Magical muscle numbers

Most forms of exercise are organised into sets and repetitions. Sets and repetitions are the fundamental building blocks of exercise, just as paragraphs, sentences and words are the building blocks of written language.

When you first start exercising with repetitive movements in the gym, you will most likely be advised to start off with the standard three sets of 10 repetitions, with light to moderate resistance. This protocol is a great one-size-fits-all solution for novice gym goers, whatever their goal.

However, just as you will soon need to buy new clothes that are just the right fit for your fabulous new body, similarly your workout will also need streamlining to better fit your ultimate health, performance, and body sculpting needs.

So the burning question becomes, how many repetitions should you be performing?

“Low reps build power and size, high reps tone you up.” Hands up if you’ve heard this before. I have, many times, and find it more cringeworthy than an episode of The Office. This statement betrays more myths than the legends of Ancient Greece.

Let’s see what different repetition ranges actually do, how they work, and how we can best exploit them.

If we understand how the muscles work and respond to training, the explanation will be a lot clearer. Muscles are made up of little strands of proteins called actin and myosin filaments. These strands slide against each other, producing functional movement.

Many of these strands arranged in parallel combine to form myofibrils. In turn, many myofibrils arranged in parallel combine to form one muscle fibre (also known as a muscle cell).

Each fibre therefore contains myofibrils to produce movement, and a gel called sarcoplasm that stores energy and nutrients to power the myofibrils.

For the purpose of this explanation, think of a flexible rubber tube full of water, with rubber bands stretched through the middle of it from one end to the other. The muscle cell is the rubber tube, the water is the sarcoplasm, and the myofibrils are the elastic bands.

In short, when we resistance train, our muscles essentially adapt by forming new myofibrils (rubber bands), and storing more water and fuel inside the sarcoplasm (water), with the combined effect of increasing the size of each muscle fibre (rubber tube). This is how muscle growth occurs.

When more myofibrils (elastic bands) are formed, we call it “myofibrillar hypertrophy”, and when more water and fuel are stored in the sarcoplasm we call it “sarcoplasmic hypertrophy”.

Muscle fibres are arranged in bundles called motor units. Therefore, each motor unit consists of a bundle of fibres and a single motor neuron. The motor neuron passes an electrical signal from the central nervous system, causing the bundle of fibre to contract in unison. Many motor units combine to form each single muscle.

When you flex your biceps, your brain sends signals through your central nervous system to as many motor units in your biceps muscle as it can, causing all to fire at once.

Armed with the simple rubber tube analogy, we can see exactly how different repetition ranges will affect our muscles.

Performing low repetitions with high resistance is essentially what a weightlifter or powerlifter does. Very heavy weights are lifted very few times.

This conditions the muscles to handle heavy loads, resulting predominantly in myofibrillar hypertrophy (more elastic bands). It also conditions our central nervous system to fire more available motor units at any one instant.

Before myofibrillar hypertrophy even occurs, we can greatly improve our strength from central nervous system conditioning alone, which explains why some people are much stronger than they look. Therefore, performing sets of one to five repetitions will lead to great strength, but contrary to popular myths, not significant muscle growth.

Any bodybuilder will tell you that optimum muscular growth occurs when we perform sets of between eight to 12 repetitions with a moderate to heavy resistance. This is true because forcing a muscle to lift the heaviest possible weight it can handle for between eight to 12 repetitions results in both myofibrillar and sarcoplasmic hypertrophy (more rubber bands and more water in the rubber tube).

The motor units that are initially recruited by the central nervous system at the beginning of the set, quickly tire, and must be replaced by others. By the end of the set, a maximum number of motor units will have been recruited, meaning most of the muscle is stimulated.

Because the set is both moderately heavy, and long in duration, the muscle needs to become functionally stronger by both increasing its number of myofibrils (myofibrillar hypertrophy) as well as its capacity to store fuel (sarcoplasmic hypertrophy). So it is actually higher repetitions that lead to muscle growth, not lower.

‘Toning’ up is achieved by training for strength, muscular growth, or both, besides diet and cardiovascular exercise to reduce body fat.

‘Power’ is widely defined as the combination of strength and speed, so training for power involves a combination of low rep/high resistance strength training, combined with any form of speed or plyometrics training, but that’s another story altogether.

So here’s a more accurate answer to the repetition-range debate than even David Brent could quote without making anyone cringe: “Low reps with heavy weight build strength, higher reps with moderate-to-heavy weight build size, and adding in cardiovascular exercise and a calorie-reduced diet tones you up.”

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