RPE or Rated Perceived Exertion is a metric used by many to self-measure exertion during physical exercise. While subjective in concept, the RPE scale, depending on which one you subscribe to can be a useful objective tool in measuring just how hard you are working.

Not that humankind didn't have effective ways of measuring the difficulty of workouts before with metrics such as sweating, vomiting or passing out, the RPE scale offers a numeric value based on physical sensations. The basis of RPE is perception, hence "perceived" exertion. This tenet means that there is a level of self-awareness that is required for the scale to be useful. The concept of a training age is a critical component of the effectiveness of RPE. Training age has several different variants that make it a valuable tool for managing athletes and their perceived rate of exertion. General training age refers to the number of years the person has spent in training and participating in various sports coupled with lifestyle habits that support the development of the athlete in that sport. Sport-specific training age refers to the number of years that an athlete has specialized in one particular sport. Developmental age refers to the degree of physical, mental, cognitive, and emotional maturity. Skeletal maturity or bone age can determine physical developmental age whereas mental, cognitive, and emotional maturity are then considered to determine developmental age (2).

The RPE Scale (or a variation thereof):
10: Maximal, no reps left in the tank
9: Last rep is tough but still one rep left in the tank
8: Weight is too heavy to maintain fast bar speed but isn't a struggle; 2–4 reps left
7: Weight moves quickly when is applied to the weight; "speed weight."
6: Light speed work; moves quickly with moderate force
5: Most warm-up weights
4: Recovery; usually 20 plus rep sets; not hard but intended to flush the muscle
An RPE below four isn't important.(1)

RPE vs. Percentages

Many traditional weightlifting and other strength and conditioning programs use percentages to calculate the prescribed difficulty of the lift. However even though percentage programs are easy to use, they're limited in how accurate they can be. Many things throw off your percentages. The longer you go in a training cycle, the less precise they become due to your strength adaptation. Each athlete is different because of differences in training history, fast to slow twitch ratios, illnesses, good and bad days, and general sleep patterns. Life happens, and you won't always be 100 percent when you come in to train (1).

Depending on your training age (the total amount of time you have followed a periodized strength and training program coupled with a proper lifestyle to support training) your percentages as a beginner lifter will be inaccurate. This reason, in particular, is why the BASIC program utilizes "heavy singles or heavy doubles." Most people don't know, or cant remember 1RMs. As a CrossFit coach, it's a popular response when a member looks at the workout that called for 8-10 Reps of a Back Squat at 65-70% and asks, "Well what if I don't know my 1RM"? This situation is where a coach can use RPE effectively. And let us be honest, most of us are neophytes when it comes to weightlifting.

RPE in Team Sports

There is a growing trend within the team sports community as well that uses RPE to manage players during matches effectively. For example, players either were training too little or too much depending on their role on the team. Starters who played every minute of every game were asked to perform the same training intensity as players who missed games and were fresh for every training session. Coaches in a variety of professional and semi-professional sports use RPE to manage their athlete's, and more importantly, the RPE scale teaches the value and importance of rest and recovery (3).

RPE is a useful metric to be used in your training as both a beginner or an advanced weightlifter. RPE forces self-reflection and honesty when it comes to measuring your training and accounts for this thing called life that often gets in the way of that training.

Sources:
(1) Tuchscherer, Michael "The Reactive Training Manual: Developing Your Own Custom Training Program for Powerlifting." c. 2009
(2) Istvan Balyi, Richard Way" Long-Term Athlete Development" c. 2015
(3) Cole, Troy: "The use of RPE in Team Sports": URL: https://simplifaster.com/articles/use-rpe-team-sports/ c.

Other Works Referenced:
1. Borg, G.A. (1982). “Psychophysical Bases of Perceived Exertion.” Medicine and Science in Sports and Exercise, 14(5), 377-381. URL: https://www.cdc.gov/physicalactivity/basics/measuring/exertion.htm
2. Impellizzeri, F.M., E. Rampinini, A.J. Coutts, A. Sassi, and S.M. Marcora (2004). “Use of RPE-Based Training Load in Soccer.” Medicine and Science in Sports and Exercise, 36(6), 1042-1047.