Brie Larson shows off the muscles she gaining in nine months of training with a video of her pull-up abilities Julie Mazziotta is the Senior Sports Editor at PEOPLE, covering everything from the ...

Here's what actually happens when you "pull" a muscle. The human body has three types of muscles skeletal, cardiac and visceral. But we can only control, and damage, our skeletal muscles.

Your tricep muscles contract and pull, while your bicep muscles relax, causing your arm to straighten back out. You can find antagonistic pairs in your legs too. Just extend and curl and see which ...