The Importance of Repetition
The value of a workout is only as good as the integrity of each individual repetition performed in that workout. If an athlete was doing 3 sets of 10 or just 1 set to failure the quantity of muscular growth will be in direct relationship with the quality of with repetition.
It has been found that slower repetitions "produce more muscle tension and greater muscle force." A major reason for this is the fact that faster repetition speeds create momentum, which allow the athlete to use heavier resistance but it in fact reduces the tension on the working muscles, not to mention this practice is quite unsafe.
Studies have shown that athletes using a slow and controlled repetition speed have gained more strength than those who employ a standard repetition speed. By standard repetition speed we mean a repetition that greatly ignores the eccentric, or lowering phase of the movement. The athlete who lifts with a standard repetition will push hard on the chest press, for example, but will let the weight drop rapidly as to not fatigue them for another push.
The slow and controlled repetition will honor the fact that the muscle works in two directions. Fact: The muscle is 40% stronger during the eccentric phase [or lowing phase also referred to as a negative phase.] This is illustrated in the fact that after an athlete can no longer push up a resistance in the chest press, for example, he is still able to hold the weight and even lower it slowly! The most efficient way to train the entire, whole, every single fast and slow twitch fiber is to work the muscle both ways. How can we work the muscle both ways? Slowly.
Kelso, Tom. "The Basics of Muscle Contraction: Implications for Strength Training." Maximize Your Training: Insights from Leading Strength and Fitness Professionals. Edited by Matt Brzycki. © 2000
Wescott, Wayne L. Ph.D, Tracy D'Arpine. High-Intensity Strength Training. © 2003 Healthy Learning.