Part of staying in shape is mental, but you've probably never thought about this when it comes to your workouts.

A new study shows that the color green may be best when it comes to maximizing your workouts. Why? Studies show it connects your brain with the positive feelings that come with exercising outside.

Here's what researchers at the University of Essex in England did:

Several men rode a stationary bicycle indoors while watching a video that made it seem like they were cycling outdoors.

A filter on the video was switched from green, to black and white, and then to red.

The subjects reported feeling less fatigued, and said they experienced fewer mood swings when they watched the green version of the video compared to the other filters.

So going green isn't just for the environment anymore!