Train Where the Muscle Stretches

The science of lengthened-position training for maximum lower-body growth and why it’s one of the most debated topics in coaching today.

ONE OF THE MOST DEBATED QUESTIONS IN MODERN TRAINING

Ask ten coaches whether you grow more muscle by training in the stretch or the squeeze, and you may get ten different answers. This is one of the most genuinely contested topics in the fitness field right now so let’s look at what the evidence actually shows.

For most of training history, the muscle-building conversation centered on three things: how heavy you lift, how much you do, and how often. Where in the movement you loaded a muscle was barely discussed. In the last few years that has flipped. A wave of careful human studies many using MRI scans rather than simple tape measures suggests that loading a muscle while it is stretched can grow it more than loading it while it is contracted.^1,2

This has become a real point of disagreement. Some coaches treat “train the stretch” as a near-law. Others argue the effect is overstated and inconsistent. Both camps have evidence. This review walks through that evidence in plain language, shows where it is strong and where it is shaky, and because we are a lower-body academy first pays special attention to the glutes, hamstrings, quads, and calves before covering the rest of the body.

Author’s note: This article was researched, gathered, and synthesized by Navid Moravej as a literature review. It brings together findings from peer-reviewed trials and meta-analyses so that coaches and lifters at any level can understand and apply them. Full numbered references appear at the end.

New to the terms? A muscle is “lengthened” (or stretched) when it is pulled long like your hamstrings at the bottom of bending to touch your toes. It is “shortened” (or contracted) when it is bunched up like your biceps at the top of a curl. Every exercise has a stretched end and a squeezed end.

THE SCIENCE IN PLAIN ENGLISH When a muscle is loaded while stretched, it produces tension two ways at once: the active pull of the working fibers, plus the passive tension of the stretched tissue itself (think of stretching a rubber band). More total tension is the main signal that tells a muscle to grow.3 That is the leading reason training in the stretched position appears so effective.

THE TWO APPROACHES, SIDE BY SIDE

The whole debate comes down to two ways of biasing where the hardest part of a rep happens. You don’t have to pick only one full range of motion includes both but understanding them is the foundation.

Figure 1. The same muscle, two ends of one movement. Does loading the stretch (left) beat loading the squeeze (right)?

Lengthened / long-muscle-length (the stretch)

Loads the muscle where it is pulled long the bottom of a Romanian deadlift, a deep squat, a seated leg curl. Also called stretch-mediated hypertrophy, lengthened partials, or lengthened-state training.

Shortened / peak-contraction (the squeeze)

Loads the muscle where it is bunched up the top of a hip thrust, the lockout of a leg extension, the peak squeeze. Also called shortened partials or peak-contraction training.

When studies force a head-to-head choice, the stretched end usually wins or ties and rarely loses outright.^1,2 But “usually” is doing real work in that sentence, which is the heart of the controversy.

THE ONE IDEA THAT MAKES SENSE OF EVERYTHING: TWO-JOINT MUSCLES

Here is the concept that resolves most of the confusion. Some muscles cross only one joint; others cross two. The two-joint muscles (the technical word is biarticular) can be put into a deep stretch by moving the joint you’re not actively training and these are the muscles that benefit most from stretch-focused training.^4,5

Why this matters for the lower body: Your hamstrings and one of your calf muscles (the gastrocnemius) are two-joint muscles. That’s exactly why a seated leg curl (hip bent, hamstring stretched) and a standing calf raise (knee straight, calf stretched) grow those muscles more than their alternatives. The position of the “other” joint changes everything.

Figure 2. Same knee movement, different hip position. Bending the hip (seated curl) pre-stretches the hamstring — and grows it noticeably more than the lying version.

The flip side: muscles that cross only one joint (like the bulk of your quads, or the soleus deep in your calf) can’t be stretched much by repositioning, so for them the stretch-vs-squeeze debate barely matters — just train them through a full range and add weight over time.

LOWER BODY FIRST: WHAT THE EVIDENCE SAYS

Since this is where Booty Center lives, we’ll go muscle by muscle through the lower body before covering the rest.

Glutes — the most nuanced case (read carefully)

Here’s the honest truth that separates real coaching from slogans: the simple “always train the stretch” rule does not cleanly apply to your glutes. The gluteus maximus is mainly a one-joint hip extensor, and its leverage is strongest at full hip extension, the top of a hip thrust, not in a deep stretch.¹⁰

• A 2025 review of the research found glute growth is real and meaningful, and that exercises loading large hip extension, hip thrusts and deep squats, drive the strongest results.⁹
• A direct MRI study comparing the back squat and the hip thrust found similar glute growth from both, even though the squat loads the glute in a deeper stretch.¹⁰ That’s the key reason we don’t over-apply the stretch rule here.

