Get swole with 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. For most of us, we approach and discuss sleep as if it’s only a single layer of something.
So, what is sleep really? Let’s discuss and dive deeper into sleep, science, and swoleness.
A few fun facts about sleep:
- 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.
- 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.
- Human beings are the only mammals that willingly delay sleep.
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?
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. Blood flow is directed away from the brain to other parts of the body for restorative purposes. A person can be woken up in stage 1 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 (aka 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).
Delta sleep lasts about 25 to 30 minutes. Sleepwalking and/or bed wetting occur in this stage of sleep.
The final stage of sleep is where we dream. It is actual REM sleep, lasting about 90 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 phenomenona. 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.
Sleep, recovery, and training
Most of hard training athletes need about seven to eight and a half 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, traveling, 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 under-recovery 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).
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 recover 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.
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 wellbeing as their blood testosterone levels reduced. Their mood and vigor actually decreased more per day as the sleep restriction part of the study continued.
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). 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).
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. This means 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, 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 put, sleep loss lowers immune function.
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 affect 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 whereas additional and consistent sleep surely helps reverse the process.
Download the references and additional resources: references-sleep-to-swoleness-dr.-j-mike