University of Colorado Boulder scientists tried to find answers to this question in their recent research. Two sets of rats were studied, the first set would run when they wished and the other set was made to run on wheels that turned at regular intervals. The rotation of the motorised wheels was tuned such that the rats that were forced to run ran as much as the rats who ran on their own.
During six weeks of these voluntary and forced exercises, both the groups were tested daily for anxiety. Their anxiety levels were measured by how long they froze when they were subjected to a stressor. This is similar to the way a deer reacts when it suddenly sees headlights of a vehicle on the road. The longer they stay frozen, the higher the anxiety level.
"Regardless of whether the rats chose to run or were forced to run, they were protected against stress and anxiety," said Greenwood, lead author of the study. The sedentary rats froze for longer periods of time than any of the active rats.
"The implications are that humans who perceive exercise as being forced--perhaps including those who feel like they have to exercise for health reasons--are maybe still going to get the benefits in terms of reducing anxiety and depression", said the researchers.