followed by sudden muscle contractions. These are known as hypnagogic hallucinations, a collective term for sights, sounds, and other sensations experienced during the transition between wakefulness and sleep (31). Briefly following, we enter theta, which is still a relatively light period between being awake and asleep and lasts a very short period of five to ten minutes.

Stage 2 lasts approximately twenty minutes, as our brain begins to generate very short periods of rapid, rhythmic brain wave activity known as sleep spindles (3). Sleep spindles are a hallmark of non-rapid eye movement (NREM). At this point, body temperature and heart rate are reduced.

Stage 3 is where things start to pick up as delta waves start to emerge, which are very slow and have much larger amplitudes. Stage 3 is often referred to as delta sleep or “slow wave sleep.” Stage 3 and 4 are typically combined stages. In stage 3, it is often difficult to awaken a person, and if awakened, the person will feel disoriented for several minutes (yes, this happens to everyone). Blood flow is directed away from the brain to other parts of the body for restorative purposes. A person can be woken in stage 1 sleep by a slight noise (yes, the “light sleepers”). By stage 3, he/she might sleep through a very loud bang (perhaps somebody eagerly trying to steal your protein powder). In any case, it isn't good. Considering that sleep is vital to recovery, it is within this specific sleep stage (slow wave sleep) that growth hormone is released within humans. This has been well documented (18, 27, 33, 41, 43, 46) and suggests that optimum conditions for anabolism (swoleness) prevail during sleep and that the duration of slow wave sleep are proportional to preceding wakefulness (39). In addition, if/when sleep deprivation is apparent, slow wave sleep is decreased, facilitating an increase in daytime sleepiness and a reduction in performance (14).

Stage 4 delta sleep lasts about 25 to thirty minutes. Sleepwalking and/or bed wetting (hopefully that isn't you) occur in this stage of sleep.

Children in Balloon

Stage 5, the final stage of sleep, is where we dream. It is actual REM sleep, lasting about ninety to 120 minutes of a night's sleep, and is accompanied by increased respiration rate and brain activity. Herein lies a huge problem for so many individuals. If you repeatedly wake up before you get into REM sleep, you’ll begin to suffer detrimental effects to memory, motor skills, and general performance.

Dreaming occurs because of increased brain activity, but voluntary muscles become paralyzed. Although they can vary substantially, the length of a dream may last for a few seconds or as long as twenty to thirty minutes (19). Interestingly, the average person has three to five dreams per night, but some may have up to seven dreams in one night (19). These dreams can be combinations of emotion, visuals, sexual themes, black and white versus color (38), nightmares, déjà vu, or any other phenomenon. The paralyzing effect during dreams is actually a built-in protective mechanism to keep you from hurting yourself. Have you ever felt like you can’t escape during a dream? Well, it turns out you can’t. You can breathe and your basic physiology is functioning, but you really can’t move.


Screen Shot 2014-05-19 at 9.54.16 AM

Sleep, recovery, and training

Most of us hard training athletes need about seven to 8.5 hours of sleep each day (2), of which 80–90 percent should be during the night. Sleep also serves as a restorative process for energy resources, tissue recovery, thermoregulation, and cognitive function (1), and deep sleep is vital for maximizing physiological growth and repair (20). Sleep is recognized as an essential component of recovery from performance training and anecdotally reported to be the single most efficacious recovery strategy. Adequate sleep is also vital for athletes who are injured or traveling or are in heavy periods of training or competition phases (36, 37). Poor sleep quality, predominantly during high training loads and competition periods, has been identified as a marker of underrecovery and a contributing factor of overreaching and overtraining (13).

We all have experienced sleep disturbances the night prior to a competition, which is all too common for hard training athletes. Recent research investigated the precompetitive sleep behavior of 103 athletes and how it relates to precompetitive mood and subsequent performance. (25). Results revealed that on the night before competition, athletes slept well under the recommended target of eight hours of sleep for healthy adults, with almost 70 percent of athletes experiencing poorer sleep than usual. It was found that anxiety, noise, the need to use the bathroom, and early event times were among the most commonly reported causes of disrupted sleep in athletes on the night prior to competition. Of course, disrupted sleep on the night prior to competition can negatively relate to an athlete’s precompetitive mood states. Although not conveyed in the literature, anecdotal evidence also suggests that athletes who compete at night also have complications falling asleep post-competition.

It’s been shown that hard training athletes have sleep disturbances in part related to higher nighttime epinephrine (adrenaline) and norepinephrine concentrations (30). Similarly, a doubling of training load has been reported to provoke insomnia and depression as part of the overtraining syndrome (45).

