The number of reps in your workout has a significant effect on the effectiveness of your workout. However, it seems every guy lounging around the gym has a different strategy or opinion on what workout strategy is the best. Perhaps somewhat surprisingly, evidence shows that a lower number of reps per set is a more effective method of generating muscle growth, when properly done. High reps at comfortable weights will only stimulate muscle endurance. Also, prolonged repetitive workouts lead to an overload of lactic acid, a muscular by product (it’s what causes the burning sensation when you run too fast, too far) which hinder energy transfer.
The ideal rep range for developing muscle in most cases is between 5 to 7 reps. at a weight at which you have difficulty completing the 7th. Once it becomes easy to manage 7 reps in a particular exercise, it is time to increase the weight. In other words, it’s not about increasing the number of reps as your workout program progresses, it’s about increasing the weights while staying within the familiar 5 to 7 rep range.
The main advantage of a low rep set is that you are going into each set with a maximum of your strength and concentration, lifting the heaviest weights you possibly can. Therefore, you are not wasting energy by lifting low levels of weights once most of your energy and focus has been exhausted. There is a biological rationale as well, due to the two main types of muscle fibers found in the human body, slow twitch muscle fibers and fast twitch muscle fibers. While the slow twitch fibers have a great deal of endurance, they do not grow much. Fast twitch fibers are primarily used for quick movement and have high growth potential. These are the fibers that most readily respond to the chemical signals that more strength is needed in a given muscle group, stimulating growth. However, for muscle groups made up mostly of slow twitch fibers, like the forearms and the calves, it is best to do sets with higher reps, such as in the 10 or 12 rep range.
Therefore, in summery, stick to a low rep range for muscle groups like the chest, lats, biceps, triceps, shoulders and thighs, because of the concentration of fast-twitch muscle fibers there. For muscle groups like the calves, abs, forearms and upper traps, maintain a 10 to 12 rep range.