Senior author Kenneth Walsh said skeletal muscle consists of two types of fibers -- running increases the amount of type I muscle fibers, while weight lifting increases type II muscle fibers.

The findings, published in the journal Cell Metabolism, found weight-bearing exercise, in addition to endurance training, may benefit overweight people.

The researchers genetically engineered a mouse, MyoMouse, to grow type II fibers by activating the muscle growth-regulating gene Akt1. The MyoMouse was stronger and faster than a regular mouse but didn't run with as much endurance on a treadmill.

Then Akt1 gene was turned off and the MyoMice were fed a high fat/high sugar diet with a similar caloric composition as a fast food meal. Over an eight-week period, the mice became obese, insulin resistant and developed fatty acid deposits in their liver.

The researchers then activated the Akt1 gene which led to the growth of type II muscle fibers resulting in an overall reduction in body mass and mice became metabolically normal.

"Type II muscle just doesn't allow you to pick up heavy objects, it is also important in controlling whole body metabolism," Walsh said in a statement.