Enter the deprivation

Sleep deprivation, sleep loss—it’s all the same. When we don’t sleep, the circadian rhythm gets off-track, hormones get crazy, and we can’t recovery as effectively. Loss of sleep certainly impacts a wide variety of physiological outcomes such as altered glucose control, abnormal cortisol, and of course, overall hormonal imbalances such as lower testosterone in men (no swoleness), which impedes training recovery due to decreased protein synthesis. There are a whole host of consequences of sleep deprivation beyond just reductions in exercise performance, both in the general populations and in athletes.

Let’s examine a variety of consequences of sleep deprivation. This, of course, isn't an exhaustive list but highlights major components involved in sleep loss.

sleep athletic performance dependent on sleep jon mike 052914

Strength and power

Blumert and colleagues (4) examined the effects of 24 hours of sleep deprivation in nine US college-level weightlifters in a randomized counterbalanced design. There weren't any differences in any of the performance tasks (snatch, clean and jerk, front squat, and total volume load and training intensity) following 24 hours of sleep deprivation when compared with no sleep deprivation (4). However, mood state, as assessed by the profile of mood states (a questionnaire used for overtraining), was significantly altered with confusion, vigor, fatigue, and total mood disturbance all negatively impacted by sleep deprivation. There have also been performance declines in isokinetic knee extension and flexion torque after thirty hours of sleep deprivation in trained men (9). An early study also found a significant effect of sleep loss on maximal bench press, leg press, and deadlifts but not maximal bicep curls. Submaximal performance was significantly negatively affected on all four tasks and to a greater extent compared to the maximal efforts (34).

Bottom line on strength and power: In all likelihood, sleep loss will affect your gains, but individual variability does exist as well as differences in training responses and programs.


Testosterone is also affected by your total amount of sleep. This makes sense, as our bodies make much more testosterone when we're asleep than when we’re awake. A lack of sleep can most certainly create a decrease in testosterone. A recent investigation found that men who slept less than five hours a night for one week in a laboratory had significantly lower levels of testosterone (by over 10 percent) than when they had a full night’s sleep (26) whereas an early report showed a 30.4 percent decrease (12). Interestingly, these reductions all happened within 24 hours of sleep deprivation (13, 17).

In a study by Leproult and colleagues (26), the participants spent three nights in the laboratory sleeping for up to ten hours and then eight consecutive nights sleeping less than five hours. Their blood was sampled every 15 to thirty minutes for 24 hours during the last day of the ten-hour sleep phase and the last day of the five-hour sleep phase. The results showed that sleep loss on testosterone levels were apparent after just one week of decreased sleep, and five hours of sleep decreased their testosterone levels by ten to fifteen percent. It was also found the men had the lowest testosterone levels in the afternoons on their sleep restricted days, between 2:00 p.m. and 10:00 p.m., and also self-reported their mood and vigor levels throughout the study. In addition, the young men reported a decline in their sense of well being as their blood testosterone levels reduced. Their mood and vigor actually decreased more per day as the sleep restriction part of the study continued.

lifter sleep squat jon mike 052914

Growth hormones are secreted in a pulsatile fashion from the anterior pituitary shortly after sleep. As previously mentioned, growth hormone is well documented for promoting anabolic effects during sleep. However, considerable sleep deprivation for multiple nights can undoubtedly crush growth hormone. But some evidence indicates that neither an irregular sleep cycle [i.e. night shift workers (7)] nor only sleeping for four hours a night (41) will adversely affect whole-day exposure to growth hormone. Although sleep loss can disturb changes in the growth hormone cycle, overall exposure is still present, as the body appears to compensate during normal waking hours.

Cortisol is a steroid hormone that is produced in the adrenal cortex located on top of each kidney. Cortisol is released in a highly irregular manner with peak secretion in the early morning, which then tapers out in the late afternoon and evening. Fasting, food intake, exercising, awakening, and psychosocial stressors cause the body to release cortisol, but it has a slightly different response when sleep loss is apparent. The majority of the recent science on cortisol and sleep deprivation shows either no change or slight increases. Some studies even normalize this difference and increase overall exposure to cortisol over a full day.

Similar to cortisol, insulin doesn’t appear to be highly disastrous to sleep loss (unless you eat a large meat-lovers pizza with everything drizzled in olive oil right before your four hours of sleep...then it might be an issue). However, some evidence does show a decrease in insulin sensitivity in the fat cells and liver (8, 15). Some evidence reports that this decrease in insulin sensitivity can be attributed to getting half your normal amount of sleep for less than a week (10, 35).

