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By Michael Childs
mchilds@coe.uga.edu
Many people find that they sleep better after exercise. But what about when the exercise results in muscle pain? Researchers in the College of Education have found--perhaps surprisingly--that muscle pain caused by exercise does not disturb sleep.
The findings, published in the spring issue of The Journal of Pain, are important because these experimental results differ from what was found in less well-controlled previous studies and challenge the notion that people who are experiencing muscle pain always suffer from an associated sleep disturbance.
People experiencing pain, such as those suffering from arthritis or chronic low-back pain, often report sleep problems. A 1997 Louis Harris poll reported that nighttime pain and sleeplessness affects about 15 million Americans.
“This investigation extended prior research by taking pain-free men and caused them to have muscle pain via exercise. The experiment showed conclusively that exercise-induced muscle pain does not cause sleep problems,” says Patrick J. O’Connor, an associate professor in exercise science and co-author of the study. “This is good news for people suffering from muscle pain who would rather not take nighttime pain medicine.”
O’Connor and two former UGA students, Michael J. Breus and Stephen T. Ragan, conducted an experiment examining the effects of eccentric muscle actions on sleep.
Eccentric muscle action occurs when a muscle produces tension while increasing in length. When a person raises a glass to take a drink, the biceps muscle in the upper arm decreases in length; this is called a concentric muscle action.
When the glass is lowered again, the biceps muscle performs an eccentric muscle action. High-intensity, unaccustomed eccentric exercise results in small tears in the muscle and in muscle pain. The pain usually sets in about 6-12 hours after eccentric exercise and peaks after 24-48 hours.
The study participants, nine young adult men, slept overnight in a sleep laboratory, performed a strenuous bout of eccentric exercise the next day, and then slept in the lab on two additional nights, according to O’Connor.
The exercise involved three different muscle groups--biceps, triceps and quadriceps. Eight sets of 10 repetitions were completed for each muscle group, all at an intensity equal to 80 percent of each participant’s maximum. The eccentric exercise bout took approximately two hours to complete and resulted in moderately intense muscle pain, ranging between 30 and 50 on a 100-point pain scale.
Despite their arm and leg muscle pain, the men did not take longer to fall asleep nor did they wake up more often in the night or have more slow-wave sleep.
“The findings also imply that people suffering from exercise-induced muscle pain who are losing sleep should consider investigating other reasons why they may be experiencing sleeplessness,” says O’Connor.
Ragan, who graduated from UGA this spring, was an undergraduate student in biology at the time of the study. Breus, who completed this investigation as part of his doctoral dissertation under O’Connor, is now a psychologist with the Sleep Disorders Center at Dekalb Medical Center in Decatur.
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