Exercise and Sleep Quality – Sleep Series Part 4

Gillian White, MSc., PhD (Candidate), University of Toronto, Graduate Department of Exercise Sciences

Sleep Stats And General Information – Sleep Series Part 1

Sleep Physiology – Sleep Series Part 2

Sleep And Health – Sleep Series Part 3

Exercise and Sleep Quality – Sleep Series Part 4

There is lots of research that shows improved sleep quality is one of the many secondary benefits of exercise, beyond those of just fitness and body composition. From children to older adults, healthy individuals to patients of all types of ailments, exercise seems to help us sleep better. This is one of the most overlooked health benefits of exercise – optimizing rest so that you’re contributing to your health even when you aren’t awake. Sleep is so important for how our brain and body feel and function. Nearly 30% of adult Americans report insufficient sleep. Sleeping pills come with adverse effects and they shouldn’t be taken on a long-term basis. That leaves exercise as one of the only long-term solutions for resolving sleep deficiencies.

So, what is it about exercise that helps us sleep better and are all types of exercise created equal? Is getting a good sweat just inherently good for sleep or are the cumulative effects of exercise-induced fitness changes at the root of improved sleep quality? This section will explore the benefits of HIIT, aerobic exercise, resistance training, and low-impact exercise on sleep quality and try to uncover just how exercise helps us sleep (see figure 1.)

How Does it Work?

In general, when you exercise, you improve your sleep quality that night by straining your brain, decreasing your body temperature, and increasing parasympathetic drive. Physical effort takes a lot of mental work! You expend energy pushing your body when it wants to quit, and use up existing energy stores in the body, which contribute to the homeostatic drive to sleep. This helps you fall asleep earlier and promotes slow wave sleep (labeled ‘CNS fatigue’ in figure 1.).

When you exercise, your body temperature increases with the metabolic effort you exert. You have a set body temperature range that your body wants to maintain where cells function the best (98.6°F; 37°C). When you take your body temperature above that range, your body makes adaptations to bring it back down, usually overshooting and dropping your body temperature lower than before you started your exercise. The lower body temperature helps you get into a deeper sleep and, like the CNS fatigue, helps promote slow wave sleep leaving you feeling well-rested in the morning. Better body temperature regulation is also one of the contributing factors to better sleep quality with regular exercise. As the insulating effects of excess subcutaneous (under the skin) fat is lost and metabolic changes promoting efficiency at the cellular level occur, heat production at rest is regulated better.

Post-Exercise Effects

Similar to the reflexive overcompensation of body temperature after exercise, changes in sympathetic/parasympathetic nervous system balance have delayed post-exercise effects. During exercise, your sympathetic “fight or flight” system is activated and parasympathetic drive is reduced. This helps support exercise by increasing heart rate, blood pressure, breathing rate, and muscle activation. When you finish your exercise, the reverse happens: parasympathetic drive increases and sympathetic drive decreases. The parasympathetic switch can be observed as lower heart rate and blood pressure but it also contributes to a restorative and repair processes in the body that are less noticeable. Autonomic nervous system balance is also a contributor to long-term adaptations with increased physical fitness and one of the reasons that training programs help you sleep better on the regular. It’s also part of why athletes have low heart rates.

Cental Nervous System Fatigue

It’s important to note that these reflexive changes in body temperature and parasympathetic activity, and the central nervous system fatigue that contribute to better sleep during the night after your exercise take some time to take effect. So, exercising within a couple hours of bedtime can actually make it harder to fall asleep. This is important when you’re timing your exercise, especially if you’re hoping to improve your sleep quality with your exercise program.  

Figure 1. Acute and chronic changes induce by exercise that promote sleep quality. (From Uchida et al. 2012).

1. Aerobic Training and Sleep

Aerobic exercise has been long thought to improve sleep quality. The relationship between aerobic activity and sleep has come from observations that aerobically fit people fall asleep faster, have deeper sleep, and sleep longer (Edinger et al., 1993; Baekeland & Lasky, 1966). Higher self-rated sleep quality has been reported in people who also report recent increases in activity, while the reverse is seen in people who report reduced physical activity (Sherrill, Kotchou, & Quan, 1998). The rationale behind sleep improvements with increased aerobic activity are based in the effects of aerobic activity on fatigue and body temperature. The most common changes reported with increased aerobic activity are the same for those reported in aerobically fit people: increased slow wave sleep (deep sleep), total sleep time, and decreased REM sleep, as well as increased wakefulness during the day (feeling more alert).

