What if someone sincerely dislikes exercise and works out only under a kind of emotional duress, deeming that he or she must do so, perhaps because a doctor or worried spouse has ordered it?
In that case, which is hardly uncommon, does the stress of being, in effect, forced to exercise reduce or cancel out the otherwise sturdy emotional benefits of physical activity?
That issue has been of considerable interest to exercise scientists for some time, particularly those who work with animals, since in some experiments, animals are required to exercise at intensities or for durations that they don’t control. Such intense exercise greatly increases their stress, as measured by certain behaviors and by physiological markers like increased levels of the stress hormone cortisol.
But no study had directly compared the emotional effects of forced and voluntary exercise on anxiety and emotional resilience.
So scientists at the Center for Neuroscience at the University of Colorado at Boulder recently decided to conduct one.
They began by gathering a group of healthy adult male rats of a type that generally enjoys running.
Then they gave some of the animals access to unlocked running wheels and let them exercise whenever and for as long as they liked. The exercise was fully under the animals’ control.
The scientists tracked how long and in what pattern the animals chose to exercise, noting in particular that the rats tended to skitter frantically for brief periods, slow down, then speed up again — rather like people alternating jogging and walking or completing intervals.
Having determined how the animals spontaneously liked to run, the researchers next placed other rats in mechanized, lockable wheels that were controlled exclusively by the scientists.
The scientists then forced these rats to run. To the extent possible, the researchers mimicked the animals’ normal, spontaneous exercise pattern, having the rats run during the portion of the day when they naturally would be active and creating frequent stops and starts in their running, just as the rats that ran freely had done.
The animals’ daily mileage was equivalent to that of the voluntary runners.
Meanwhile, a third group of rats ran on little mechanized treadmills, at a steady, even pace, without fits and starts of voluntary running. The animals could not control their speed or distance.
A final group remained sedentary.
All of the animals exercised, or lounged, for six weeks.
At the end of that time, the animals were exposed to experiences that are known to cause stress and worry in rats, like being restrained.
The next day, the animals were placed in a large, unfamiliar mazelike cage designed to determine their levels of anxiety or confidence. If they froze or scurried to the darkest corners of the cage and refused to explore, they were considered to be highly anxious and unsettled, by rodent standards.
The treadmill runners and the sedentary animals were, the results showed, extremely anxious. They froze or ran for the darkness at the first opportunity.
But the animals that had exercised on the running wheels, whether they could control their exercise regimens or not, proved to be quite resilient. They bounced back emotionally from the imposed stresses and were willing to explore the lighted regions of their new surroundings on the next day.
They were, by rodent standards, happy and well-adjusted guys.
What this suggests, says Benjamin Greenwood, a professor of integrative physiology at the University of Colorado who designed and led the study, is that “even forced exercise increases stress resistance.”
If, in other words, you are being cajoled to exercise, whether by your conscience, by your partner or by some other overriding force, you nevertheless are likely to wind up feeling less anxious, more relaxed and happier afterward, even if you’re not having fun during the workout.
Of course, rats are not people, and no comparable experiment has been performed in people, Dr. Greenwood says.
It’s also unclear, he says, why the forced treadmill running did not confer stress resistance, although he suspects that the reason lies in the way the animals ran. The treadmill runners were not allowed to start and stop, but had to run continuously at a steady pace.
This finding doesn’t necessarily mean that alternating between walking and running will make people happy, he says. But it does intimate that how you exercise might add to a workout’s emotional impact and that perhaps experimenting with a pattern of slowing and speeding up during a run or bike ride could be worthwhile.
More important, though, the study is a useful reminder that exercise is a proven, inexpensive and non-pharmacological means of combating stress — even, as it turns out, the stress of feeling that you should be exercising, Gretchen Reynolds on the science of fitness.