Do you train your sets to the limit, or do you keep a few repetitions ‘in the tank’? In the first case, we speak of training to muscle failure; in the second, of Reps In Reserve (RIR). So how can you accurately estimate your RIR?

MUSCLE FAILURE YES OR NO

Whether or not to train to muscle failure is still a subject of debate among renowned bodybuilding coaches. Yet, it doesn’t have to be that difficult.

If you train with a low volume —let’s say 5 to 10 sets per muscle group per week—you can safely train your sets to the bitter end. Due to the low training volume, your body gets sufficient rest. Reaching muscle failure in itself probably does nothing extra for muscle growth; it is purely about the extra repetitions you create.

With a higher training volume, somewhere between 10 and 20 sets per week, it is best to train your sets with a few RIR. This allows you to perform more effective repetitions overall and therefore achieve more muscle growth. But rest assured, muscle growth isn’t going anywhere. If you train at high intensity and low volume, you will still reach your goal, just possibly a little slower.

It is common to train closer to muscle failure with isolation exercises than with compound exercises.

ESTIMATE RIR

It is not easy to accurately estimate the desired number of RIR. This certainly requires some training experience. As a beginner, feel free to train a few sets to muscle failure so that you get a feel for it. The point of actually training to muscle failure—that is, until you really can’t do another decent rep—is often further away than people think.

Additionally, there is a handy rule of thumb from coach Ryan Solomon: once your rep speed noticeably slows, you likely have around 3–4 reps in reserve.