Can Regular Exercise Improve Mood and Ease Anxiety?

Maybe Not, Scientists Say, If You Are a Laboratory Rat

In a recent addition to the otherwise soothing body of scientific research on the beneficial effects of regular exercise on anxiety, researchers at the Central Institute of Mental Health at the University of Heidelberg in Mannheim, Germany report recent experiments involving rodents that suggest exercise may actually increase anxiety rather than relieving it.

 

When mice have running wheels in their cages, they typically spend nearly every waking minute exercising. A lab rat may run 12 km (7 miles) every day. Exhausted, the little rodents quickly fall asleep at night and no researcher has ever observed nightmares or insomnia in a rat that has access to an exercise wheel in its cage.

Take away the exercise wheel, the German researchers tell us, and a surprising picture emerges.

When the University of Heidelberg research team removed the exercise wheels from their lab rats' cages, the animals began to behave as if they were, well, in a cage they could not escape. The animals froze in place or fled to dark corners of their cages, as if they were experiencing extreme anxiety. The more the rat had used the exercise wheel before it was taken away, the greater the change in its behavior.

Too much exercise seems to make animals a nervous wreck.

These findings fly in the face of numerous previous studies that have investigated the role of exercise in regulating the production of brain chemicals that affect mood, especially serotonin, dopamine, and norepinephrine. The German researchers chose to focus on the effects of exercise on the structure of the brain itself, particularly the hippocampus.

In rats, in humans, and in other animals, the hippocampus is part of the limbic system. Straddling the dividing line between left brain and right brain, this area of the brain is responsible for processing recent memories, inhibiting harmful behaviors, and making distinctions between left and right, forward and backward, and up and down.

Damage to the hippocampus, in rats, in humans, and in other animals, results in excessive activity. In a rat, this may be constant exercise. In a human being, this may be a tremor that begins on one side of the body. Rats and humans alike suffer short-term memory loss after hippocampal tissue is destroyed by disease, injury, or toxic exposure. Exercise, however, helps new brain connections grow.

Certain neurons in the hippocampus known as place cells are activated by movement through the environment. When a rat is resting, these neurons hardly fire at all. When a rat moves through the same space in its environment, these cells may fire up to 40 times a second. Repetitive exercise causes massive activity in this one area of the rat's brain.

But is brain growth necessarily a good thing? The researchers in Heidelberg observed changes in the hippocampus that seem to correlate to "overloading circuits" in the hippocampus when laboratory rats exercise all the time. When the hippocampus is injured, then rats cannot interpret their environment, and freeze in place, or they cannot sort out appropriate ways to respond to their environment, and hide in corners. All of this happens despite the fact their brains have grown new connections to the hippocampus while the animal was on the exercise wheel. Would this also happen to someone who spends half a day every day on a treadmill or elliptical trainer?

Laboratory Studies of Rodents Don't Always Generalize to Humans

The results of this experiment seem to contradict decades of research, so Dr. Peter Gass and Dr. Johannes Fuss, authors of the study, offer alternative explanations of the results. Rats, they remind their readers, do not necessarily experience anxiety the same way that humans do.

In a human being, finding a dark corner and hiding is usually a counterproductive behavior. In a rat, especially a rat living in a laboratory in which the investigator also keeps a pet cat, finding a dark corner and hiding may be an essential life skill. The changes to the hippocampus that seem to increase behaviors associated with "anxiety" may actually be beneficial to lab rats. They just would not be beneficial to humans.

Is there any evidence that exercise can increase anxiety in human beings, rather than reducing it?

There is unequivocal evidence that exercise reduces anxiety in humans who have a chronic health condition. In a statistical analysis of 40 clinical trials, University of Georgia at Athens researchers publishing their findings in the Archives of Internal Medicine calculated that exercise lowered anxiety and there was very high level of confidence the results of these studies were not due to chance, that is that 40 studies were not a fluke. Exercise programs for the chronically unwell lowered anxiety when:

• The participant in the exercise program had previously been sedentary,
• The state of anxiety had existed for more than a week,
• The exercise period was greater than 30 minutes, and
• The exercise program was conducted for at least 12 weeks.

The 20 to 40 per cent of regular exercises who are "addicted" to exercise, however, tend to suffer anxiety and depression on days they are unable to work out. People who are addicted to exercise tend to exhibit:

• Feelings of euphoria after completing a session (for example, the "runner's high"),
• A need to keep increasing the length of their exercise sessions to get the same emotional benefit,
• Difficulties in meeting personal, social, or professional obligations due to the amount of time spent working out, and
• Anxiety, depression, and poor judgment when unable to exercise.

This negative addiction to exercise is slightly more common in women than in men. Men who think of themselves as physically fit benefit from many cultural cues that suggest they are in charge, in control, and valuable people. These cultural cues are not as abundant for women.

And what about people who work out occasionally? At least in Finland, getting exercise 2 or 3 times a week seems to enhance emotional health. A study of 1,547 Finnish men and 1,856 Finnish women found that those who participated in 2 or 3 sessions of mild to moderate exercise every week experienced less anger, less anxiety, and less depression than those never exercised at all.