Bottom line with sleep and hormones: Try not to screw them up! For those of you who are ramping up training efforts for competition, you may want to get more total hours on the pillow.


Studies support the notion that chronic partial sleep loss can increase the risk of obesity and diabetes (24). This includes changes in glucose regulation via insulin resistance, deregulation of neuroendocrine control of appetite, and/or increased energy intake (1, 40). Sleep deprivation has also been shown to have decreases in leptin and increases in ghrelin [appetite regulating hormones (47)]. Sleep loss has also been shown to increase hunger and appetite, particularly in relation to carbohydrate-rich foods (42). Metabolic rate itself is a bit mixed. One study found that getting three fewer hours of sleep per day for two weeks resulted in a 7.6 percent reduction in metabolic rate (29) whereas other reports showed no decrease (6, 32). To add to the mix, a recent study in adolescent boys reported that less sleep actually resulted in additional calories expended (23), meaning the subjects expended more (being awake longer) and consumed less (decreased appetite).

time to wake up

Bottom line with metabolism: Altered glucose metabolism and neuroendocrine function can create concern regarding carbohydrate metabolism, appetite, food intake, and protein synthesis.


There isn't any doubt that one of the most studied areas of the science of sleep deprivation is the effects on alertness and performance (44). It is estimated that the consequences cost billions of dollars worldwide per year due to accidents, direct healthcare costs, and reduced efficiency and productivity (44). Sleep loss surely decreases the effects of learning and memory and is critical for learning and preparing the brain for next-day memory development (48). Interestingly, a recent study found that 24 hours of sleep deprivation significantly heightened the levels of stress hormones and lowered attention and working memory, meaning that the acute loss in sleep rendered the subjects more susceptible to making errors despite the fact that they were all good sleepers, had no history of medical or neuropsychiatric diseases, weren't taking any kind of medication, and were in their early to mid 20s (22). Although a lack of overall evidence exists on the effects of sleep deprivation risk of acute injury (i.e. decreased focus, poor execution, or lowered reaction times), it’s likely that sleep deprivation may increase susceptibility to injury.

Bottom line on cognition: Sleep loss can negatively impact learning and memory and likely increase the risk of injury and work related errors.

Immune response and inflammation

Ever have the feeling of sickness and headaches due to loss of sleep? Say I! Well, a recent review examined the link between sleep and immune response and concluded that sleep improves immune responses and that most immune cells have their peak pro-inflammatory activity at night (5). This means that sleep loss will certainly impair immune responses, increasing risk of illness. A recent study examined immune function response in subjects who naturally slept for less than seven hours, seven to nine hours, or longer than nine hours (16). Short sleep duration was associated with 49 percent higher T-cell function in response to an antigen and 30 percent lower natural killer cell activity when compared with normal sleep. Simply, sleep loss lowers immune function.

Human digestive system - back view

Inflammatory markers are also present with sleep deprivation. Interleukins (naturally occurring proteins produced by the body that have infection-fighting immune responses), tumor necrosis factor-α (important mediator of the body’s response to infection), and C-reactive protein (a substance produced by the liver that increases in the presence of inflammation in the body) are all influenced by a lack of sleep (28) as well as gender differences (21). Those people with insomnia and sleep apnea have elevated inflammatory markers (28), which absolutely affects insulin sensitivity, metabolism, blood pressure, and sleep.

Bottom line on immune response and inflammation: Loss of sleep does decrease immune function and can adversely affect performance while additional and consistent sleep surely helps reverse the process.

Stay tuned for part two of "Sleep, Science, and Swoleness"!


