Many of us know the satisfying experience of crashing into a deep, restful sleep after a long hike or a hard workout at the gym. But the fitness results aren’t instantaneous; we don’t immediately improve cardiovascular health, lose weight, and gain muscle mass on the trail or at the gym. These things happen after a restoring night of restful sleep.
Sleep and fitness have a tightly linked bidirectional relationship. That is to say, good quality sleep results in better exercise performance, which in turn creates better sleep in a positive, self-sustaining cycle.
To understand how vital sleep is to our fitness goals, let’s unpack the relationship a little further. While we’re at it, we’ll take a look at how much sleep athletes should get and if fitness trackers can play a meaningful role in providing effective insights into how to optimize sleep for fitness and vice versa. We’ll also take a look at how sleep deprivation, even as little as one night, can wreak havoc on our ability to recover from or even participate in a good workout.
Why is sleep so important for fitness results?
Sleep is a crucial period of body and mind restoration. High-quality sleep improves fitness by regulating cellular repair and the levels of certain hormones associated with physical performance and recovery. Sleep regulates the functioning of several important hormones important for post-workout recovery.
Human Growth Hormone (HGH): The great healer of the body
Sleep, especially deep sleep, is an important restorative time for the body. During deep non-REM sleep, our body produces high amounts of human growth hormone (HGH). HGH is an anabolic hormone that regulates cellular growth and repair and plays a crucially important role in regulating the metabolism of protein, fats, and carbohydrates. Both sleep and exercise prompt your brain to release growth hormone, but as much as 70% of its secretion occurs during slow-wave (deep) sleep.
For those of us who don’t get enough sleep, our bodies won’t produce enough growth hormone to effectively repair our muscles after a workout. Plus, our bodies struggle to repair the linings of our blood vessels.
So while in most cases regular physical activity is one of the best ways to maintain artery health, poor sleep can drastically thwart these efforts. With the integrity of our blood vessels weakened, we are more predisposed to a host of arterial and heart diseases.
Insufficient sleep can also lead to insulin resistance and impair glucose tolerance, which can disrupt the supply of energy to muscles. When we’re getting enough sleep and growth hormone levels are optimum, our bodies benefit from an increased level of circulating glucose and increased protein synthesis. These are both vitally important for the growth and maintenance of lean muscle mass.
Cortisol: The double-edged stress hormone
Like many other hormones, cortisol levels naturally wax and wane throughout a 24-hour period. Cortisol levels decrease at night, hitting the lowest level around midnight. Levels then gradually increase and peak in the early morning in order to promote wakefulness.
Cortisol is naturally secreted when we are exercising. It is associated with a sympathetic “fight-or-flight” response, which raises our heart rate, blood pressure, and helps our bodies mobilize our energy stores to power through an intense workout.
Problems arise, however, when cortisol production remains chronically high, especially near bedtime. When cortisol levels are chronically elevated, this can result in impaired physical recovery, leading to symptoms of overtraining such as fatigue and reduced performance.
Since cortisol is a catabolic hormone, when it is chronically elevated it can lead to the breakdown of muscle tissue and negatively impact muscle gains. Like HGH, cortisol interacts with blood glucose and insulin secretion. High levels of cortisol produce more circulating glucose and insulin resistance, leading to weight and fat gain, and in the worst of cases, type 2 diabetes.
Chronically elevated cortisol also aids in the proliferation of “bad bacteria” in the bacterial community in the gut known as the microbiome. A healthy, diverse microbiome plays an important role in regulating nutrient absorption in the digestive tract, as well as regulating body weight, the immune system, and important neurotransmitters. Poor sleep can prevent the meaningful absorption of all food nutrients, and lead to gastrointestinal issues, and impaired post-workout recovery.
Sleep deprivation triggers an overactive sympathetic nervous system, which results in increased levels of cortisol. On the other hand, seven to nine hours of high-quality sleep can reduce cortisol levels and mitigate these destructive effects on our exercise performance and recovery. If high cortisol levels are interfering with sleep, lifestyle practices such as yoga, meditation, and light to moderate exercise earlier in the day can help bring its levels back into a healthy balance.
