Rate of Perceived Exertion

by Eric Oliver, PT, USATF1

The rate of perceived exertion method (RPE) of gauging your body’s effort level during endurance exercise will help you to efficiently utilize the appropriate energy system and fuel source to power your endurance effort.

In order to take your training competence to the next level, it is important to understand the concepts explained on this page.

 

Quick Physiology

Where Does Your Body’s Fuel Come From

  • The energy that powers our muscles during exercise is called ATP (adenosine triphosphate).

  • ATP is created when various energy systems break down a fuel source.

  • These fuel sources are called substrates.

  • The key substrates used by an energy system to create ATP include: glucose, glycogen, and fatty acids

    • Glucose is a form of sugar found in the bloodstream.

    • Glycogen is a sugar stored in muscle tissue and the liver. It is converted to glucose before entering the bloodstream to be used as a fuel source.

    • Fatty acids are found in the bloodstream and are sourced from the body’s stored fat.

How Are Substrates Converted To Energy?

The two energy systems that create ATP (energy) are the anaerobic energy system and the aerobic energy system.

  • The anaerobic energy system can create ATP WITHOUT the presence of oxygen.

  • The aerobic energy system creates ATP WITH the presence and consumption of oxygen.

The Effort In Which You Exercise Determines The Energy System Being Utilized

In other words, as your heart rate increases your reliance on a particular energy system and the ratio in which you rely on them will change. Therefore, the harder your running effort, the higher your heart rate. The higher your heart rate, the more you shift from using your aerobic energy system to relying more on your anaerobic energy system. THIS IS AN IMPORTANT CONCEPT TO UNDERSTAND BECAUSE THE ANAEROBIC ENERGY SYSTEM CAN ONLY BE UTILIZED FOR SHORTER PERIODS OF TIME AS COMPARED TO THE AEROBIC ENERGY SYSTEM.

How Does This Relate To RPE?

Download the RPE Scale here.

As you can see with the RPE Scale, different RPE grades correlate to different efforts of running—

  • The harder you run, the higher your heart rate.

  • The higher your heart rate, the more you tap into your anaerobic energy system.

  • The more you tap into your anaerobic energy system, the shorter you will be able to maintain that given effort (pace) due to the limited capacity of the anaerobic energy system.

Therefore, by paying attention to your RPE you can ensure that you are utilizing the appropriate energy system for the duration and level of experience that you are training. The RPE chart allows you to subjectively grade the effort level to which you are exercising by correlating it with a couple of self-checks—breathing rate and ability to talk.

  • For someone who is new to running, we recommend that you stay in the RPE of 3 to 6. The higher the efforts, the harder your body has to work (cardiovascularly and muscularly), so if you are going to run at a higher RPE you need to make sure that your heart, skeleton, tendons, ligaments, and muscles are able to absorb the stress and strain.

  • For a runner who is more experienced and musculoskeletally developed, using the full range of RPE from 3 to 10 is appropriate so long as the workouts are programmed responsibly. Ie. Limit higher RPE workouts to once or twice per week and keep the total volume of running low relative to your RPE 3-5 run days.

How Does RPE Relate To Pace?

Training with RPE (ie. training by ‘feel’) allows you to listen to and train your physiology rather than holding firm to a set pace. Training “by feel” provides you with more flexibility to change your pace (faster or slower) depending on the conditions in which you are running—heat, cold, humidity, uphill, downhill, flat, elevation, hydration, sickness, blood sugar level, sleep, carbon shoe (yes, even this!), and any other extrinsic/intrinsic factor that will effect your running pace on any given day.

Training the appropriate energy systems (along with performing complimentary habits such as recovery, nutrition, hydration, strength training, etc) will allow your energy systems to become more efficient. Practically speaking, your RPE of 4 at a 9:00/mile pace will eventually improve to an 8:30/mile pace at the same RPE of 4 over time and stress adaptation, but only if you train the energy systems appropriately. This is the beauty of our body—place incremental stress on it, and it WILL adapt and become stronger and more efficient at whatever you’re practicing.

If you fail to pay attention to your effort level while running, you can misuse your energy system and musculoskeletal system. The results can include:

  • Suboptimal development of the energy systems necessary for your race (or race strategy). Ie. You don’t maximize the time spent training for the distance you are attempting to race

  • Plateauing of your performance from season to season

  • Bonking (“hitting the wall”) during long runs or during your race. Ie. You start your marathon at a RPE of 6 and blow through your energy stores because you used too much of your available substrates to fuel the anaerobic energy system)

Final Thoughts

Running a marathon, half-marathon, or ultramarathon is primarily performed utilizing the aerobic energy system, if done correctly.  In fact, 75- 85% of the ATP produced during these races should be done by the aerobic energy system.  If you start tapping into the anaerobic system too much or too soon in your race, you risk hindering your performance by burning through your glucose too quickly during the course of the race.

When you burn through your glucose too quickly it becomes difficult for your body to keep up with your muscle’s demand for ATP, because as you recall you need the glucose to create ATP.  When you no longer have enough ATP to power your body, you “hit the wall”.  Unfortunately, once you get to the last of your available glucose in the bloodstream it becomes difficult to replenish it.  Your body cannot convert glycogen quick enough to fuel the processes that create ATP before you get to the end of your race, even with ingesting carbs (gel packets, gummies, etc).  Also, you cannot just simply switch to using oxygen and your aerobic energy system when you start to get in trouble.  This is because glucose is still necessary for the aerobic system to use oxygen to create ATP.  Therefore,  if you are on the struggle bus in the back half of your long distance race due to hitting the wall, the fuel that you are ingesting will not be converted quickly enough to make up for the deficit you created. You will not be able to maintain your desired pace, and you will hit the wall forcing you to resort to running significantly slower or even walking just to make it to the finish. Also, salt tablets won’t do diddly squat for replenishing your lost glucose.

Long story short—if you don’t properly train your body to efficiently create and utilize ATP for extended periods of exercise and/or you don’t stick to running within the limits of your aerobic system you will sabotage your performance either in training or in your race.  Think of your body as a race car, all of the engineering, tuning, and aerodynamics won’t do the car any good during the race if you don’t have enough fuel to power it. Just as race car drivers plan out the use of their fuel when racing in order to optimize their performance, you too must do the same. Minding your RPE is an effective strategy to accomplishing this feat.