Using Rate of Perceived Exertion To Pace Your Distance Runs
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 utilize the appropriate energy system to power your endurance effort.
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. This system has a shorter duration during which it can create energy. There are two types of anaerobic pathways—one in which lactate is produced as a byproduct (lactic anaerobic), and the other in which no lactate is produced (alactic anaerobic). The alactic anaerobic system produces energy for explosive movements and sprints. It can only supply energy for this type of work effort for 10-15 seconds. The lactic anaerobic system is utilized for intense work efforts that can last up to 2 minutes.
The aerobic energy system creates ATP WITH the presence and consumption of oxygen. This system can create energy for an indefinite period of time. If you are sitting while reading this, you are using your aerobic system. You also will use your aerobic system during non-explosive and less intense forms of exercise.
The Effort In Which You Exercise Determines The Energy System Being Utilized
The reliance on a particular energy system is dependent on the effort of your activity. In other words, once your running effort reaches a certain threshold, the more you start to rely on the anaerobic system to help fuel your body. This is because a higher effort run requires more muscle recruitment, strength, and power. This requires more energy and quick production of it—both of which can only happen through the anaerobic pathway. Unfortunately, the anaerobic system can only supply energy for a finite period of time; the harder you work, the shorter the duration in which this system can provide energy.
Download RPE scale here.
What is Rate of Perceived exertion (RPE)?
The rate of perceived exertion is a grading system to gauge your effort level during cardiovascular exercise. The RPE scale has been backed by research to be a reliable estimate of how hard you are working and to which degree you are using a particular energy system to create the ATP that is fueling your activity.
Knowing which energy system you are primarily operating within is important because it guides two key things:
the intensity at which you should be training
the duration that you are able to perform your activity
As you can see in the RPE Scale, different RPE grades (0-10) correlate to different efforts of running.
The higher the RPE number, the higher your heart and respiratory rate.
As your heart/respiratory rate increases to a “deep and somewhat rapid” state (RPE 6), you start to tap into your anaerobic energy system to help create ATP (energy).
Whenever you start using the anaerobic system, lactate is produced as a byproduct. When lactate is produced at a higher rate than what your body can effectively process, you get an accumulation of lactate which can interfere with your muscle function. This starts to happen at RPE 9.
Training at RPE 6-8 will help you become better at processing and using lactate as an energy source.
Training at RPE 9-10 will help you become better at tolerating lactate build-up.
Because of the lactate build-up and the limited ability for the anaerobic system to provide energy for extended periods of time, you will only be able to run at these efforts for shorter periods of time as compared to relying predominantly on the aerobic system.
How is effort influenced?
Your RPE is influenced by intrinsic and extrinsic factors
Intrinsic factors — fatigue, stress, dehydration, illness, nutrition, blood sugar level
Extrinsic factors — pace, weather (heat, cold, humidity, wind), terrain (uphill, downhill, flat), altitude (low, high), type of shoes (carbon vs non-carbon)
How to use the RPE scale
By programming your training around specific RPE ranges you can ensure that you are utilizing the appropriate energy system for the duration and distance that you are attempting to run.
Additionally, training within specific RPE parameters will ensure that you are training for intended cardiovascular adaptations that will allow you to maximize your training without over-training, and you will be better able to manage your pacing on race day.
The RPE chart allows you to subjectively grade the effort level in which you are exercising by correlating it with a couple of self-checks—breathing rate and ability to talk.
RPE 0-2: Correlate to everyday activities. These activities rely solely on the aerobic energy system to fuel the processes needed to function.
RPE 3-5: Correlate to higher effort activities that rely on your aerobic energy system to fuel your body. This effort allows you to operate at higher heart rates for LONG periods of time.
RPE 6-10: Correlates to activation and progressive reliance on the anaerobic energy system to fuel your body, and less reliance on the aerobic energy system. This effort level allows you to operate at higher heart rates but for SHORTER periods of time. The higher the heart rate gets, the shorter the period of time you are able to operate in that pace.
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 (cardiovascular 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 someone who is experienced using the full range of RPE from 3 to 10 is appropriate as long as the higher level efforts are prescribed responsibly for the type of race for which you are training.
HOW DOES RPE RELATE TO training objectives?
If your workout objective is to actively recover, you should run at a RPE of 3.
If your workout objective is to improve the efficiency of your aerobic energy system, you should run at an RPE between 3-5.
If your workout objective is to improve your ability to run faster with less effort as well as become better at operating at your lactate threshold, your workout effort should be at a RPE range of 6 - 8. Over time, these workouts will allow you to improve from a 9:00/mile pace at RPE 4 to a 8:00/mile pace at the same RPE 4.
If your workout objective is to improve your ability to tolerate the build-up of lactate in your blood, increase your ability to perform intense workouts for long periods, or perform intense efforts repeatedly, then your workout should be at a RPE of 9-10.
Using the RPE grades also provides you a strategy that allows you to adjust your pace (faster or slower) depending on extrinsic and intrinsic factors. For example, on a very hot day you will need to adjust your running pace to be SLOWER than usual in order to maintain an RPE of 3-5 if your objective is to work on aerobic efficiency. On the flip side, if you are aiming to train in the RPE zone of 6-7 on a very hot day, you will not need to run as hard to achieve those ranges because your heart rate will elevate more readily in the hotter temperatures. In fact, if you try to run your “normal RPE 6-7 pace” on a very hot day, you will likely drive your effort level into the RPE 8-9 range, inhibiting you from attaining the benefits of a lactate threshold training session.
What if you don’t train energy systems appropriately?
If you aren’t holding yourself accountable to specific training paces you run the risk of:
over or under training
hitting the wall during your race or long runs
plateauing of your performance from season-to-season
injuring your tissue by working too hard and too much
FINAL THOUGHTS for distance running
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. 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). In short, your desired race pace is done. Your body will be forced to slow down considerably or even stop.
In 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 energy systems 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 if you don’t have enough fuel to power it. Just as drivers plan out their fuel usage when racing in order to optimize their performance, you too must do the same. Minding your RPE is an effective strategy to accomplishing this.