Effects on Depression

A study of 50 to 76-year-old men and women participating in a community-based moderate intensity exercise program (low-impact aerobics or brisk walking at ~60-75% of heart rate reserve) resulted in improved sleep quality measured by a sleep questionnaire (Pittsburgh Sleep Quality Index) (King et al.1997). In people reporting poor sleep associated with depression, improvements in both sleep quality and depressive symptoms were improved. While both sleep and depression can independently benefit from aerobic exercise, the authors were unable to determine whether exercise improved sleep directly or whether reported improvements in sleep were a result of reduced depression (Singh et al. 1997).

I Want Results…Now!

Exercise programs improving fitness seem to help sleep but what about the acute effects of aerobic exercise today on sleep quality tonight? The acute effects of exercise seem to agree very well with the chronic effects of aerobic exercise. Acute aerobic exercise increases sleep duration by ~10min decreases REM sleep and increase stage 4 slow wave sleep (the most coveted of deep sleep) by ~4 min (Driver, 2000). The duration and intensity of exercise are important factors in the effects it will have on sleep. Longer exercise (>30 minutes) and intense exercise seem to drive the greatest improvements in sleep quality (Youngsted O’Connor, & Dishman, 1997). Since exercise also has transient effects on alertness, exercise close to bedtime (i.e.

Aerobic Exercise For Sleep

Although the importance of aerobic activity on sleep quality is widely reported in anecdotal reports, there are seemingly lower effects in smaller, interventional studies. The reason for this appears to be the people included in the intervention studies who may already be aerobically fit or already have high sleep quality – so called “good sleepers”. In research, this is called the “ceiling effect” where the people being studied have little room for improvement in the intended outcome of the intervention. Therefore, aerobic exercise and/or improvements in aerobic fitness are most likely to improve sleep in people who need to improve their sleep! Hence, older individuals, women, sedentary individuals, or people who report high stress and/or low levels of physical activity (Uchida et al 2012).

Aerobic exercise for sleep:

Demographic Factors – who will benefit the most?

• Women
• Older individuals
• Sedentary individuals
• Depressed or stressed individuals

Exercise Factors:

• Timing of exercise – should be done >3h before bed
• Duration of exercise – should be >30 minutes
• Intensity of exercise – should be >65% HRmax

2. High-Intensity Interval Training (HIIT)

Exercise intensity is one of the acute factors influencing sleep effects after exercise, as is aerobic fitness changes. HIIT includes high-intensity bouts interspersed with active rest bouts of a lower intensity. HIIT includes not only sprint-like activities (i.e. spin class, track workouts) but also metabolic conditioning classes like Tabata workouts. This type of exercise induces significant fatigue (both mental and physical) and is extremely effective at improving aerobic fitness. Because of this, it is thought to be an effective exercise method for improving sleep quality and quantity.

No studies have investigated the effects of HIIT in healthy participants. However, given the effects of HIIT on aerobic fitness, one may expect them to be similar, if not slightly greater, than those observed in traditional aerobic training regimes. In participants with co-morbidities involving sleep disturbances, such as rheumatoid arthritis and sleep apnea, the results of HIIT programs appear promising. Rheumatoid arthritis and other inflammatory illnesses are commonly associated with sleep disturbances. And these are thought to exacerbate pain and symptoms of dysfunction.

Inflamation and HIIT

There is a bi-directional relationship between inflammation and sleep in which inflammation disrupts sleep, while good sleep quality reduces inflammation. HIIT can independently improve sleep and inflammation, effectively improving disease-related outcomes (Loppenthin et al. 2014). HIIT in sleep apnea patients also shows promising results. After a 12-week HIIT program in obese sleep apnea patients, aerobic fitness was improved, apnea related events were reduced, and daytime sleepiness was reduced compared with controls (Karlson et al. 2013).

Timing and HIIT Takeaways

As with aerobic exercise, the time of day the HIIT is performed determines its effect on sleep that night. In healthy soccer players, it was found that HIIT training done in the evening disrupted sleep while HIIT in the morning did not (Vitale et al. 2017). Another interesting element of the sleep <–> HIIT relationship is the effect of sleep on quality of HIIT training. Quality sleep is needed to allow maximal mental effort for both intellectual and physical activities. Because of the high intensity required of HIIT, poor quality sleep will have negative effects on the quality of your workout, limiting the intensity that you can muster and increasing the feelings of relative exertion of the exercise (McMurray & Brown, 1984).

Overall, the guidelines for HIIT and expected outcomes on sleep quality and duration are similar to those of aerobic training. Improvements in aerobic fitness, night-time fatigue, and reflexive parasympathetic activation can help you fall asleep faster, and get a longer, deeper sleep. In people with illnesses with symptoms of sleep disruptions, inflammatory status and aerobic fitness improvements (and likely parasympathetic/sympathetic system balance) can be improved by exercise, subsequently improving sleep symptoms.

