Creatine

Creatine is a substance found naturally in muscle cells. It helps your muscles produce energy during heavy lifting or high intensity exercise.
Creatine gives your muscles more energy and leads to changes in cell function that increase muscle growth.
Supplementing with creatine can result in significant increases in muscle mass. This applies to both untrained individuals and elite athletes.
Creatine is one of the best supplements for improving strength and high intensity exercise performance. It works by increasing your capacity to produce ATP energy.