  1. Aldabal L, Bahammam AS (2011) Metabolic, endocrine, and immune consequences of sleep deprivation. The Open Respiratory Medicine Journal 5:31–43.
  2. Alhola P, Polo-Kantola P (2007) Sleep deprivation: Impact on cognitive performance. Neuropsychiatric Disease and Treatment 3:553–67.
  3. Andrillon T, Nir Y, Staba RJ, Ferrarelli F, Cirelli C, Tononi G, Fried I (2011) Sleep spindles in humans: insights from intracranial EEG and unit recordings. J Neurosci 31:17821–834.
  4. Blumert PA, Crum AJ, Ernsting M, Volek JS, Hollander DB, Haff EE, Haff GG (2007) The acute effects of twenty-four hours of sleep loss on the performance of national-caliber male collegiate weightlifters. J Strength Cond Res 21:1146–54.
  5. Bollinger T, Bollinger A, Oster H, Solbach W (2010) Sleep, immunity, and circadian clocks: a mechanistic model. Gerontology 56:574–80.
  6. Bosy-Westphal A, Hinrichs S, Jauch-Chara K, Hitze B, Later W, Wilms B, Settler U, Peters A, Kiosz D, Muller MJ (2008). Influence of partial sleep deprivation on energy balance and insulin sensitivity in healthy women. Obesity Facts 1:266–73.
  7. Brandenberger G, Weibel L (2004) The 24-h growth hormone rhythm in men: sleep and circadian influences questioned. Journal of Sleep Research 13:251–55.
  8. Broussard JL, Ehrmann DA, Van Cauter E, Tasali E, Brady MJ (2012) Impaired insulin signaling in human adipocytes after experimental sleep restriction: a randomized, crossover study. Ann Intern Med 157:549–57.
  9. Bulbulian R, Heaney JH, Leake CN, Sucec AA, Sjoholm NT (1996) The effect of sleep deprivation and exercise load on isokinetic leg strength and endurance. Eur J Appl Physiol Occup Physiol 73:273–77.
  10. Buxton OM, Pavlova M, Reid EW, Wang W, Simonson DC, Adler GK (2010). Sleep restriction for 1 week reduces insulin sensitivity in healthy men. Diabetes 59: 2126–133.
  11. Carskadon MA DW. Normal human sleep: An overview. In: Kryger MH, Roth T, Dement WC, editors (2011) Principles and practice of sleep medicine. 5th ed. St. Louis: Elsevier, 16–26.
  12. Cortes-Gallegos V (1983) Sleep deprivation reduces circulating androgens in healthy men. Arch Androl.
  13. Cote KA, McCormick CM, Geniole SN, Renn RP, MacAulay SD (2013) Sleep deprivation lowers reactive aggression and testosterone in men. Biol Psychol 92:249–56.
  14. Dijk DJ (2010) Slow-wave sleep deficiency and enhancement: implications for insomnia and its management. The World Journal of Biological Psychiatry: The Official Journal of the World Federation of Societies of Biological Psychiatry 11(S1):22–28.
  15. Donga E, van Dijk M, van Dijk JG, Biermasz NR, Lammers GJ, van Kralingen KW, Corssmit EP, Romijn JA (2010) A single night of partial sleep deprivation induces insulin resistance in multiple metabolic pathways in healthy subjects. J Clin Endocrinol Metab 95:2963–68.
  16. Fondell E, Axelsson J, Franck K, Ploner A, Lekander M, Balter K, Gaines H (2011) Short natural sleep is associated with higher T cell and lower NK cell activities. Brain, Behavior, and Immunity 25:1367–375.
  17. Gonzalez-Santos MR, Gaja-Rodriguez OV, Alonso-Uriarte R, Sojo-Aranda I, Cortes-Gallegos V (1989) Sleep deprivation and adaptive hormonal responses of healthy men. Arch Androl 22:203–07.
  18. Gronfier C, Brandenberger G (1998) Ultradian rhythms in pituitary and adrenal hormones: their relations to sleep. Sleep Medicine Reviews 2:17–29.
  19. Hobson JA (2009) REM sleep and dreaming: towards a theory of protoconsciousness. Nat Rev Neurosci 10:803–13.
  20. Hudson-Walters P (2004) Sleep: The athlete and performance. Strength Cond J 24:17–24.
  21. Irwin MR, Carrillo C, Olmstead R (2010) Sleep loss activates cellular markers of inflammation: sex differences. Brain, Behavior, and Immunity 24:54–57.
  22. Joo EY, Yoon CW, Koo DL, Kim D, Hong SB (2012) Adverse effects of 24 hours of sleep deprivation on cognition and stress hormones. Journal of Clinical Neurology 8:146–50.
  23. Klingenberg L, Chaput JP, Holmback U, Jennum P, Astrup A, Sjodin A (2012) Sleep restriction is not associated with a positive energy balance in adolescent boys. Am J Clin Nutr 96:240–48.
  24. Knutson KL, Spiegel K, Penev P, Van Cauter E (2007) The metabolic consequences of sleep deprivation. Sleep Medicine Reviews 11:163–78.
