Willpower is important to getting off the couch to exercise. The desire to work out may be related to the microbes in the gut. A research team has found a way to make rodents want to run. This group has set the stage for finding out if similar signals help keep humans active by revealing how these molecule talk to the brain.

A microbiologist at Harvard Medical School who is co-founder of Fit Biomics says that the work establishes how critical the microbiome is for exercise and that it provides a new gut-brainconnection. Kostic, who wasn't involved in the research, thinks that one day the microbes could be used to make pills.

A University of Pennsylvania microbiologist studied mice bred to have a lot of genetic and behavioral variation in order to understand why some people like to exercise and others don't. The difference in how far the mice ran on wheels in their cages was more than fivefold.

There were no significant differences in the genetics of the mice. The researchers noticed that mice treated with antibiotics were less active. The treatments affected the brains of the mice. The activity of certain brain genes declined, along with levels of dopamine, a neurotransmitter that has been linked to "runner's high."

When given some of the gut microbes from vigorous mice, germ-free mice became more active. The neurotransmitter builds up in the brain's reward center when a signal is sent by thosebacteria that interfere with anidase that breaks down dopamine in the brain.

By stimulating those nerves, the team was able to send that pro- exercise command to the mice.

In the lab, Thaiss and colleagues exposed the subsets of gutbacteria as well as the substances the microbes produce to the outside world. The dopamine levels in the brains of the mice that were given one set of the molecule surged as they exercised. The mice got a dopamine boost when a different bacterium gave them genes for making fatty acid amides.

The work is called a tour de force. A microbiologist at the California Institute of Technology says that a lot of different layers of discovery are not found in a single paper.

The finding will hold in people. Juleen said that she would be very cautious in extrapolating how the results are related to human physiology. Rodents have different muscle structures and activity patterns. Rodents don't make New Year's Resolutions.

Studies have shown that marathoners have high levels of a specific gut microbe. Dopamine plays a key role in motivating behavior. Kostic says that the reward system is such a central facet of the body that it is almost certainly true in other mammals.