The most repeated hypertrophy finding of the decade, and the population everybody drops when they repeat it.
A lengthened partial is the bottom portion of a rep performed on its own, after the full-range set has already ended. The bottom half of an incline curl with the elbow still open. The bottom half of a leg curl. You reach failure, then keep going in the stretched range only, until the position itself collapses.
The claim underneath it is stranger than the technique. Where in the range you load a muscle appears to change how much it grows, independently of how heavy the load was and how many sets you did. Two lifters can match weight, reps, sets and effort exactly, load different portions of the range, and not get the same result. If that is true, then "how much did you do" was never the whole question.
The study everyone cites is a 2022 knee-extension trial from Pedrosa and colleagues, with Brad Schoenfeld among the authors. Forty-five untrained women, randomised across a control group and four different range-of-motion conditions, one exercise. Partial reps performed at long muscle lengths came out favourably against the alternatives.
Now read the population again, because it is the part that never survives a repost. Forty-five untrained women, on a leg extension machine, doing one movement. That is a real randomised controlled result and it is a narrow base for a philosophy about how you should finish every set of every lift. Both halves of that sentence are true at once, which is an uncomfortable place to write from and the honest one.
The idea is older than the current wave, which is the better reason to take it seriously. McMahon and colleagues ran an eight-week trial published in 2014, loading the quadriceps either shortened, through zero to fifty degrees of knee flexion, or lengthened, through forty to ninety. Eleven participants in one group, ten in the other, indexed as a pilot. Small, but pointing the same direction a decade earlier.
In practice the method changes exactly one moment: what happens when a set ends. Instead of racking the weight at failure, you continue in the bottom third until the stretched position breaks down. The set gets longer without getting heavier, and that is the entire appeal. The cost lands on the muscle rather than on your joints, your central nervous system, or the four days afterwards.
It also only works where a loaded stretch exists. Incline curls, deep dumbbell presses, seated leg curls, Romanian deadlifts, pec deck. A lateral raise has almost no resistance at the bottom, so partials there buy you a burning sensation and very little else. Picking the wrong exercise is the most common way to run this method and get nothing.
You are on the last set of incline dumbbell curls, 14 kg, aiming for 10. You get 9 and the tenth stalls halfway. That is the end of the set as most people run it: rack them, note 9, move on.
Run it as a lengthened partial instead and the set is not over. You keep the dumbbells moving through the bottom third of the range, arm nearly straight, elbow behind the torso where the biceps is longest, until you cannot control the bottom position any more. Maybe six of those. Maybe four.
The log line reads 14 kg x 9, same as before. The set was meaningfully harder and you added no weight, no extra set, and about twenty seconds.
Prescribed as: 3 x 8-10 @ RIR 1, lengthened partials on the final set.
Lengthened partials exist in the app as an intensifier attached to the exercise, not as a note in a description field. That matters because an intensifier is a thing the readiness engine can reason about, and a note is not.
When you report high soreness or poor readiness, the adjustment ladder eases intensifiers before it touches your working weight. Lengthened partials come off before the load does, because losing the intensifier costs you a little stimulus and losing the load costs you the session's purpose.
The prescription travels with the set, so "partials on the last set" appears on the set you are about to do rather than in a plan document you read three weeks ago and half remember. That is the whole reason the intensifier is structured data.
The papers behind the empirical claims on this page, with the population each one studied. Where we could confirm only what a study set out to measure and not the size of what it found, the note says so rather than borrowing the paper's authority for a number nobody read.
Gustavo F Pedrosa et al. (2022). Partial range of motion training elicits favorable improvements in muscular adaptations when carried out at long muscle lengths. European Journal of Sport Science.
Compared strength and regional hypertrophy across different ranges of motion in the knee extension. Partial reps performed at long muscle lengths came out favourably against the other conditions.
45 untrained women, knee extension only, randomised across a control group and four range-of-motion conditions.Gerard McMahon et al. (2014). Muscular adaptations and insulin-like growth factor-1 responses to resistance training are stretch-mediated. Muscle & Nerve.
Tested whether altering muscle stretch during resistance training changes the adaptation, by loading the same muscle in a shortened versus a lengthened position for 8 weeks.
21 participants over 8 weeks, quadriceps loaded shortened (0-50 degrees knee flexion, n=10) or lengthened (40-90 degrees, n=11), then 4 weeks detraining. Indexed as a pilot project.Partial reps performed only in the stretched portion of a movement, usually immediately after a full-range set has reached failure. On an incline curl that means the bottom third with the arm nearly straight. The set continues in the range where the muscle is longest, until you can no longer control that position.
The research is genuinely promising and genuinely narrow. Pedrosa and colleagues found partials at long muscle lengths came out favourably in a randomised knee extension trial, but that trial used 45 untrained women on one machine. An earlier eight-week pilot by McMahon and colleagues pointed the same way with 21 participants. Treat it as a well-supported reason to end accessory sets this way, not as proof that full reps are obsolete.
Only ones where the stretched position is actually loaded and the movement is stable. Incline curls, deep dumbbell presses, seated leg curls, Romanian deadlifts and pec deck all qualify. Lateral raises and most bottom-range cable work do not, because tension disappears exactly where you would be doing the partials. Heavy barbell compounds are a bad idea for a different reason: failing a partial squat is dangerous.
No. It is an intensifier, and applying an intensifier everywhere just raises your training load while making it harder to tell what caused what. The usual application is the last set of an accessory movement, in the back half of a block, once adding weight has stopped being easy. If you are still progressing by putting more on the bar, do that instead.
Describe what you are training for and Fire Your Coach builds the block, carries the prescription onto the set, and remembers what the method actually produced.