When people lift weights through a full motion vs. just part of the motion, the muscles might look like they grow more in one case—but that could just be because the weight feels heavier at different points, not because the muscle is stretched more. So we can’t be sure if stretching the muscle is what’s causing the growth.
From We Need to Talk About Jeremy Ethier’s New Study · videoSee the scientific wording
When comparing full range of motion resistance training to lengthened partial range of motion resistance training, observed differences in muscle hypertrophy may be confounded by variations in the location of peak resistance along the joint angle spectrum, thereby complicating the ability to isolate the independent effect of muscle length on hypertrophy.
Very strong evidence
Randomized trials4 good-quality studies support this claim.
What the research says
4 studies reviewedSupporting (4)
Randomized Controlled TrialHuman2025
The study found that lifting weights through a partial range (stretched position) and full range gave the same muscle growth, even though the resistance felt different at the top or bottom. This supports the idea that it’s hard to tell if muscle length alone causes differences — because other factors like where the weight feels heaviest might be messing with the results.
Systematic Review With Meta-AnalysisMeta-analysis
This study looked at whether doing partial lifts with muscles stretched (long length) vs. shortened (short length) makes muscles grow differently — and it found that muscle length itself matters, not just where the weight feels heaviest. So yes, it supports the idea that peak resistance isn't the only thing causing growth differences.
Which ROMs Lead to Rome? A Systematic Review of the Effects of Range of Motion on Muscle Hypertrophy
Systematic Review With Meta-AnalysisMeta-analysis2023
The study found that where you stop or start your exercise matters more than just how far you stretch the muscle — meaning it’s not just muscle length causing growth, but where the hardest part of the lift happens.
Contradicting (0)
No contradicting studies found yet
That doesn't mean it's settled — it just means no study has tested the opposite.
Quality-weighted scoring: we follow the GRADE framework — each study is rated High, Moderate, Low, or Very Low based on study design, methodology rigor, and risk of bias. A single high-quality RCT can outweigh several weaker observational studies.
Scores reflect study quality, not just count.
When you lift weights with your muscles stretched long, your muscle fibers get pulled and feel tension. This tension sends a signal inside the muscle cells that tells them to grow bigger. Even if the weight feels heaviest at a different point, as long as the muscle gets stretched enough, it grows. So both stretching and where the weight is heavy matter, but stretching seems to be the main trigger for growth.
Score breakdown, mechanism chain, raw evidence, ideal studies needed & 4 supporting studies
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When people lift weights through a full motion vs. just part of the motion, the muscles might look like they grow more in one case—but that could just be because the weight feels heavier at different points, not because the muscle is stretched more. So we can’t be sure if stretching the muscle is what’s causing the growth.
Mechanism
4 studiesWhen you train with muscles stretched long, the pulling signal makes them grow. The weight being heavy at a different spot doesn't stop the growth as long as the stretch is there. So the main thing for muscle growth is how stretched the muscle gets, not just where the weight is hardest.
When you lift weights with your muscles stretched long, your muscle fibers get pulled and feel tension. This tension sends a signal inside the muscle cells that tells them to grow bigger. Even if the weight feels heaviest at a different point, as long as the muscle gets stretched enough, it grows. So both stretching and where the weight is heavy matter, but stretching seems to be the main trigger for growth.
Resistance training at long muscle lengths creates mechanical tension and passive stretch on muscle fibers.
The mechanical stretch is detected by mechanosensors (integrins, stretch-activated channels) on the muscle cell membrane, activating intracellular signaling pathways such as focal adhesion kinase and the PI3K/Akt/mTOR cascade.
Activation of these signaling cascades promotes muscle protein synthesis, leading to increased muscle fiber size (hypertrophy).
The location of peak resistance modifies the distribution of mechanical tension along the muscle but does not override the influence of muscle length on the stretch stimulus; when training includes adequate stretch, hypertrophy is similar regardless of peak resistance location.
Evidence from Studies
Supporting (4)
Community contributions welcome
The study found that lifting weights through a partial range (stretched position) and full range gave the same muscle growth, even though the resistance felt different at the top or bottom. This supports the idea that it’s hard to tell if muscle length alone causes differences — because other factors like where the weight feels heaviest might be messing with the results.
