The Lengthened Partial ROM Myth: What Wolf et al. 2025 Actually Says (And Why Your Ego Hates It)

TL;DR on the data: The latest Bayesian analysis from Wolf et al. (2025) in PeerJ shows that lengthened partial repetitions (LPs) and full range of motion (fROM) produce identical hypertrophy when both emphasize the stretched position. Your ego wants you to believe one is superior. The physics says they're equivalent. The implication? You can stop ego-lifting through a half-rep range and actually train with precision.

The Setup: Why This Matters

For the past five years, the "lengthened partial ROM" (LP) literature has been building a compelling case: train at longer muscle lengths, and you'll get more hypertrophy. Kassiano et al., Pedrosa et al., and a meta-analysis by Wolf et al. (2023) all suggested LPs had a small edge over full ROM work.

So naturally, the internet did what it always does: it oversimplified the data into "half reps are better than full reps," and now your local gym is full of people doing quarter-depth squats and calling it "science."

Enter Wolf et al. 2025. This study is the corrective.

The Mechanistic Underpinnings

Here's the critical detail that changes everything:

The previous LP vs. fROM comparisons were comparing short-muscle-length training to long-muscle-length training.

In Pedrosa et al. (2022), for example, the LP group trained through roughly 100–65 degrees of knee flexion, while the fROM group trained through a more limited range. That's not a fair fight—of course the longer-length stimulus won.

But Wolf et al. 2025 did something different. They designed a study where both conditions emphasized the lengthened position. In the fROM condition, participants trained through full ROM with a 1-second pause in the stretched position. In the pROM condition, they trained through approximately 50% of their full ROM, but from the stretched position.

The result: Bayes factors of 0.16 to 0.39 across all outcomes, providing "moderate to anecdotal" support for the null hypothesis—i.e., no meaningful difference.

Both groups improved muscle thickness similarly. Both improved strength-endurance identically. The central estimates of group differences were essentially zero.

Why This Demolishes the LP Hype

Let's be direct: the previous studies weren't wrong. They were just incomplete. They showed that longer-muscle-length training is superior to shorter-muscle-length training—a finding that's mechanistically sound and has nothing to do with ROM per se.

What Wolf et al. 2025 reveals is that the stimulus-to-fatigue ratio is what matters, not the ROM label.

Here's the physics: Muscle tension is highest at longer lengths (where the sarcomere is operating at a suboptimal angle). If you're training at longer muscle lengths—whether through full ROM with a pause or through a partial ROM from the stretched position—you're getting the same mechanical tension stimulus. The hypertrophic response follows.

The problem with the "lengthened partial" trend is that it became an excuse for ego-lifting. People started doing half-squats from the top, half-deadlifts from the hip, and calling it "science." But that's not training at longer muscle lengths; that's just moving less weight through a smaller range.

The Practical Implications

For the 1% trainee, this is liberating:

Full ROM is still optimal. If you can move through a full range of motion with control and end-range tension, do it. The data supports it.
Lengthened partials are a tool, not a hack. If you have mobility restrictions, joint issues, or you're using LPs as a finisher after full ROM work, they're effective. But they're not "better."
The emphasis must be on the lengthened position. Whether you're using full ROM or partials, you need to spend time under tension at longer muscle lengths. A 1-second pause in the stretched position matters more than the ROM label.
Stop chasing ROM percentages. RPE-based training is superior to "half-rep" prescriptions. If you're stopping short of full ROM to move more weight on the bar, you're optimizing for ego, not hypertrophy.

The Study Design (Why It's Credible)

Wolf et al. 2025 is a within-participant study with 25 trained individuals (final sample; started with 30). Key design strengths:

Bayesian framework: Instead of the binary "p < 0.05" nonsense, the researchers used informative priors from previous meta-analyses and reported credible intervals. This is statistically honest.
Blinded assessments: The ultrasound technician measuring muscle thickness was blinded to condition allocation. The statistician was blinded to condition.
Ecological validity: This was a multi-exercise routine (chest press, rows, triceps, curls) over 8 weeks, not a single-exercise lab protocol. It actually resembles real training.
Trained population: All participants had at least 6 months of consistent upper-body training experience. This generalizes to actual lifters, not untrained college students.
Rigorous ROM control: Research assistants ensured both conditions reached the longest achievable muscle lengths for each exercise. This wasn't sloppy.

