Do you have trouble sleeping at night? Do you find it hard to slow down and fall asleep after a hectic day? If you have trouble sleeping, you are not alone. According to the National Commission on Sleep Disorders Research, over 40 million Americans have chronic sleep problems, and over 20 million more experience periodic insomnia. Most runners assume that training leads to improved sleep (we look like we're about to fall asleep much of the time). But, is there scientific evidence that exercise improves the quantity or quality of our sleep?
A study on sleep and exercise conducted in Finland found that 43% of subjects who increased their exercise over the previous 3 months reported improved sleep, and only 1% had a sleep decrement. In addition, 30% of subjects who reduced their exercise over the previous 3 months reported poorer quality or reduced duration sleep while only 4% reported improved sleep. These results certainly support the notion that increased exercise leads to improved sleep. This evidence should be interpreted with caution, however, because we do not know whether the exercise caused the improved sleep, or whether improved sleep made these individuals feel like exercising more.
Another study, by John Trinder, Ph.D., and colleagues in Australia compared the sleep habits of trained distance runners (average of 45 miles/wk), serious weight lifters (12 hours/wk), and sedentary folks. The runners fell asleep more quickly after going to bed and experienced a longer duration of deep sleep than the individuals in the other 2 groups. In other words, the runners had greater sleep efficiency, which is the ratio of the amount of time you are asleep to the total amount of time you are in bed. So, if you are an efficiency freak, you can rest peacefully knowing that you may gain back some of the time you spend running by taking less time to fall asleep.
How does exercise lead to improved sleep?
No one knows for sure, but the mechanism may be a change in the balance of sympathetic to parasympathetic nervous system activity. Stimulation of the sympathetic nervous system increases heart rate, blood pressure, metabolic rate, and mental activity, all of which are counterproductive to falling asleep. Parasympathetic activity has the opposite effect. During running, sympathetic activity increases, but endurance training leads to a decrease in sympathetic activity relative to parasympathetic activity when you are not exercising. This alteration in the balance of sympathetic to parasympathetic activity may allow us to fall asleep more quickly and to sleep more deeply. Running too close to bedtime, however, can leave the sympathetic nervous system stimulated for several hours making it more difficult to fall asleep.
Sleep and overtraining
On the extreme end of the exercise spectrum, anecdotal evidence suggests that overtraining interferes with sleep. Back in my marathoning days, I remember lying in bed at 3 a.m. exhausted from the previous day's intervals and thinking about the next day's 20 miler. The physical and psychological stresses of training beyond your individual threshold may stimulate the sympathetic nervous system, leading to irritability and reducing the quality and quantity of sleep. In fact, a change in sleeping habits is an early warning sign of overtraining.
A reduction in sleep is a double-edged sword for a runner because much of the body's recovery and rebuilding occurs during sleep. If you train hard you need to be particularly careful about getting adequate sleep, or you may experience a decline in performance, immune system depression, and be more prone to injury. If you sleep well most of the time, however, you do not have to worry if you have trouble sleeping the night before a race. There is no evidence that one poor night's sleep is detrimental to performance.
When you have uncharacteristic difficulty sleeping, you could be training hard too frequently. You may be able to improve your sleep fairly easily by backing off your training and not running too late in the day. The harder you exercise, the greater the stimulus to your nervous system, so cutting back your training intensity will likely benefit your sleep more than cutting back your mileage. In addition, if you are having trouble sleeping, see if you can identify any other factors outside of your running that may contribute to your insomnia. Your new boss or that pint of mocha ice cream before bed may be responsible. Naps can also interfere with a good night's sleep. Napping can get you into a cycle of difficulty falling asleep at night, napping in the afternoon, and then having trouble sleeping the next night.
To improve your sleep patterns, develop and stick with a routine that works for you. The mind and body love routine. Eating dinner and going to bed at approximately the same time each day will help to set your body clock, so that your body and mind automatically shut down at the same time each night. Avoid bright lights at night, and avoid lying down until you are ready to go to sleep. Then, when you do lie down, that will be another signal to ease your mind towards sleep.
(This column originally appeared in Running Times Magazine.)