Tools & Calculators

Rating of Perceived Exertion

RPE Explained

Throughout the First 42K program, you’ll notice we refer to RPE during your running workouts.

Understanding what intensity to exercise is important because it can tell you whether you are working too hard or not working hard enough. To do this the First 42K program uses a Rating of Perceived Exertion (RPE).

What is Perceived Exertion?

Perceived exertion is how hard you feel your body is working based on physical sensations experienced during exercise. When you’re running your heart beats faster, your breathing becomes faster and deeper, you work up a sweat, and your muscles begin to fatigue. These feelings are not objective like they would be if you actually measured your heart rate, for example. However, they can give you an estimate of your heart rate and your exercise intensity zone without the need for any measuring equipment.

How do you gauge your RPE?

To rate your perceived exertion, don’t focus on just one sensation. Instead, assess multiple sensations like your breathing pattern, amount of sweat, and level of fatigue to get a general sense of how hard you are exercising. Use your feelings of exertion rather than measures such as speed while running or comparing yourself to someone else. Then assign your exertion a number from 1 to 10 (see table below).

In the First 42K Program, we use the modified RPE scale with its 0–10 numbering as it is measured by an individual’s breath — from deep breathing to shortened breaths — making it easier to assess your level of exertion and calculate your estimated heart rate.

Calculate your 1RM

In the First42K program, you’ll notice we use % of your one-rep max (1RM) as your guide for what you should be lifting.

Your one-rep max is the maximum amount of weight you can possibly lift for one repetition.

Use this calculator to work out your 1RM.

Determining your 1RM can be done directly through trial and error and simply requires you to complete one full repetition with the maximum weight.

However, testing your 1RM can be a pretty intense operation, and it requires a high degree of caution to avoid injury.

Fortunately, you can also estimate your 1RM without testing it, using this calculator.

There are several common formulas used to estimate 1RM using the submaximal method. This calculator is powered by the Brzycki formula devised by Matt Brzycki which is fairly accurate for most people to determine an estimate for each movement.

Let’s say you know you can back squat 50 kilograms for 10 reps — and only 10 reps — with good form.

Based on that we can estimate not just your one-rep max (100% of your 1RM), but other loads as well: your 85% 1RM, 70% 1RM, or 50% 1RM, depending on what your program calls for.

The calculator estimates your one-rep max based on the amount of weight you can lift in a given move, and the number of clean reps you can achieve before muscle failure.

Try it for the back squat, assuming you can do 50 kilograms for 10 reps. Put 50 into the Weight Lifted field above and then select 10 from the Reps Completed. It’ll show your estimated 1RM to be 67 kilograms and your 80% 1RM to be 54 kilograms.

1RM Calculator