Train the stretch
Range of motion is the most underrated variable in the gym. Loading a muscle at long lengths builds more of it — and it changes which exercises are worth doing.
Founder of Vertex Strength LabPublished · Updated
Short answer
Train through a full range of motion and choose exercises that load the muscle hardest when it is stretched. In studies, training only the lengthened half of a movement matched or slightly beat full range for growth, while training only the shortened half was clearly worse. Lengthened partials work best added at the end of a set.
Most people treat range of motion as a technique detail — something to tidy up once the weight is where they want it. It is closer to a training variable in its own right, and one of the few where the evidence has moved decisively in the last five years.
The finding, put simply: muscle grows most where it is loaded while stretched.
Full ROM
Beats partial range in almost every comparison
Long lengths
Where the extra growth actually comes from
Full range beats partial range: does range of motion matter?
Start with the uncontroversial part. When studies compare a full range of motion against a shortened one at matched load and sets, full range wins for hypertrophy — usually comfortably, and often for strength across the whole range too.
That result is intuitive if you think about total work: a deeper squat moves the bar further, so the muscle does more mechanical work per rep. But there is a second mechanism that turns out to matter more.
The stretched half does the work.
Relative hypertrophy from training the same exercise through different portions of its range, indexed to full range.
Shortened half
top of the curl
Full range
the standard
Lengthened half
bottom of the curl
Training only the stretched portion of a movement matches or slightly beats training the full range (Pedrosa et al. 2022; Kassiano et al. 2023). Training only the shortened portion is clearly worse. That asymmetry is the whole story: it is not the distance travelled that matters most, it is where the tension is applied.
Stretch
A muscle under load at long length produces a disproportionate growth signal. This is why a deep stretch on a Romanian deadlift builds more hamstring than a heavier one done to the knees.
This changes exercise selection: which exercises train the stretch
If loading at long lengths is what pays, then exercises stop being interchangeable. The question for any movement becomes: is the muscle under meaningful tension when it is at its longest?
For a lot of gym staples, the answer is no. Cable and machine exercises in particular often peak in resistance exactly where the muscle is shortest, which is the least useful place to be hardest.
Which exercises actually train the stretch.
S
Heavy tension at full stretch
Romanian deadlift
Hamstrings
Deep squat
Quads · glutes
Incline dumbbell curl
Biceps
Overhead cable triceps extension
Triceps
Deficit calf raise
Calves
Dumbbell flye / deep press
Chest
A
Good range, moderate stretch load
Pull-up, full hang
Lats
Bulgarian split squat
Quads · glutes
Chest-supported row
Upper back
Leg curl, seated
Hamstrings
C
Hardest where the muscle is shortest
Standing cable curl
Biceps
Triceps pushdown
Triceps
Leg extension, upright
Quads
Standing calf raise, no deficit
Calves
Two notes on that C tier, because it always causes arguments. Those exercises still build muscle. They are simply the less efficient option when a stretch-loaded alternative for the same muscle exists and costs you nothing extra. A seated leg curl loads the hamstrings at longer lengths than a lying one, for exactly this reason, and grew them more in a head-to-head trial.
Lengthened partials, used properly: how to apply them
The natural next question is whether you should stop doing full reps and only do the bottom half. Mostly, no — but there is one place it is genuinely useful.
Four practical changes.
1
Use full range as the default
Full range gives you the stretch plus the strength across the whole movement. Partials are a supplement to it, not a replacement.
2
Add lengthened partials at the end of a set
When full reps fail, continue with partial reps in the bottom half. You extend the set in the most productive part of the range instead of stopping.
3
Pick the stretch-loaded variant
Incline curl over standing curl. Overhead extension over pushdown. Seated leg curl over lying. Same muscle, same effort, better position.
4
Control the eccentric into the stretch
Two seconds down, no bouncing out of the bottom. The stretched position is where the growth signal lives and also where the injury risk is — earn it slowly.
The one caution
Loading a muscle at its longest length is also the most mechanically demanding thing you can ask of it. That is why it works, and it is why it needs to be approached with a bit of respect.
Deep stretch under heavy load, performed suddenly, with a bounce, on a muscle that has never been there before, is how people strain hamstrings and pecs. Build into the range over weeks. Control the descent. Do not let a barbell drop into a position your tissue has not been trained to accept.
"Half reps let you use more weight, so you get more out of the set."
The wrong half
Key numbers
| Part of the range trained | Relative growth |
|---|---|
| Shortened half only | About 60 |
| Full range | 100 |
| Lengthened half only | About 105 |
Indexed to full range. Default to full range, and add lengthened partials when full reps fail.
The short version
Take every rep through its full range, and choose the version of each exercise that keeps tension on the muscle when it is longest. When a set ends, a few extra partial reps in the stretched position are worth more than a few in the top half.
Range of motion is free progressive overload. Most people are leaving it on the floor at the bottom of every rep.
Common questions
Are partial reps good for muscle growth?
Only the right half. Partial reps in the lengthened, stretched part of the range match or slightly beat full reps, while partials in the shortened top half build clearly less.
What are lengthened partials?
Partial reps done in the bottom, stretched portion of an exercise. They work best added at the end of a set, after full reps fail, to extend the set in the most productive part of the range.
Which exercises load the muscle at long lengths?
Romanian deadlifts, deep squats, incline dumbbell curls, overhead cable triceps extensions, deficit calf raises and dumbbell flyes or deep presses all keep heavy tension at full stretch.
Is a seated or lying leg curl better?
Seated. Hip flexion puts the hamstrings at a longer length throughout the movement, which is why the seated version is the better choice for growth.
Is training at long muscle lengths risky?
It is the most demanding position for a muscle, so build into it over weeks, control the lowering, and never bounce a heavy load into a stretch your tissue is not used to.
References
- Pedrosa GF, Lima FV, Schoenfeld BJ, Lacerda LT, Simões MG, Pereira MR, et al. Partial range of motion training elicits favorable improvements in muscular adaptations when carried out at long muscle lengths. European Journal of Sport Science. 2022;22(8):1250–1260. doi:10.1080/17461391.2021.1927199
- Kassiano W, Costa B, Kunevaliki G, Soares D, Zacarias G, Manske I, et al. Greater Gastrocnemius Muscle Hypertrophy After Partial Range of Motion Training Performed at Long Muscle Lengths. Journal of Strength & Conditioning Research. 2023;37(9):1746–1753. doi:10.1519/jsc.0000000000004460