3. Resistance Training

HIIT and aerobic exercise have similar physiological effects on the body. Therefore, can be expected to have similar effects on sleep both acutely and chronically. But what about weight training? Traditional resistance training doesn’t impose the same metabolic demands that aerobic or HIIT training do. Nor does it elevate core temperature to the same extent. With that said, depending on your intensity, a considerable cognitive effort is required to get through the last reps of a set and autonomic balance shifts towards parasympathetic during recovery. So, there is a reasonable physiological rationale for resistance training to improve sleep quality. On the flip side, excessive weight training that causes high levels of cortisol or muscle damage and pain can interfere with sleep. And as you may know, it’s hard to get comfortable when you can’t move from your workout.

Research investigating the effects of resistance training on sleep quality is more limited than for aerobic. However, it generally points towards improved sleep quality, especially in populations with poor sleep. In a group of older people with reported sleep difficulties, a 24-week resistance training program resulted in increased total strength (19%), upper body strength (52%), and sleep quality (38%) (Ferris et al. 2005). The regimen used was fairly moderate: 50% 1 rep max load was used in a circuit that included bench press, leg press, leg curls, leg extension rowing, shoulder press, and arm curls, and only took about 30 min.

Mixing Programs for Positive Results

Similarly, in older adults with depressive symptoms, a resistance training 3x per week for 10 weeks improved sleep quality, depressive symptoms, and quality of life. Statistical modeling was used to determine the predictive variables of effects found from the program. Consequently, it found improvements in strength and improvements in general depressive scores were most strongly predictive of sleep improvements (Singh 1997). No mechanistic studies have been conducted for how resistance training improves sleep, but the limited evidence shows benefits.

Some studies have included mixed aerobic and strength programs with positive results (Kline et al 2011). While both aerobic, HIIT, and resistance training seem to all improve sleep, it raises the question: Is there a type of exercise that is best? An intervention study to answer this has not been yet been conducted. However, compared with power lifters, endurance athletes have higher SWS increased sleep duration and shorter sleep onset (Trinder, Mongomery, & Paxton, 1988; Trinder et al., 1985). Therefore, if you’re really keen to get a change in sleep quality from your exercise, make aerobic training your priority.

4. Low Impact Exercise

As was stated at the beginning of the exercise section of the sleep series, the most likely cause for exercise’s effects on sleep are:

1. Hot core temperature during exercise resulting in reflexively lower temperature later (cooling the body facilitates deep, slow wave sleep – kind of like hibernation).
2. Metabolic fatigue of the brain (and body) – exercise is hard! Not just for the body but for the brain too. The mental exertion of persevering through bodily discomfort paired with the overall fatiguing effects of exercise, help drive you to fall asleep faster. This means less time tossing and turning before drifting off.
3. Autonomic nervous system balance – Intense exercise activates the sympathetic “fight or flight” arm of the autonomic nervous system. With the Fight or flight stimulus removed (i.e. when your workout is done), the balance shifts towards turning off the activating sympathetic system, while turning on the repair and recovery parasympathetic system.

Because low-intensity exercise by its very definition is not likely to cause excessive fatigue, core temperature increase, or fight or flight drive, how can it improve sleep?

Low-Impact Exercise and Mindfulness

Low-intensity exercise like Pilates, yoga, and Tai Chi, commonly involve some level of strength and aerobic demand. However, this is generally at relatively low levels. So, it’s more likely that the combination of controlled movement, mindfulness, and deep breathing involved in these practices that drive an increase in parasympathetic activation. And this promotes rest and recovery and facilitate slow wave sleep. There is a strong body of evidence to show that these types of low-intensity exercise practices reduce anxiety, stress, and other acute psychological disturbances. These disturbances can get in the way of sleep.

A study of college students undergoing a Pilates and Taiji Quan program for a semester as a mindfulness-through-movement program found improved sleep quality correlated with increases in mindfulness (Caldwell et al 2009). Consequently, this aligns with studies showing reductions in anxiety and stress reported with these types of exercises as responsible for the improvements in sleep.

Bringing It All Together

The benefits of exercise on health and wellness are far-reaching and include improvements in sleep quality. Exercise can improve your sleep the night after exercise, as well as habitually with regular exercise. All types of exercise are likely to improve sleep quality. However, aerobic exercise or HIIT training seem to be the most effective. This is especially true in populations with sleep disturbances. The immediate changes that promote sleep relate to mental/physical fatigue that helps you fall asleep faster. Furthermore, reflexive decreases in body temperature and autonomic nervous system activation help you sleep deeper.

We commonly associate regular physical activity with better sleep. This is likely because of reductions in inflammation, improved autonomic nervous system balance, and decreased psychological stress, anxiety, or depression. It also probably promotes adoption of healthier habits. Examples of healthier habits include cutting back on drinking or smoking (which can hinder sleep) and eating better. Overall, exercise does more than just make us “fitter.” It keeps us healthy even when we aren’t moving.

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