Exercise and Sleep
The link between exercise and sleep
In one of my earlier blogs, I listed sleep as a third pillar of health alongside exercise and nutrition. I noted that while physical activity and eating well are important, our health is maximized when we pair both with a good night’s rest. We’re primed to sleep better if we choose nutritious foods and move our bodies throughout the day, and that relationship is bi-directional – we will move better if we sleep well at night.
The benefits of exercise
Most of us already know that exercise is good for us.
Being physically active can improve your brain health (reducing feelings of anxiety and depression and elevating mood), help manage weight, reduce risk of disease, and strengthen bones and muscles. Exercise also stimulates new brain cell production and your ability to make new neuronal connections for deeper learning and memory.
But how does exercise contribute to good sleep?
The benefits of exercise for sleep
Our bodies need to exert effort during the day so we can feel tired at night. It’s as simple as that.
One of the factors that drives sleep is called sleep pressure, which refers to the amount of time you can stay awake before you start feeling sleepy again, and there are several things that influence sleep pressure. When you wake up in the morning, your sleep pressure is low as you’ve just been asleep, but as the day goes on, it builds and builds so that ideally, at the end of the night, your sleep pressure is high enough that you fall asleep and stay asleep.
I like to imagine that sleep pressure is like a balloon that fills up as the day goes on – so when your day starts there’s no air in the balloon but as you go about your day, there are things you can do to make that balloon bigger like exercise, eating well, and finding ways to relax. On the other hand, there are activities that take the air out of the balloon, or decrease that sleep pressure, such as drinking too much caffeine, getting too much blue light exposure in the evening, and napping. And importantly, sedentary living can make it difficult to build up the sleep pressure we need to fall asleep and stay asleep.
We want our balloon to be nice and full and tight because the higher our sleep pressure is, the more likely we’re able to fall asleep and have good quality, deep sleep. Movement and exercise not only help with sleep, but they also balance critical hormones in our body that are important for mood and function, such as cortisol, dopamine, insulin, thyroid and sex hormones.
Our circadian rhythm is another important aspect that drives sleep and exercise has a huge impact on synchronizing our brain clock and improving arousal and alertness, especially in the morning. Engaging in physical activity also makes it easier for your brain and body to power down at night. Furthermore, sleep can help you see the results of all your hard work and exercise. During deep NREM sleep, our muscles and tissues get strengthened and repaired, optimizing all of our effort at the gym.
When to exercise for the best sleep
Just like sleep, people may have a preference as to when they want to work out – some prefer earlier in the day, others may like an afternoon workout, and there are those who feel more energized in the evening.
However, if you’re having trouble getting to sleep at night (and you’re not a high-functioning night owl), earlier in the day is ideal. Working out too close to bedtime might be too mentally and physically stimulating, leaving your nervous system feeling wired and making it difficult to calm down at night and get to sleep.
Furthermore, if you’re engaging in high intensity cardio activity, your core body temp will rise but for optimal sleep conditions, your body’s temperature should be low. Your core body temperature changes throughout the day – it’s typically at its lowest a few hours before you wake and it’s highest an hour or two before bed. The changes in temperature affect your alertness, muscle strength, and flexibility, as well as your sleep-wake cycle. When your core temperature drops at night, it triggers the release of melatonin and signals to the brain that it’s time to get sleepy.
But everyone has their energy spikes and dips at different times. Exercising at the right time for YOUR body has been shown to minimize post-workout cortisol spikes (and cortisol spikes = stress). In other words, "morning people" who work out in the morning have lower cortisol spikes after exercise. Similarly, those who get a second wind of energy in the evening also have less dramatic rises in cortisol if they do their exercise at that time. People who exercise outside their peak time experience the biggest increases in post-workout cortisol as well as poorer performance. So, it’s a delicate balance of finding time within your schedule to work out that fits with your body’s natural inclination to do physical activity. If you’re not sure when the best time to work out for you is (and you’ve got some flexibility) run your own experiment. Try exercising earlier in the day for one week and see how you feel, then the next week go for a lunchtime workout, then the following week try an evening exercise, and observe if one time of day makes a difference to your daytime energy levels and night time sleep.
The perks of exercising outdoors:
Ideally, getting outdoors and working out within 30 minutes to 2 hours before or after sunrise will help set off a cascade of benefits to your sleep later in the evening:
Getting daylight exposure first thing in the morning helps sync up your brain’s internal clock (think circadian rhythm that regulates your sleep/wake cycle)
Natural sunlight activates the blue sensors in your eyes, and as you exercise, the sensors will fire up your brain and increase alertness (and reduce depression)
On colder days, you activate brown fat and increase your fat burning potential
You naturally raise your cortisol to a healthy level in the morning, which will lower inflammation (and inflammation can affect the sleep centers of your brain)
If you can’t get outside and do a full cardio routine first thing, even a short 15-minute walk outside in the morning and at lunchtime can boost your mood, energy levels and strengthen your circadian rhythm. Natural sunshine will continue to send alerting signals to your brain that it is daytime. And remember to take those sunglasses off as they will filter out those important light waves you need! In the evening however, to further regulate and strengthen your sleep/wake cycle and prepare your body for rest, you should minimize that bright light exposure. Remember, melatonin, the sleep hormone, is triggered by darkness so too much evening light may send a signal to your brain that it is still daytime.
Calming evening exercises:
Not all evening exercise is detrimental to your sleep health. If you’re a night owl and go to bed past midnight, there’s nothing wrong with an 8pm kickboxing class. Exercise can be a productive activity to release some energy before starting to wind down for the night. However, if you notice that certain types of exercises get your heart rate up too much and as a result, you find it difficult to fall asleep, try engaging in a less intense form of movement. Leisurely, moderate-intensity workouts and mind-body activities can be especially beneficial for getting a good night’s sleep. These include:
Yoga
Tai chi
Resistance training
Light Aerobics
Walking
Stretching
A good all-around practice for night-time workouts is to end them with deep breathing exercises. Diaphragmatic breathing, also known as belly breathing (as opposed to shallow breaths coming from the top of our chest) can reduce cortisol levels by activating your parasympathetic system – the rest and digest state that our bodies need to get into for sleep. If we’re overly stimulated and taking quicker, shallower breaths, our fight or flight response will kick in, raising alertness and cortisol levels and putting our bodies in a less conducive space for rest.
