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How Many Reps Should I Do?
by Stephen Holt

Many people perform 12 reps of every exercise (except for abs which somehow “magically” deserve more reps - another fallacy) without ever questioning why. In order to optimize your results, you must understand this fact of physiology: Muscles don’t count reps! Muscles only know time under tension. Muscular tension beyond a certain threshold and maintained within a certain time frame causes the chemical reactions in the muscles that result in the body changes that you want.

Just like in the lab, the results of a chemical reaction that takes place for a short period are different from the results of a chemical reaction that takes place for a long period.

The tension and time are inversely proportional. You can maintain high tension for only a short amount of time. That ‘s why a 1-rep max, the most weight you can lift once and, therefore, the most tension you can generate (concentrically) in a muscle, is indeed only one rep.

For physiological (and, hence, chemical) reasons, you cannot maintain that same level of tension any longer.

On the other hand, if the tension is low as in aerobic exercise, you can perform for hours.

For general fitness gains (that is, a little more muscle, a little less fat, a little more strength), the typical muscle should be under tension for about 40-60 seconds to or close to fatigue.

Working backwards, we see that a 40-60 second set of 4-5 second reps comes to about 8-12 repetitions. This is where we get the traditional 8-12-rep set!

Unfortunately, many people are more focused on the “8-12” than on the “4-5” and race to finish the set as quickly as possible.

It is far more important AND productive to perform high quality repetitions than to simply “make it through” the set.

A productive set is a string of productive repetitions, not just a certain “magic number” of repetitions.

There is nothing special about the number 12!

On the other hand, there is a shortcoming with performing 12 s-l-o-w reps, also.

Your muscles contain a combination of endurance-oriented, fast recovering Type I fibers and power-oriented, more slowly recovering Type IIA and Type IIB fibers. The average muscle in the average person is about 50% Type I and 50% Type II.

An overly slow set of 12 or an overly long set of 20+ reps necessitates the use of Type I fibers only.

This means that you are ignoring at least half of your available muscle fibers if you are not working with high enough tension.

Moreover, it’s these underutilized Type II fibers that we tend to lose as we age, resulting in a drop in metabolism that leads to gains in fat mass.

In order to keep your metabolism high, you should perform your strength training sets within 40-60 seconds, in most cases. There are exceptions, of course, from person to person and from muscle to muscle.

For example, a world-class athlete in a speed or power sport such as Olympic lifting, 100 meter dash, high jump, etc. will have a higher percentage of Type II fibers when compared to an average person.

On the contrary, a marathoner will have a higher percentage of Type I fibers when compared to the average person.

Certain muscles, however, tend to be predominately Type I or Type II in most people.

Type II dominant muscles include the gastocnemius (the main calf muscle), the hamstrings, the triceps, and the rectus abdominis (one of the many problems with the way most people work their abs).

Type II dominant muscles respond best to high tension (heavy weight) and, necessarily, shorter time under tension (fewer reps.) Sets of 20-40 seconds (7-10 reps for most people with most exercises) to or almost to fatigue work best.

The major Type I dominant muscle is the soleus, the main muscle worked in seated calf raises. Type I dominant muscles need to be worked for 50-90 seconds.

People (okay – "men") who do fast, short sets of seated calf raises are actually training only the Type II fibers of a highly Type I dominant muscle; numerically speaking, they are working only about 20% of the available muscle fibers. Not very effective!

Don’t perform 12 reps for no reason.

Know what type of muscle you are working and the results you want.

Estimate the time under tension that you need for that particular muscle, then divide by the time of your average rep (typically, 3-5 seconds).

This will give you an individualized rep range based upon physiology and chemistry as opposed to gym lore and unfounded traditions.

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Stephen Holt Fitness Lutherville, MD 21093 410-453-6295