Giselle S. Passos of Federal University of Sao Paulo in Brazil divided 36 patients -- eight men and 28 women -- with primary chronic insomnia into three experimental groups -- moderate aerobic exercise, heavy aerobic exercise and moderate strength exercise -- and a control group.

After the exercise session, reductions were shown in sleep onset latency, or the length of time it takes to fall asleep -- 54 percent -- and wake time -- 36 percent -- in the moderate aerobic exercise group, while increases were shown in total sleep time -- 21 percent -- and in sleep efficiency -- 18 percent.

In the moderate aerobic exercise group, 37 percent had a significant increase in total sleep time and 40 percent reduced their sleep onset latency. In addition, a significant reduction in the anxiety state was also observed after moderate aerobic exercise.

The findings were presented at the 22nd annual meeting of the Associated Professional Sleep Societies in Baltimore.