If you've ever performed a resistance training workout, you're probably familiar with The Pump. Yup, I'm talking about that tightness and healthy swelling that occurs in your muscles after an intense training session. You know, the best time to look in the mirror and throw up a nice, double-bicep flex. So, this "pump" ... what causes it?

Repeated resistance training causes microscopic tears in muscle fibers. When you're done with a set or an entire workout and finally put down the weights, you release blood that has been backed up by muscle contractions and it is then rushed into the newly-torn muscle. The end result? Like Hanz and Franz famously say, you look pumped up.

Aside from the ego boost resistance training offers, it is also a great way to build lean muscle and burn fat. Providing your not lifting cupcakes and pizza slices at the same time, lifting weights will increase your resting metabolism, causing you to burn more calories while at rest and help to prevent against the storage of fat.