Let’s start by defining a few terms:
RPE: Rating of Perceived Exertion. The RPE is a scale from 1-10 created by Gunnar Borg in 1970. It was originally created by Borg to prescribe endurance training intensity.
Volume: Total work performed. This can be measured by the total sets, the total reps or the total tonnage worked for a specific muscle group or exercise. Hypertrophy does increase as the number of sets you perform increases. It is believed that you get 60-70% of the stimulus from your first hard set and each subsequent set will provide less and less stimulus. Also, the higher volume will contribute to your overall systemic fatigue which will in turn affect your ability to recover and adapt. Volume is not a critical driver of hypertrophy, but if you do too much, you will build up too much fatigue and lose your ability to grow.
Frequency: Number of times you train a specific muscle group or exercise within a week.
Intensity: Load. This is the weight you are using in relation to your 1RM for that exercise. The closer you are to your 1RM, the higher the intensity. Intensity can also be expressed by the effort, or RPE, of the set. So, if you use a load close to your 5RM but only do 1 rep, the intensity is lower than if you do 5 reps, both at the same load. We use RPE to describe intensity. This gives us the ability to account for outside stresses. One day you may come in feeling great and use a load for 5 reps at an RPE of 7. The next time you come in after a poor night of sleep and a stressful day at work and use the same load for 5 reps but the RPE is now 9. The only difference is your preparedness for that training session. When you are prescribed an RPE for a given exercise, you evaluate your preparedness for that day alone. What you did last week doesn’t affect the weight you put on the bar today.
Using RPE to measure intensity will help manage your fatigue. Managing fatigue is critical in a progressive overload program. As the weeks progress in a cycle, your fatigue will begin to build. This is intentional and required for adaptation. Once we reach an overloaded state, we will return the program back to a fatigue reducing level which will allow your body to adapt, grow and prepare for the next ramp up to another overload. Using RPE to measure intensity will also prevent you from overdoing it when you are tired, and from underdoing it when your strength and energy levels are high.
Your strength will fluctuate from session to session based on your stress levels inside and outside of the gym. If you find yourself having a hard time hitting your RPE numbers in later sets of a given exercise and feel you need to lower the weight to keep the correct RPE - Do it. Lower the weight. It is more important to stay within our prescribed RPE range and maintain the volume that we ask for than it is to hit a specific weight. Your RPE should be your gauge, not the load you are lifting.