Music played during an aerobic dance class often relieves the mental stress of exercise, according to the Reebok Aerobic Information Bureau. It says Ohio State University researchers had nine men run on treadmills for 30 minutes. First, they listened to upbeat rock music. Then they exercised without music. When they ran with musical accompaniment, the exercisers felt they had exerted themselves less. Also, they had lower levels of betaendorphin, a natural opiate the brain releases in response to stress or pain.