Sleep has a greater influence on exercise than the other way around, at least in the short term - this is the conclusion reached by researchers at the Feinberg School of Medicine at Northwestern University.  The effects of daily exercise on sleep patterns is more complicated than previously thought, however.

Researchers were frequently met with the complaint that after regular, strenuous exercise patients slept no better than before.  As a result they began poring over the results of one of their previous studies.  For that experiment, researchers had gathered a small group of women who had received diagnoses of insomnia. The volunteers were mostly in their 60s, and all were sedentary.  They were then divided into two groups.  One group continued with its sedentary lifestyle, while the other began a moderate endurance exercise program, consisting of three or four 30-minute exercise sessions a week.  This exercise program continued for 16 weeks.  The results clearly showed that exercise helped in overcoming insomnia.  The changes, however, only became evident at the end of the experiment.  For the first two months of the 16 week study regular exercise on a stationary bicycle and treadmill had no positive effect on either the length or the quality of sleep.  In fact sleeping badly tended to shorten the next day's workout, while a full, intensive workout did not produce better sleep that night.

In the end those suffering from difficulties with sleep can only count on improvement in the long term, after 3-4 months, insofar as they exercise regularly.  Then, on the other hand, they can expect the duration of their sleep to increase by at least 45 minutes with fewer periods of wakefulness at night, a sound and healthy alternative to medications aimed at achieving the same result.