Being fit is not about building huge muscles. Unfortunately that is what everyone assumes and so when you go to the gym you find most people lifting weights so that they can build muscles. The most important thing when it comes to sports is having a strong body. Body strength is not only a function for the muscles but your motor system and there are several methods to increase your body’s strength.
Lifting heavy (> 90% 1RM) will improve strength by recruiting what are called high-threshold motor units. The muscle fibers associated with these motor units have the most potential for increasing strength.