You’ve undoubtedly tried different programs in search of more size and deeper cuts. You’ve gone high rep, you’ve gone low rep, you’ve pyramided up, you’ve pyramided down hell, you’d do the freakin’ Hokey Pokey every day if some study somewhere proved that it packed on muscle.

One overlooked variable for many bodybuilders, however, is rep speed. The prevailing mantra is slow and steady, contracting the working muscle as forcefully as possible at the apex of each rep. Good advice, yes … but you can do better. In fact, by using the full spectrum of rep speed, from slow to fast, in your overall program, you can maximize your growth. Isn’t that really what it’s all about?

The Fast & The Furious

The speed of each rep you perform depends on the weight being lifted, the number of reps being performed and the level of fatigue of the muscle being trained. Usually, most reps are done in a slow and controlled manner, about one to two seconds for the positive and one to two seconds for the negative. Of course, as you go heavier and the muscle fatigue intensifies, the positive portion of the rep takes longer and the negative part of the rep accelerates. Generally speaking, typical speed is about three to four seconds per rep.

Training with reps that are faster than the typical three to four seconds can be beneficial for a number of reasons.

Explosive Reps

When you perform the positive portion of your reps explosively taking less than one second to complete them your fast-twitch muscle fibers are called into action to a greater degree. Fast-twitch muscle fibers produce the greatest muscle force (i.e., strength) and have the highest potential for growth.

The other major type of fibers found within your muscles slow-twitch fibers produce less force and are smaller than the fast-twitch fibers, but they have greater endurance capacity.

Targeting The Muscles

Fast reps may focus the workload more on the intended muscles. Some research suggests that fast-rep training relies more on the major muscle groups performing a particular exercise and less on the assistance muscles that help. For example, one study found that doing biceps curls with a fast rep speed predominantly used the biceps brachii muscle, as opposed to the brachialis muscle that normally assists in a biceps curl. Slower rep training, however, placed greater stress on the brachialis muscle and a little less on the biceps brachii. Although little research has been done in this area, it’s reasonable to assume that this holds true for other exercises besides biceps curls.

Power Of Speed

Training at a fast rep speed increases the pace at which your muscles can move a given weight. The faster you can move a given weight, the more power you have. Power is important for overall muscle strength because it helps you accelerate a weight, so increasing power will successfully increase your strength. Research shows that the best way to train with high reps is to pick a weight that is about 50% of your one-rep max or a weight that you can lift for 25-30 reps. The trick is to do only three to five reps with that weight for each set. This may seem too easy to do any good, but it’s necessary to prevent fatigue. Doing too many reps when training with fast reps will only compromise your speed and can lead to injury if your form breaks. Perform each rep with explosive power, completing the positive portion as fast as possible. Return the weight to the start position in a slow and controlled manner.

Slow Down

Just as fast-rep training has its advantages, training with slow reps can also offer benefits. Slow-rep training reduces momentum and forces the muscle to do more of the actual work. This can improve your overall strength and muscular size. Both slow- and fast-twitch muscle fibers are recruited, imparting gains on both. At the start of a slow-rep set, slow-twitch muscle fibers are predominantly used. As fatigue sets in, more fast-twitch fibers are called in for support.

Time Under Tension

Depending on how slow your reps go and how many reps you do, some sets can last up to three minutes, extending the time the muscle is under tension. This will fatigue the muscle far beyond anything you are used to. Muscle fatigue is important for stimulating size adaptations, increasing growth hormone and IGF-I (growth factor) levels.