Adequate sleep boosts cognitive performance and mood, which improves physical exertion
In the best-selling Why We Sleep, author and neuroscientist Matthew Walker explains that sleep is essentially a form of overnight therapy. When we get a good night’s sleep, we are more likely to have a positive mood as well as feel energetic and alert the next day, which can dramatically improve fitness results. When sleep quality and quantity are optimal, our levels of physical exertion are maximally high.
Just one night of poor sleep can cause a large reduction in both the intensity and duration of our workout capacity. If we’re sleep-deprived, we are more likely to have less motivation to complete a workout, our ability to regulate stress is disrupted, our focus is impaired, and our reaction times are slower. Taken together, these factors can also lead to a higher chance of physical injuries if we do manage to exercise the next day.
If we slept well the night before but get poor sleep after a workout, this will not only hinder physical recovery which takes place in deep sleep but will also reduce our ability to learn and refine the skills we may have learned during training. Adequate sleep is crucially important for learning and memory consolidation, and no amount of recovery sleep will regain the losses in this domain.
According to one study published in Sports Medicine, 30-72 hours of sleep deprivation didn’t affect cardiovascular, respiratory, or muscle strength responses. But it did lead to quicker exhaustion times and poorer workouts. The researchers noted that both the increase in insulin resistance and a decrease in glucose tolerance were the main two physiological drivers of this impairment.
In a supportive study of women with insomnia, shorter exercise periods following nights with poorer sleep quality, quantified either as shorter total sleep time or longer sleep onset latency, resulted in reduced exercise duration.
How does exercise influence sleep?
Now that we’ve explored how important sleep is for exercise and recovery, let’s take a look at how exercise influences sleep.
The effects of exercise on sleep can be partially explained by its effects on the production of a chemical called adenosine. At this moment, adenosine is accumulating in your brain (unless you have drank a lot of coffee, which works by blocking the action of adenosine). When there are high levels of this chemical, it produces a sleep drive by making us feel drowsy. Physical activity results in more adenosine accumulation in the brain, which makes it easier to fall asleep.
Physical activity earlier in the day can also raise our body temperature, which subsequently falls a few hours later. When our core body temperature drops, this is a strong signal for our body to initiate sleep.
Decades-old sleep research has established that regular levels of physical activity can increase the amount of deep NREM sleep we achieve on subsequent nights. This makes sense intuitively, since this stage of sleep is where the majority of our bodily restoration and recovery takes place. As we’ll see, exercise has an effect on several other sleep variables, making it an effective treatment approach in those suffering from poor sleep.
Exercise increases multiple sleep variables in healthy individuals
In young, healthy adults, frequent, vigorous exercise is related to increases in total sleep time, especially slow-wave sleep.
Research has also shown that, not only does exercise have also improve sleep quality, increase REM sleep, and lower the percentage of light sleep but also decreases feelings of stress and coincides with fewer mental health problems.
Exercise improves sleep in individuals with sleep disturbances
A 2012 study examined the effects of exercise on the sleep of middle-aged and older adults with sleep problems. A 10-16 week-long exercise training program reduced sleep latency, resulted in better sleep quality, and reduced medication use compared to those without an exercise program.
In one 2010 study published in Sleep Medicine, researchers evaluated the effects of increased physical activity in older adults with insomnia. By the end of the four-month period that included moderate-intensity workouts four to six times per week, the participants were sleeping an additional hour each night.
Subjective sleep quality, sleep efficiency, and sleep onset latency was also improved compared to the non-exercising group. An anti-depressant effect of exercise was also noted by the researchers, who found a better quality of life and reduced depressive symptoms in the physical activity group.
Regular physical activity may also greatly benefit individuals suffering from sleep apnea. Sleep apnea is a serious sleep disorder characterized by stops and starts in breathing during the night.
A wealth of research indicates that regular physical exercise, especially aerobic exercise, can help reduce the symptoms related to obstructive sleep apnea. Regular physical activity supports healthy weight loss, which can reduce the severity of symptoms related to the disorder. Studies have reported that it can also reduce daytime sleepiness, a common result of sleep apnea, and increases sleep quality, sleep efficiency, and maximum oxygen consumption.
