Repetition Speed: Why Slower Is Better

Repetition Speed: Why Slower Is Better

by Drew Baye

Slower repetition speeds are safer

When a material is exposed to a level of force exceeding its structural strength, it fails. In the case of the human body, this can mean pulled, strained or torn muscles and/or connective tissue, broken bones, or worse. The amount of force the body is exposed to during movement increases or decreases in direct proportion to the speed of movement. The faster you move, the more force the body is exposed to.

Even exercise using a relatively light resistance can produce injury if performed in a ballistic fashion.

A 230 grain .45 caliber bullet weighs less than half an ounce. A relatively light weight compared to the resistance one typically encounters during exercise. If I toss a .45 caliber bullet at your head from a distance of 10 feet, it might irritate you somewhat, but hardly cause any damage. If I throw the bullet at you as hard and fast as I can from that distance, it is going to sting, may leave a nasty bruise, and possibly draw blood. If I shoot you with a .45 caliber pistol from that distance, the bullet will punch a hole right though your head. In each instance, the weight of the bullet is the same. It is the speed at which it is moving and the amount of force produced that determines the level of damage.

Regardless of the efficiency or effectiveness of a particular activity for producing physical improvements, if the nature of that activity is such that its performance carries a significant risk of injury, it should not be performed for exercise. The purpose of exercise is to stimulate the body to produce physical improvements, not to cause injuries. A slow repetition speed is necessary to minimize the risk of injury during exercise.

Slower repetition speeds are more effective

By moving slowly and performing the turnarounds smoothly, it is possible to avoid meaningful increases in momentum which may reduce muscular loading during portions of an exercise. By maintaining a slow speed it is possible to maintain a relatively consistent level of momentum over the full range of movement, which loads the involved muscular structures more efficiently.

In 1985 Ellington Darden, Ph.D. supervised the training of 65 women between the ages of 19 and 64. Subjects performed high intensity strength training 3 times per week, for ten weeks, performing one set of 4-6 exercises for the lower body and 6-8 exercises for the upper body, using a 2 second positive and 4 second negative movement. The average strength gain in ten weeks was 30.4%, or 3.04% per week.

In the fall of 1986 and the summer of 1987, Dr. Darden supervised Similar groups of 49 women. Subjects followed the same program with two major changes. The study was performed in only six weeks, and each exercise was performed with SuperSlow protocol, a 10 second positive and 5 second negative movement. In six weeks the average strength increase was 28.94%, or 4.83% per week. A 59% greater increase in strength per week than the 2/4 group.

In a study by Wayne Westcott, Ph.D. comparing the 2/4 and 10/4 high intensity training protocols, the average increase in weight loads after 8 weeks was 22 pounds for the 2/4 group, and 27 pounds for the 10/4 group. In another study by Dr. Westcott comparing the 2/4 and 10/4 protocols where subjects were instructed by a trainer, the average increase in weightloads after 6 weeks was 12 pounds for the 2/4 group, and 22 pounds for the 10/4 group. This is a very significant increase in strength for such a short period of time.

If slower is better, why not perform one minute repetitions?

The slower a person moves, the poorer their perception of position and movement becomes. Most people have difficulty moving extremely slowly without the movement degenerating into segmentation (a series of short starts and stops) Rather than a continuous, uniform movement. While a slower movement speed may very well be more effective, very few people possess the level of motor control required to perform extremely slow (30/30 or slower) repetitions without segmentation.

Why 10/10?

Why not 8/4, or 12/6? Anything between a 6 and 14 second positive during most exercises is effective. For most exercises, a 6 or more second positive movement appears to be slow enough not to involve a significant degree of momentum, and 14 seconds appears not to be so slow that it becomes difficult to move smoothly.

A ten second positive movement is simply an average of the two, and an easy number to remember.

What about the fact that a particular repetition speed can result in considerably different actual movement speeds depending on the exercise, ranging from an angular velocity of over 20 degrees per second during the pullover to less than 10 degrees per second during the calve raise, (both depending on the subject's range of motion), and varying in compound movements depending on the subject's limb length? It may be appropriate to refer to repetition speed in terms of angular velocity for simple movements and, perhaps, inches per second for compound movements for research purposes where a high degree of accuracy is necessary. However, this is unnecessarily complicated for general purposes.

Even if repetition speed was commonly defined in this manner, it would only confuse matters more, since movement speed is not constant during exercise. Movement speed varies throughout the repetition, accelerating from 0 at the beginning of the movement to a particular maximal speed, then gradually decelerating to 0 again towards the end of the movement. The 10/10 guideline is sufficient for general exercise purposes. 10/10 is adequately slow to minimize force and acceleration even in relatively long movements such as the pullover.

Exceptions to 10/10: High-Friction Equipment

When using machines which possess a noticeable level of friction, a faster negative movement is required to avoid unloading. An example of why this is necessary would be pushing a heavy box up an inclined plane, verses controlling the descent of the same box down that plane. As you push the box up the plane, friction between the bottom surface of the box and the plane makes the box more difficult for you to move. As you control the speed at which the box slides down the plane, friction reduces the amount of force you must produce to slow its descent.

If you perform an exercise at a relatively fast speed, the resulting increase in momentum assists you during the positive movement, allowing you to lift an amount of weight that would be heavy enough to provide a meaningful level of resistance during the negative. If you perform an exercise slowly you will not be able to lift as much weight as you can at the faster speed. The lighter weight will feel much heavier during the positive, due to the lack of assistance from momentum, but if you perform the negative at the same speed, the weight will feel much too light. This is due to friction.

By moving too slowly during the negative, you allow the muscle a brief respite, unloading it somewhat. The negative should be performed slowly enough to minimize the amount of force the body is exposed to, but not so slowly that the muscle is allowed a rest. By not moving so slowly as to allow the muscle to rest, you are accentuating the negative. For most exercises a 4 to 6 second negative appears to be effective for this purpose.

If the level of friction in a machine is so high that it is impossible to perform a 10 second positive without the movement arm sticking, a faster positive and negative would be required to allow for a smooth and consistent speed of movement.