The middle school years can be rough on kids. School gets harder, schedules get busier, and kids get tougher on each other than ever. Add to this a mix of fluctuating body chemistry and it's no wonder that many kids this age start to feel the first signs of depression. Want to help your middle schooler ward off these blues? Experts say a healthy, active lifestyle is a good start.

In a new study, researchers at the University of North Texas gauged the fitness of more than 400 sixth-graders based on a timed shuttle run drill as well as other tests of strength and endurance. The idea was to measure an overall fitness level for each child, rather than simply a cardiovascular fitness level (say, running a timed mile,) which could fluctuate drastically depending upon what else is going on in the child's life. Using these tests, researchers found that the more fit a child was in the sixth grade, the less likely she was to develop the symptoms of depression in the seventh grade.

The study found the strongest statistical link between depression and fitness was found in girls. Boys also showed a correlation, but it was far less pronounced. Researchers think that the overall lower level of depression in boys may have made it difficult to tease out a link.

This study did not try to understand why there would be a connection between fitness and depression, but researchers surmise that it might actually be a number of factors at play - physical activity can improve self-esteem, increase energy levels, and give girls the opportunity to receive positive reinforcement. Exercise also tends to stabilize hormones and boost the chemicals in the body - endorphins - that fend off depression.

It's just good stuff. And during the middle school years, kids need all of the good stuff they can get.

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