Is it bad to workout before bed?
In short: yes, the timing of exercise makes all the difference. As mentioned earlier, exercise raises body temperature by increasing heart and metabolic rate. The rise in body temperature can remain high for a few hours after the workout. If you work out too close to bedtime, the rise can actually prevent you from falling asleep.
This study found that an increase in heart rate as a result of high-intensity exercise before bedtime can lead to a delay in sleep onset. For this reason, it is best to finish working out at least two hours before bedtime. If you do exercise right before bed, it can help to do a longer cooldown and some relaxation and stretching to get your heart rate and body temperature back to normal levels.
How much sleep does an athlete need?
Now that we’ve established how crucial sleep is for physical performance and recovery, you might be curious to hear what elite athletes do. You might be surprised to learn that athletes frequently deal with intensely full schedules containing frequent travel and high stress related to training and performance pressure, which all can have a profoundly negative influence on sleep quantity and quality.
In fact, according to one review, many athletes suffer from insomnia symptoms, daytime fatigue, and fragmented sleep. A whopping 60-70% of athletes get poor sleep the night before a big performance, regardless of how much they have prepared
While most people require between seven to nine hours of high-quality sleep, athletes often require more given the physiological and psychological demands of their demanding lifestyle. Jim Thornton, president of the National Athletic Trainers' Association, suggests athletes in training should aim to sleep about an hour more than the recommended 7-9 hours of sleep per night.
A study from researchers at Stanford University validated this suggestion. They found that students on Stanford University's varsity basketball team who extended their sleep to ten hours per night resulted in faster sprint times, better shooting accuracy, and higher goal percentages.
In light of this study and others with similar results, athletes should aim for at least 8-10 hours of sleep per night. On nights leading up to the performance, ten hours of high-quality sleep may lead to the best athletic performance on game day.
To get better quality sleep, athletes can benefit from optimizing their sleep hygiene to improve their chances of getting the sleep they need to perform.
Can fitness trackers help?
Fitness trackers can be helpful tools for athletes to gain insight on both physical activity and sleep patterns. The best fitness trackers will continually measure your vital signs such as heart rate, count steps, can estimate calories burned, and measure the quality and duration of sleep with a reasonable yet limited degree of accuracy.
Wearable trackers are helpful for athletes because they can help inform workout routines, sleep schedules, and provide data-driven insights on your physical performance. There are some reports that wearable sleep trackers can lead to sleep-related anxiety and sleep perfectionism because the trackers are constantly observing and evaluating sleep data, and sometimes reading out insights that are contrary to what one might expect upon waking. However, they can be a promising addition to any athlete’s fitness toolkit if their limitations are understood.
There are numerous pros and cons associated with commercial sleep trackers. We’ve gone into more depth regarding some of the limitations of sleep trackers in this article.
It’s clear that sleep is the ultimate physical enhancement and recovery period, and it should always be prioritized. If an athlete had to choose between a good night’s sleep and a workout, sleep should always win out as the most important for overall health, wellbeing, and performance.
For non-athletes, just 30-60 minutes of aerobic exercise and resistance training a few times per week can make a great difference in sleep latency, total sleep duration, and the quality of sleep for both healthy people and people suffering from a sleep disorder. Just be sure to get that workout in at least 2 hours before bed to give yourself the best chance of sleep.
Insulin resistance: An inability of the body to release insulin in response to heightened glucose levels. Insulin resistance leads to higher glucose levels in the blood and is intimately connected with metabolic syndrome and type II diabetes.
Catabolic hormone: Catabolic hormones include cortisol, adrenaline, and glucagon. These hormones are involved in destructive metabolism, breaking down fat and muscle for the release of energy,
Microbiome: The totality of microorganisms that inhabit the human body, including bacteria, fungi, protozoa, and viruses. A wide range of conditions is linked to the healthy functioning of the microbiome, from mood disorders like anxiety to obesity and autoimmune conditions.
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