If you suffer from depression, you've likely been advised to get plenty of exercise. Scientists have now gained a fresh understanding of how being active helps alleviate the condition, and they believe that their findings could lead to better treatments.

In a study led by Iowa State University's Asst. Prof. Jacob Meyer, 17 women who had been diagnosed with depression were tasked with completing two 30-minute exercise sessions on a stationary bike. One of these sessions was performed at a prescribed moderate intensity, while the other was done at an intensity of the test subject's choice.

Blood samples were gathered before and after each workout, plus the women's mood and anxiety levels were assessed both 10 and 30 minutes after the end of each session. It was found that while both sessions resulted in a temporary mood boost, the prescribed-intensity workout had a stronger and longer-lasting effect.

Additionally, only that session resulted in a rise of endocannabinoid levels in the bloodstream. Endocannabinoids are cannabinoid molecules which occur naturally in the body, and it has previously been suggested that they may help lower pain and depression by strengthening connections within the brain. They could also assist in reducing intestinal inflammation, and treating obesity.

The inferior effect of the self-moderated stationary bike sessions was likely due to the fact that participants tended to "take it easy," not getting as vigorous of a workout. That said, it could also be a psychosomatic effect, as the participants believed that a pace set by another, more authoritative person would be more conducive to relieving depression ... so their minds and bodies made that happen.

In either case, the results mesh with the findings of one of Meyer's previous studies, in which it was determined that depressed women who performed prescribed workouts subsequently had higher levels of brain-derived neurotrophic factor (BDNF) – this is a protein that regulates neuron growth, and depressed people tend to have lower levels of it in their blood.

"Finding alternatives to medication is important for the treatment of depression," says Meyer. "If we can figure out how exercise works with the endocannabinoid system, we could then design optimal exercise interventions."

A paper on the research – which also involved scientists from the University of Wisconsin-Madison, Medical College of Wisconsin and William S. Middleton Memorial Veterans Hospital – was recently published in the journal Medicine & Science in Sports & Exercise.