  25. Lastella M, Lovell GP, Sargent C (2014) Athletes’ precompetitive sleep behavior and its relationship with subsequent precompetitive mood and performance. Eur J Sport Sci 14(S1):S123–30.
  26. Leproult R, Van Cauter E (2011) Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA 305:2173–174.
  27. Marshall L, Molle M, Boschen G, Steiger A, Fehm HL, Born J (1996) Greater efficacy of episodic than continuous growth hormone-releasing hormone (GHRH) administration in promoting slow-wave sleep (SWS). J Clin Endocrinol Metab 81:1009–13.
  28. Mullington JM, Simpson NS, Meier-Ewert HK, Haack M (2010) Sleep loss and inflammation. Best Practice & Research Clinical Endocrinology & Metabolism 24:775–84.
  29. Nedeltcheva AV, Kilkus JM, Imperial J, Schoeller DA, Penev PD (2010). Insufficient sleep undermines dietary efforts to reduce adiposity. Ann Intern Med 153:435–41.
  30. Netzer NC, Kristo D, Steinle H, Lehmann M, Strohl KP (2001) REM sleep and catecholamine excretion: a study in elite athletes. Eur J Appl Physiol 84:521–26.
  31. Ohayon MM, Priest RG, Caulet M, Guilleminault C (1996) Hypnagogic and hypnopompic hallucinations: pathological phenomena? The British Journal of Psychiatry: The Journal of Mental Science 169:459–67.
  32. Opstad PK, Falch D, Oktedalen O, Fonnum F, Wergeland R (1984) The thyroid function in young men during prolonged exercise and the effect of energy and sleep deprivation. Clin Endocrinol (Oxf) 20:657–69.
  33. Perras B, Marshall L, Kohler G, Born J, Fehm HL (1999) Sleep and endocrine changes after intranasal administration of growth hormone-releasing hormone in young and aged humans. Psychoneuroendocrinology 24:743–57.
  34. Reilly T, Piercy M (1994) The effect of partial sleep deprivation on weight-lifting performance. Ergonomics 37:107–15.
  35. Reynolds AC, Dorrian J, Liu PY, Van Dongen HP, Wittert GA, Harmer LJ, Banks S (2012) Impact of five nights of sleep restriction on glucose metabolism, leptin and testosterone in young adult men. PLoS One 7:e41218.
  36. Samuels C (2008) Sleep, recovery, and performance: the new frontier in high-performance athletics. Neurologic Clinics 26:169–80.
  37. Samuels C (2009) Sleep, recovery, and performance: The new frontier in high-performance athletics. Phys Med Rehabil Clin N Am 20:149–59.
  38. Schredl M, Ciric P, Gotz S, Wittmann L (2004) Typical dreams: stability and gender differences. The Journal of Psychology 138:485–94.
  39. Shapiro CM, Bortz R, Mitchell D, Bartel P, Jooste P (1981) Slow-wave sleep: a recovery period after exercise. Science 214: 1253–1254.
  40. Spiegel K, Knutson K, Leproult R, Tasali E, Van Cauter E (2005) Sleep loss: a novel risk factor for insulin resistance and Type 2 diabetes. J Appl Physiol (1985) 99:2008–19.
  41. Spiegel K, Leproult R, Colecchia EF, L’Hermite-Baleriaux M, Nie Z, Copinschi G, Van Cauter E (2000). Adaptation of the 24-h growth hormone profile to a state of sleep debt. Am J Physiol Regul Integr Comp Physiol 279:R874–83.
  42. Spiegel K, Tasali E, Penev P, Van Cauter E (2004) Brief communication: Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Ann Intern Med 141:846–50.
  43. Steiger A, Guldner J, Hemmeter U, Rothe B, Wiedemann K, Holsboer F (1992) Effects of growth hormone-releasing hormone and somatostatin on sleep EEG and nocturnal hormone secretion in male controls. Neuroendocrinology 56:566–73.
  44. TJ. B (2011) Performance deficits during sleep loss: effects of time awake, time of day, and time on task.
  45. Uusitalo AL, Valkonen-Korhonen M, Helenius P, Vanninen E, Bergstrom KA, Kuikka JT (2004) Abnormal serotonin reuptake in an overtrained, insomnic and depressed team athlete. Int J Sports Med 25:150–53.
  46. Van Cauter E, Caufriez A, Kerkhofs M, Van Onderbergen A, Thorner MO, Copinschi G (1992) Sleep, awakenings, and insulin-like growth factor-I modulate the growth hormone (GH) secretory response to GH-releasing hormone. J Clin Endocrinol Metab 74:1451–59.
  47. Van Cauter E, Spiegel K, Tasali E, and Leproult R (2008) Metabolic consequences of sleep and sleep loss. Sleep Medicine 9(S1):S23–28.
  48. Walker MP (2008) Cognitive consequences of sleep and sleep loss. Sleep Medicine 9(S1):S29–34.