One of the most frequently asked questions when trying to write a program based off of percentages is, what percentage should I use for this certain amount of reps? Unfortunately there is no clear-cut right or wrong answer. The short answer is, it depends. It depends on your current level of training, your ability to recover, the volume you are working with, where you are in your training block, and many other factors. Thus, to ask such a question, expecting a black and white answer is impossible!

In this article we will introduce the topic of relative intensity (RI), and how it can be used to better answer the aforementioned question.


What do we really mean by intensity?

We need to distinguish between the two measures of intensity. We have both absolute intensity (AI) and RI, and both are useful for various measures of progress. AI, referred to by the strength community as simply just intensity, is pretty synonymous with weight. In other words, the heavier weight you use, the higher the AI.

The law of progressive overload states that with time, you must make progress in both volume and intensity in order to continue to make gains. That means that you must do MORE work, and that work must be of HIGHER difficulty. AI does a great job at being a good measure of progressive overload in a macro-cycle, or long-term measure. If a year ago you could only squat 225×10, and now a year later you can squat 315×10, you’ve increased the AI you can do 10 reps for by 90lb. Short-term progressive overload on the other hand, may be better measured using RI.

RI can be defined as the weight you are using for X amount of reps, relative to the maximum weight you can perform X amount of reps for. To give you an example, if you can do 225lb on the squat for an absolute max of 10 reps. Yet, you are training using 205lb for sets of 10, you are working at 205/225=91% RI. RI is a much better measure of workout difficulty than AI is. And here is why, if you do sets of singles at 91% RI, or triples at 91% RI, the difficulty, or RI, is the same for both, although the AI will be higher in the 91% singles.

Lets say your max is 100lb, here are the numbers:

91% RI for singles would be 91lb
91% RI for triples would be 100lb x 93% x 91% = 85lb since 93% is associated with a 3RM.

As we can see from these numbers, the AI is higher for the singles, yet the RI is the same. The fact that RI can equate for difficulty, rather than just weight makes it a useful tool for programming, especially when using undulating rep schemes because you can easily compare workout difficulty between sessions.

Now, I am not saying that doing sets of 10 at 90% RI feels the same than doing singles at 90% RI. Singles and sets of 10 are two very distinct skills. Remember, strength is specific! What I am saying, is that it is the same difficulty relative to your ability to perform at that rep amount.

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