Five Is The Magic Number

What makes a repetition stimulating?

Perhaps you have already heard something like “effective repetitions”, “stimulating reps” or “junk reps”. They all refer to the fact that not every repetition of a set is equally efficient to stimulate muscle hypertrophy. To force a muscle to grow, certain key factors have to be met.

Muscle fibre activation has to be high. Your muscle consists of different fibre types that react differently to loading. Low threshold fibres are the first to kick in, but they are relatively weak. They help you move lighter loads, but as soon as they fatique, high threshold fibres start working to keep the light load moving. High threshold fibres are relatively slow to act but stronger than low threshold fibres. They are also activated almost immediately when the load is very high because the imposed stimulus is so high and low threshold fibres are too weak to move the weight alone.

The speed of the movement (bar speed) has to be relatively low. Muscle tension is a key factor for hypertrophy. To keep tension on your muscle, muscle fibres must shorten slowly and therefore bar speed has to be quite low (low in this context means “not explosive”). We know this because high-velocity movements like jumping involve very high levels of motor unit recruitment, but fail to trigger muscle growth.

If we look at the first two points, one might conclude that lifting very heavy weights is the most efficient way to grow muscle because high loads force high muscle fibre activation and a slow bar speed. But it seems that there is also a certain volume threshold you have to reach in a given training session to motivate your muscle to grow. Right now, we don’t know exactly what this volume threshold is, and it is probably highly individual, but it seems that 10-15 stimulating reps should do the trick.

Is this already stimulating?

So, how do you know if your reps are stimulating enough in practice? It seems that the last five reps of a set before you reach failure can be considered effective. For most people a 5 repetition maximum translates to about 85% of their 1 rep max, which is enough weight to force maximum muscle fibre activation with every repetition. When using lighter weights than a 5RM, the repetions before you reach those last 5 reps could be considered non-stimulating. Their only purpose is to create enough fatique that your high threshold muscle fibres are forced to work while you perform your last 5 reps before temporary muscle failure. Those lazy bastards!

Take a look at this great infographic by Strength and Conditioning Research for a nice overview. If you want to delve deeper into training volume and aren’t afraid of science, read this awesome blog post.

What is the takeaway?

What does all this mean for your training? No matter in what rep range you train, you have to train hard. If you’re doing a set of 20 leg presses and your last reps looks exactly like your first rep, you are doing it wrong! This won’t bring you close enough to failure to ellicit any stimulus, you’re only wasting your time with non-stimulating reps and stopping before you even reach the holy land of stimulating reps. Get your pain face out and make sure you put enough effort in your training!

If you like training with heavy (85%+) weights, make sure you hit your volume threshold of about 10-15 reps per training. This explains the popularity of set x rep regimes like 3×5, 5×3, 4×4, etc. Take into account that performing multiple sets of e.g. your true 5RM could be extremely hard or outright impossible to achieve as you might not be able to completely recover between sets! Make sure to compensate for this by doing more sets to reach your volume threshold.

Finally keep in mind that going to failure is quite taxing on your ability to recover. If you find that this is too much for you to handle, compensate the lacking effective reps by adding additional sets to your workout. Listen to your body and remember that you have to make your training sustainable to reap long term benefits!

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