"This is the first time we've been able to document this kind of enhancement associated with exercise," said Charles Emery, a professor of psychology and the lead author of the Ohio State University study.
The faster that a wound heals, the less chance it will become infected.
The results appear in a recent issue of the Journal of Gerontology: Medical Sciences.
The study included 28 healthy older adults ranging in age from 55 to 77 (average age was 61). The participants hadn't exercised regularly for at least six months prior to the study. For the research, about half (13) of them exercised three times a week for three months. The other 15 participants served as controls and were asked not to change their physical activity habits during the study period.
Each subject received a small puncture wound on the back of the upper arm. Adults in the exercise group started working out about a month before the wound procedure; this gave their bodies enough time to adapt to a regular exercise program.
The wounds were about 1/8-inch across and deep. The researchers photographed the wounds three times a week until the wounds were no longer visible (about six to seven weeks).
The exercise sessions began with 10 minutes of warm-up floor exercises and stretching followed by 30 minutes of pedaling on a stationary bike. After that, participants either jogged or walked briskly on a treadmill for 15 minutes, followed by about 15 minutes of strength training. All sessions ended with five minutes of cool-down exercises.
Each participant completed assessments of exercise endurance and stress at the beginning and end of the study. The exercise endurance test, completed on a treadmill, measured each subject's aerobic fitness level by measuring how much oxygen he or she consumed while working out.
The researchers also collected saliva samples from each participant in order to measure levels of cortisol, a primary stress hormone. High cortisol levels indicate that the body is under stress; prior studies have suggested that exercise is associated with lower levels cortisol.
Lastly, each subject completed a questionnaire called the Perceived Stress Scale. This scale let the researchers determine how stressful the respondents perceived their lives to be.
At the end of the study, the researchers found that skin wounds healed an average of 10 days faster in the people who exercised (29 days in the exercise group vs. 39 days in the non-exercise group.)
Not surprisingly, exercise endurance increased in the group that worked out, but remained the same in the non-exercise group.
The researchers were somewhat surprised to find a sharp increase in cortisol levels in the exercise group. The hormone is typically boosted by stress, and other studies have suggested that exercise may lower levels of stress.
"The stress of exercise may enhance the regulation of cortisol," Emery said. "This increase in cortisol levels may represent a biological pathway by which exercise helps wounds heal."
There were no changes in perceived stress in either group but none of the adults in this study reported any significant distress in their lives at the beginning of the study.
The current study supports the results of a related study on wound healing conducted at Ohio State a few years ago. That work compared wound-healing rates between older adults caring for a loved one with Alzheimer's disease to rates of older adults who weren't caregivers.
The healing rates of those who weren't caregivers was similar to the healing rates of the non-exercisers in the current studying – wounds in both groups healed in about 40 days. Wounds among older caregivers took about 20 percent longer to completely heal.
"The findings from both studies indicate that the effect of exercise we found in the current study truly represents an enhanced rate of wound healing in older adults," Emery said.
The next step is to determine if older adults who report a fair amount of stress in their lives – such as dealing with the death of a spouse or financial troubles – get the same kind of benefit from exercise.