Muscle hypertrophy from partial repetition at long vs. short muscle length: A systematic review and meta-analysis
This study looked at whether doing partial lifts with muscles stretched (long length) vs. shortened (short length) makes muscles grow differently — and it found that muscle length itself matters, not just where the weight feels heaviest. So yes, it supports the idea that peak resistance isn't the only thing causing growth differences.
Which ROMs Lead to Rome? A Systematic Review of the Effects of Range of Motion on Muscle Hypertrophy
The study found that where you stop or start your exercise matters more than just how far you stretch the muscle — meaning it’s not just muscle length causing growth, but where the hardest part of the lift happens.
The study says that when you train with a full range of motion, you might see more muscle growth—but that’s probably because the weights feel heavier at the stretched position, not just because the muscle is longer. So it’s hard to tell if length or resistance is the real reason.
1 study stuck in processing — a maintainer can requeue it.
Contradicting (0)
Community contributions welcome
1 study has been processing far longer than a normal run. The pipeline may be stuck — a maintainer can requeue it, and the results will appear here once it finishes.
Score Breakdown
No multi-axis breakdown available yet. The overall Pro / Against score above is the best signal.
- No clinical evidence is available; the score reflects mechanistic plausibility only.
What Would Prove This
Per GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this claim, ordered from strongest to weakest.
Whether muscle length alone drives hypertrophy when peak resistance is held constant across ROM conditions
Healthy resistance-trained adults (n=20) perform two 8-week training interventions in random order: (1) full ROM squats with added external resistance at the bottom to match peak torque of partial ROM, and (2) partial ROM squats (0–60° knee flexion) with resistance adjusted to match the torque profile of full ROM at all joint angles. Muscle thickness (ultrasound) and cross-sectional area (MRI) measured pre/post. All other variables (volume, intensity, rest) controlled. Primary outcome: hypertrophy difference between conditions when peak resistance is equated.
Whether muscle length at end-range correlates with hypertrophy when EMG activity and total tension-time are matched
15 participants perform two 6-week training protocols: (1) full ROM leg extensions with load adjusted so EMG activity and time-under-tension match those of (2) partial ROM leg extensions (45–90°) with added resistance at the lengthened position. Muscle fascicle length (ultrasound) and hypertrophy (MRI) tracked weekly. Peak torque is recorded at every 5° interval to confirm resistance profiles are matched. Primary outcome: correlation between end-range muscle length and hypertrophy after controlling for EMG and tension-time.
Whether muscle length at a fixed joint angle drives hypertrophy independent of movement dynamics
Participants (n=30) train one leg with isometric contractions at 120° knee flexion (lengthened position) and the other leg at 60° (mid-range), matched for total force-time integral and frequency. Resistance is applied via dynamometer with real-time feedback to ensure identical tension profiles. Muscle thickness and fiber length measured via MRI and ultrasound after 8 weeks. Primary outcome: hypertrophy difference between lengthened vs. mid-range isometric training when movement and peak resistance are eliminated as variables.
Whether hypertrophy differs when mechanical work and torque-angle curves are identical but ROM differs
Two groups matched for baseline strength: Group A performs full ROM bench press with variable resistance (bands/chains) to match the torque-angle curve of Group B’s partial ROM bench press (mid-range only). Both groups perform identical total mechanical work per session over 10 weeks. Muscle thickness (ultrasound) and pennation angle (Doppler) measured at pectoralis major insertion. Primary outcome: hypertrophy difference after controlling for total work and torque profile.
Whether existing studies show consistent hypertrophy differences after adjusting for peak resistance location
Meta-analysis of all RCTs comparing full vs. partial ROM resistance training. Individual participant data extracted to calculate and adjust for peak torque location (via torque-angle profiles reported or estimated from joint kinematics). Primary outcome: standardized mean difference in hypertrophy after covariate adjustment for peak resistance location. Secondary: subgroup analysis by muscle group (e.g., quads vs. pecs).