To learn more, Dr. Meyer turned to stored blood samples and other records from a relevant earlier experiment. That research, which he had conducted as a doctoral student at the University of Wisconsin, had involved women with major depression completing a number of workouts on stationary bicycles.
Each of the workouts lasted for 20 minutes, but their intensities varied substantially, from light to draining. During most of the sessions, the women were told how intensely to pedal, with their efforts monitored and adjusted so they maintained that level. But during one workout, they could choose the intensity, pedaling as easily or strenuously as they liked.
Before each session, the women gave blood and completed questionnaires about their emotional states. Immediately afterward, they gave blood again and, 10 minutes and 30 minutes later, repeated the questionnaires.
In earlier studies using data from this experiment, Dr. Meyer reported that any exercise, whether its intensity was light or difficult, left the exercisers feeling more cheerful. However, the positive impacts tended to be more substantial when the women followed directions about how intensely to exercise compared to when they set their own pace.
Now, for the new study, recently published online in Medicine & Science in Sports & Exercise, Dr. Meyer set out to see if any changes in the women’s endocannabinoid levels after the different sessions might have played into that dynamic. For the sake of a simple comparison, he focused on one session in which the women had cycled continuously at a moderate pace and another in which they had pedaled at whatever intensity they chose. For most, their you-pick effort was gentle; but for others, it was moderate, and for a few, intense.
And he found notable differences in outcomes. After both workouts, the women reported feeling less depressed and worried. But only when they had followed instructions to pedal moderately did their blood show increases in endocannabinoids. When they had exercised at their preferred pace, even if it was moderate, endocannabinoid levels remained unchanged.
What these results suggest, Dr. Meyer says, is that being coached and supervised leads to different impacts on our bodies and minds than working at our own pace, whatever that pace might be.