The preregistration: Methods were preregistered on the Open Science Framework before data collection. That means the researchers couldn't p-hack or move the goalposts. (This is how science should work.)

The Nuance (Because It Matters)

Wolf et al. 2025 doesn't say "lengthened partials are useless." It says:

"For muscle hypertrophy, analyses showed moderate evidence in support of the null hypothesis across sites... These novel findings allow for considerable flexibility in exercise technique prescriptions. For example, if an experienced trainee is unable to perform a full ROM, or prefers to use pROM, the present evidence suggests the effectiveness of LP ROM RT is similar."

Translation: Both work. Full ROM is still the default. Use LPs if you have a legitimate reason (mobility, joint pain, etc.), not because they're "superior."

There's also an important caveat: This study looked at upper-body movements (chest press, rows, curls, triceps work). Lower-body data is less clear. The stimulus-to-fatigue ratio on a hack squat might differ from a dumbbell curl. But the mechanistic principle holds.

The Meta-Level Audit

Here's what bothers me about the fitness industry's response to the previous LP literature:

A small research finding gets amplified into a "hack." Researchers publish a legitimate study showing that longer-muscle-length training produces slightly more hypertrophy. The internet reads the headline, ignores the nuance, and suddenly everyone's doing half-squats and claiming it's "peak science."

This is the same mechanism that sells proprietary blends and "anabolic window" supplements. It's the same reason people think "toning" is a real adaptation.

The antidote is radical honesty: The data supports full ROM training with an emphasis on the lengthened position. If you want to use lengthened partials, use them intentionally—as a tool for addressing mobility limitations or as a finisher. Don't use them as an excuse to move more weight through a smaller range and call it "science."

The Stimulus-to-Fatigue Ratio (The Real Takeaway)

Wolf et al. 2025 is ultimately a study about stimulus-to-fatigue ratio—a concept I've hammered on repeatedly because it's the actual lever of hypertrophy.

Stimulus: Mechanical tension at longer muscle lengths. This is highest when you're training at the end-range of motion.

Fatigue: The accumulated metabolic and neural cost of the set. More ROM = more fatigue (assuming similar loading and RPE).

If you can get the same stimulus with less fatigue, you win. That's the case for lengthened partials in specific contexts (mobility-limited athletes, advanced trainees using them as finishers). But if you can tolerate full ROM, the stimulus is identical, and you're not sacrificing anything.

The key is intentionality. Are you using LPs because you've done the analysis and determined it's optimal for your context? Or are you using them because the internet told you they're "better"?

Now, Go Apply It

Here's the protocol:

Default to full ROM. If you can move through a complete range of motion with control, do it. Spend at least 1 second in the stretched position on every set.
Use RPE, not ROM percentages. Stop thinking "I'm doing 50% ROM lengthened partials." Start thinking "I'm training to RPE 8-9 at the longest muscle length I can safely achieve."
Assess your mobility. If you have genuine restrictions (ankle dorsiflexion limits on squats, shoulder mobility limits on bench), address them or adjust your ROM accordingly. But don't use "mobility" as an excuse to ego-lift.
Track stimulus, not volume. Volume is reps × sets × load. Stimulus is reps × sets × load × time-under-tension × mechanical-tension-at-length. The latter is what drives hypertrophy. LPs can increase stimulus-per-rep if they allow you to spend more time at longer lengths. But full ROM does the same thing if you pause at the bottom.
Own your choices. If you use lengthened partials, know why. If you use full ROM, know why. Don't hide behind "the science says" when the science actually says "both work if you emphasize the lengthened position."

The bottom line: Wolf et al. 2025 is a corrective to hype. It doesn't invalidate lengthened partial training. It invalidates the claim that lengthened partials are superior to full ROM when both emphasize the stretched position.

Your ego will resist this. It's easier to believe there's a "hack" than to accept that the fundamentals (full ROM, mechanical tension, progressive overload) are still the move.

But the data is clear. Now, go apply it.

Citation: Wolf, M., et al. (2025). Lengthened partial repetitions elicit similar muscular adaptations as full range of motion repetitions during resistance training in trained individuals. PeerJ, 13, e18904. https://doi.org/10.7717/peerj.18904

Previous meta-analysis: Wolf, M., et al. (2023). Does longer-muscle length resistance training cause greater longitudinal growth in humans? A systematic review. Sports Medicine - Open.