Michigan State University study showed that students who went to gym, or did frequently exercises (yoga, TRX, kettlebell etc.) helped more to get higher grades than those who spent more time in library or study hall. 

The study, led by Pivarnik and MSU doctoral student Samantha Danbert in the Department of Kinesiology. He said the following:

We found that these students' cumulative GPAs were 0.13 points higher. Although this number may not appear to be significant, in the end, that amount could mean the difference to those students on the cusp of getting into graduate school or even advancing to the next academic year.

Pivarnik noted that 74 percent of those with memberships successfully gained their sophomore status while only 60 percent reached that goal in the nonmember group.

The good question is in this phenomenon is the Why? Why sports helped to get better results with less study?

The following effects could caused this phenomena:

running1. Doing exercises helps to lower the stress factor, it is the best antidepressant

2. Helps to connect the dots, as sleeping so doing exercises helps the brain to have some rest, it needs not so many brain work. When you are in a state of rest, the brain have time to connect the dots

3. More endorphins in the body, compared to learning (doing brain work) it is a completely different form of experience, it helps to keep you confident even in longer term

4. While you are doing body work, the mind is not working as badly as during learning, which breaks the walls of your barriers. The less barriers you have, the more you are able to experience.