One of the key factors behind getting maximum growth stimulation from each exercise is the form in which you lift and lower the resistance. Form has profound but paradoxical influence on your response to the exercise. In effect, poor form is associated with a higher rate of performance improvement but a lower rate of strength gain. That is, by training in a fast, momentum-assisted manner you can lift heavier weights. But because more momentum means less muscle tension, the performance increases are much greater than the strength increases.
Poor form also brings into action assisting muscle groups to initiate the lifting movements. For example, let?s suppose you can cheat curl a 150-pound barbell by bending forward and using your hip and lower back muscles to start the resistance moving upward. Unfortunately, your biceps muscles are only partially involved in this cheating-styled movement. Once your trunk extensors overcome the barbell?s weight, momentum plays the major role in lifting the resistance.
On the other hand, slow, smooth training form facilitates muscle isolation and intensity. Slow movements also reduce momentum and, as a result, less weight can be lifted. But the targeted muscle groups are fully responsible for lifting and lowering the weight. Thus, greater growth stimulation is produced.
For example, let?s suppose that by using very strict and slow form in the barbell curl, you are able to lift only 100 pounds. You are not able to bring into action your hip and lower back muscles, but greater intensity is placed on your biceps muscles ? which is good.
Competitive weightlifters (both power lifters and Olympic lifters) must use momentum in the practice and performance of their sport. It?s a necessary part of their skill development. But, for the development of muscular size, which is the crux of bodybuilding, it is most effectively and efficiently accomplished by the performance of strict, slow, smooth lifting and lowering movements.