Does exercise make it easier or harder to get to sleep? As in so many things involving sleep, the answer is both.
More often than not, exercise is good for your health and improves sleep quality. Sometimes it decreases sleep latency (e.g. you get to sleep faster) and increases sleep efficiency (e.g. you won't be awake so much in bed). Some people are not healthy enough for exercise (check with your doctor) and even in people who are, heavy exercise sometimes results in middle-of-the-night awakenings. These might be due to hyperarousal (hard to relax) and/or increased adrenaline levels during the night following aerobic exercise. Increased body heat could also make it difficult to sleep.
Light aerobic exercise and anaerobic exercise such as lifting weights almost always increases sleep quality. If you are really interested in how exercise affects your sleep and how different types of exercise make you feel later that night, we encourage you to keep a sleep diary. Just a few data points may give you some insight about the type, intensity, and duration of exercise can help you.
The federal government (National Institute of Health) says 5 to 6 hours before bed exercise should be avoided during this time. This is intended as a very general guideline. The actual time differs from person to person. Strenuous exercise can make you sleepy. Lifting weights, for instance, when you haven’t been lifting in a while, makes most people sleepy.
Why should exercise make it easier to get to sleep or make the quality of sleep better? Is this a product of the "restorative" function of sleep - better rest? If so, that is thought to be a minor reason. Your muscles can rest while you are awake sitting on the couch watching television. it enhances/reinforces swings in your daily cycle, with increases in blood pressure, metabolic activity, and overall feeling of being alive. The "up" of exercise makes the "down" the following night feel lower and mitigates the feeling of hyperarousal that might cause insomnia.
Both aerobic and anaerobic exercise stimulate release or more growth hormone during the following night. Interestingly, it has been shown that the diminishing returns happen sooner with anaerobic exercise than with aerobic: i.e. if you increase the duration of your run you increase the boost in hormone release more than if you increase the duration of your weight-lifting session. http://europepmc.org/abstract/med/24576855
A study in India looked at the effect of exercise on sleep quality in elderly people. It concluded both anaerorbic and aeronic exercise promoted sleep quality, and that aerobic exercise was better.
Exercise is like a warm bath in that both are skeep hygiene/lifestyle choices that can make sleep better and which do not involve drugs. Why should a bath help with sleep? The bath (even in warm water) lowers body temperature and thereby signals the body to start sleeping in the evening – in conjunction with the circadian cycle.. But doesn't warm bath water increase body temperature? No. Even a warm bath is cooler than body temperature. Further, after you exit the bathtub evaporation of residual water carries away heat and cools down your body.