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Building muscle is a numbers game. Thankfully, you don’t need a degree in exercise science to excel at this game, just a basic understanding of a branch of arithmetic known as meathead math. At the heart of meathead math – the figure that determines much of what we do when we lift – is the repetition, or the rep.

When you curl or press or pull a dumbbell, that single action is one repetition. A group of reps is called a set. Three sets of 10 is the most common lifting protocol, for reasons no one can really explain. It seems back in the late 1940s, an army doctor did some weight training experiments using the 3 x 10 scheme and, from then on, the industry as a whole took this formula as gospel.

Now there’s nothing wrong with following this plan, beginners especially will benefit from its simplicity. That said, different muscle groups have different functions and abilities; training the entire body with a generic, one-size-fits-all approach will limit your development and bore you to tears. A better way exists! But before we get to that, let’s take a step back and talk about the thing every gym goer is pursuing – muscle.

What is muscle?

Muscle is a cellular tissue that produces movement in the body through a series of contractions. Each muscle is made up of thousands upon thousands of tiny fibres, and within those fibres are even more tiny fibrils. These muscle fibres are controlled by nerves. When those nerves channel an impulse from the brain, the muscle contracts and movement is produced.

Skeletal muscle fibres come in two main types: slow twitch (type I) and fast twitch (type IIa and IIb). The names of these fibres tell us much about their functions. Slow twitch fibres produce less intense contractions and have great endurance, whereas fast twitch fibres produce powerful contractions but gas out quickly.

Our genetics and the specific jobs of the muscles in question determine their overall fibril composition, although most muscles are a balanced mix of both fibre types. This fact alone illustrates why firing off three sets of 10 every time you’re in the gym isn’t the best plan of attack; if different muscle fibres do different things, shouldn’t you employ a variety of rep ranges and weights to ensure your training delivers the best results possible?

Yes. Yes you should.

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Training for strength versus training for size

Strength and size are often thought to be synonymous. And while the two traits are related, you can certainly have one without the other. There are plenty of powerlifters with relatively modest physiques, just as there are lots of bodybuilders who aren’t nearly as strong as their bulk would suggest.

Strength is a function of two main factors: the size and type of the muscles fibres being recruited during a lift and the efficiency of the nervous system during said recruitment. The faster those fibres fire, the greater the force produced. In order to train the nervous system to recruit the most fast twitch muscle fibres possible, you need to lift heavy weight for low reps, usually no more than five or six for every set. Remember, those fast twitch fibres produce a ton of force, but they get tired fast.

Training for size is a slightly different story. Mechanical tension (i.e., forcing your muscles to work) and metabolic stress (i.e., the cellular swelling that occurs when a muscle works to failure) are the factors that lead to hypertrophy (that’s gym-speak for muscle growth). Finding the proper balance between these two factors is the challenge in getting jacked. If the weight is too heavy, you won’t be able to perform enough reps to induce metabolic stress; if the weight is too light, you’ll be relying mostly on slow twitch fibres and won’t be able to produce enough mechanical tension. For gains in size, 8-15 reps for every set often does the trick.

Putting it all together

Gym rats and sports scientists have determined that to make real, appreciable progress in the weight room, you need to perform somewhere in the neighbourhood of 50-120 reps for every body part each week. Now that we know the weekly rep total we’re aiming for, we can apply some meathead math and come up with more precise numbers for each session.

If you perform three total body workouts each week, you’re looking at 15-40 reps for every body part each workout. If you’re in the gym four days a week, the rep range drops to 12-30 for every body part. Dividing those reps into multiple sets is important as it helps reduce excessive soreness and ensure you’re lifting with enough focused intensity.

For the best results, 80 per cent of your exercises should target the fast twitch fibres with multijoint movements such as squats and dumbbell presses with heavy weights in the 5-8 rep range. The remaining 20 per cent should focus on higher volume exercises such as arm curls and lateral raises for 10-15 reps. This will help to pack on some muscle mass while the lighter weights will give your nervous system a bit of a break.

Paul Landini is a personal trainer and health educator at the Toronto West End College Street YMCA. Follow him on Twitter @mrpaullandini.

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