Lab Notes · 5 min read
Every gym you have ever trained in decided your weight, your sets and when to stop with one instrument. That instrument is how the set felt to you. This Lab Note is about how well that instrument works, because researchers have been testing it for thirty years.
In one study, researchers secretly watched 44 adults through an hour of activity they chose themselves. Afterwards they asked each person to recall what they had done. The time spent sitting was underestimated. The aerobic work was overestimated by more than 300%, and men overestimated more than women.
Klesges et al., Medicine & Science in Sports & Exercise 1990;22(5):690–697
The same thing shows up in exercise logs. Adults over 45 kept a diary of a twelve-week home strengthening program while a hidden accelerometer counted the same exercises. Over the twelve weeks, the diaries recorded more work than the accelerometers counted.
Nicolson et al., Journal of Orthopaedic & Sports Physical Therapy 2018;48(12):943–950
Rating how hard you are working has a name. It is called the rating of perceived exertion, or RPE. In the Look AHEAD trial, 3,582 adults rated their effort at the level that is supposed to mean moderate, and their heart rates were checked at the same moment. Close to half of them were outside the moderate range.
Unick et al. (Look AHEAD), Journal of Novel Physiotherapy and Physical Rehabilitation 2014
Lifting has its own version. The number of repetitions you could still do before failure is called reps in reserve. It is how most coaches decide whether a set was hard enough. A review that pooled every study testing it found people guessed wrong, and their guesses only improved once the set was already close to failure. Years of training did not make anyone better at it.
Halperin et al., Sports Medicine 2022;52(2):377–390
Even well-trained men squatting to failure misjudged how many reps they had left, and they were furthest off early in the set. The longer the set, the worse the guesses got.
Zourdos et al., Journal of Strength and Conditioning Research 2021;35(2S):S158–S165
This is the one that costs people the most. Trained men were asked to choose the weight they would use for a set of ten. Then they did as many reps as they could with it. Most of them got far more than ten, because the weight they chose was too light for the job they chose it for.
Barbosa-Netto et al., Journal of Strength and Conditioning Research 2021;35(2S):S166–S172
A review of eighteen studies found the same thing. When people choose their own weights, they choose about half of what they can lift. That is below the range that builds strength.
Steele et al., Sports Medicine 2022;52(12):2909–2923
That is not a judgment on anyone. Effort is hard to read from the inside because fatigue, mood, sleep and the room all change how a set feels. The feeling is real. It just does not measure the thing it is being used to measure.
The whole gym runs on an AI-based strength measurement system. Artificial intelligence reads exactly what level of effort you are putting in on every repetition, and it makes sure you are in the right strength-building and muscle-building zone at all times. No junk reps.
So the weight in your hands is set by what you are actually producing on the day, and the set ends when the work is done. You still feel every set. The difference is that the feeling no longer has to make the decision.
Every study in this Lab Note, and the rest of the research we build on, is on The Research page with a link to the paper.
Twenty-five minutes. No charge. You walk out with your numbers.
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