Q: I've been bodybuilding for four years and I'm still not sure how fast or slow I should perform my repetitions. I often read that the reps should be slow, controlled and steady, only to turn the page to find another pro who says the reps should be fast and explosive. Who's right, who's wrong, and why?
A: Both are right. The speed, smoothness, consistency and control of reps vary according to the exercise, its purpose, the bodypart and the ordinal position of the set in your workout.
Repetition speed will vary, depending upon whether the exercise is performed with cables, free weights or a machine. Since resistance with cables is consistent over the entire range of motion, the most effective use of cables is by means of slower repetitions, with a pace that is consistent through both the contraction and extension phases.
With free weights, the moment of force, or resistance, varies through the arc of the movement: At some points, the weight feels heavier than at others, just the opposite of the sensation associated with cables. You have to apply more power at those higher resistance points than at others, which means you have to accelerate or decelerate your repetition. Free weights are thus more effectively employed by repetitions that are controlled but slightly more explosive.
Machines are a good middle ground between cables and free weights. They do not allow as precise an isolation as cable movements, but they do provide consistent resistance over the entire range of motion. Repetitions that are slow and controlled during the extension and explosive during the contraction are most effective when using machines.
THE PURPOSE OF THE EXERCISE
Speed of repetitions is also governed by whether the exercise you are using is for defining and shaping an isolated muscle, or whether it is for building overall mass of the muscle group. If the former, your repetitions should be slightly slower, smoother, more consistent and more controlled. If the latter, they should be more explosive and, perhaps, faster.
Smaller bodyparts require more isolated control than do larger bodyparts, so repetitions for the appropriate exercises are usually slower and more consistent. However, there are times when you want to build an intense burn in a muscle and for that you should pump your reps relatively fast. For big bodyparts, such as chest, back and quads, you'll be using much more weight, so your reps will naturally be slower.
THE ORDINAL POSITION OF THE SET
The speed of your reps will differ, dependent upon whether you are doing your warm-up set, your first working set or your heaviest set. Control your reps and keep them slow at the start of your warm-up set, but then increase the pace to work out the stiffness of the muscle group and pump it full of blood. Your first working set should be controlled and consistent, but at a slower pace, and your final heaviest set should be the slowest of all.