WHERE COACHES DISAGREE: GLUTES One camp says deep, loaded stretch (deep squats, deficit work) is the key to glute growth. Another points to studies where hip thrusts, which load the squeeze, not the stretch, match or beat squats. The grounded takeaway: train glutes through a full range under load, keep both deep hip flexion and strong lockouts in your program, and don’t abandon the hip thrust just because it loads the short end.9,10

Hamstrings — the clearest stretch win in the lower body

This is where stretch-focused training shines brightest. Because the hamstrings cross two joints, bending the hip puts them in a deep stretch and training them there grows them substantially more.^5,6

COACH’S TIP HAMSTRINGS Favor the seated leg curl over the lying version, and include Romanian deadlifts and stiff-leg work for loaded deep stretch. For overall hamstring size, lengthened-state eccentric work beats Nordic curls.5,6

Quads it depends which part

The quad is four muscles. The rectus femoris (the one down the middle that also crosses the hip) responds to stretch positioning leg extensions with the torso more reclined load it longer.⁸ The other three (the vasti) cross only the knee, so for them a full-range squat or leg press is plenty and position barely matters.²

Your calf has two main muscles. The gastrocnemius (the visible diamond) crosses the knee, so a standing calf raise (knee straight) stretches and grows it far more than a seated one.⁷ The soleus underneath crosses only the ankle, so the seated raise is perfectly fine for it. Train standing for shape, seated for completeness.

COMPREHENSIVE COVERAGE: THE REST OF THE BODY

A complete physique needs more than lower body, so here’s how the same principle applies up top.

Triceps — the biggest stretch effect anywhere

The long head of the triceps crosses the shoulder, so doing extensions with the arm overhead puts it in a deep stretch and grows the triceps substantially more than pressdowns with the arm by your side.⁴ If you do one thing for bigger arms, add an overhead extension.

Biceps — genuinely unsettled

The biceps is the clearest example of the ongoing debate. One well-known study found the stretched position (incline curls, arm behind the body) grew them more.¹¹ Another, carefully matched study found no difference between stretched and shortened positions.¹² Honest verdict: incline curls are a reasonable bet, but don’t treat it as settled.

THE MUSCLE-BY-MUSCLE VERDICT

Lower-body muscles are shaded green. “Advantage” reflects how big the stretch-position benefit is in the best current studies.

MUSCLE	BEST POSITION	LENGTHENED PICK VS. SHORTENED	ADVANTAGE	KEY EVIDENCE
Glutes (gluteus max.)	Full hip extension*	Hip thrust / deep squat — load full range	Small / unsettled	Krause Neto 2025 [9]; Plotkin 2023 [10]
Hamstrings (BFlh, SM)	Lengthened	Seated leg curl (hip bent) > lying curl	Large	Maeo 2021 [5]
Hamstrings (overall)	Lengthened	Lengthened-state eccentric > Nordic curl	Moderate	Maeo 2024 [6]
Quads (rectus femoris)	Lengthened	Leg ext., torso reclined > upright	Moderate	Larsen 2025 [8]
Quads (vasti, 1-joint)	Position-neutral	Full-ROM squat / leg press — either works	Trivial	ROM meta [2]
Calves (gastrocnemius)	Lengthened	Standing (knee straight) > seated raise	Large	Kinoshita 2023 [7]
Calves (soleus)	Position-neutral	Seated raise is fine (1-joint muscle)	Trivial	Kinoshita 2023 [7]
Triceps (long head)	Lengthened	Overhead extension > neutral pressdown	Large	Maeo 2023 [4]
Biceps	Lengthened (contested)	Incline curl vs preacher — mixed results	Small / mixed	Sato 2021 [11]; Nunes 2024 [12]

*Glutes: the advantage is about loading through full hip extension, not simply “going deep,” and direct head-to-head trials are still limited – see the glute section above.

HOW BIG IS THE DIFFERENCE?

To make the numbers concrete: in a within-participant hamstring trial, the biceps femoris long head grew +14.4% from seated (stretched) curls vs. +6.5% from lying (shortened) curls, and the semimembranosus +8.2% vs. +3.6%.⁵ In the calf, the gastrocnemius grew about +12.4% standing vs. roughly +3.7% seated.⁷ Two of the three biggest position effects in the literature are lower-body muscles – which is good news for how we train at Booty Center.

Figure 3. Percent muscle growth by training position in controlled trials. Within-participant designs; values as reported by the original authors.

PUTTING IT TO WORK: SIMPLE RULES

1. For two-joint muscles, pick the exercise that stretches them

This is where the easy wins live same effort, more growth, just from smarter exercise choice. In the lower body that means seated leg curls and standing calf raises; up top, overhead triceps work.^4,5,7

2. Own the stretch don’t bounce out of the bottom

The benefit comes from staying loaded in the stretched position. Lower the weight under control, pause briefly at the deep point, and resist the urge to bounce or relax at the bottom.^1,3

3. Treat lengthened partials as a useful tool, not magic

Reps done only in the stretched range can match or modestly beat full-range work for some muscles and are a good way to add stretch-focused volume but they’re a variation, not a replacement for full-range strength.^1,13

4. For glutes and one-joint muscles, train the full range and add load

Glutes, vasti, and soleus don’t follow the simple stretch rule. Train them through a complete range, keep your hip thrust lockouts strong, and focus on progressively adding weight.^2,9,10

KEY TAKEAWAY “Stretch-mediated hypertrophy” is really just load-the-muscle-while-it’s-long training. The stretch itself isn’t magic the tension it creates is. Biggest, clearest wins: hamstrings and gastrocnemius (lower body) and the triceps long head (upper). Most nuanced: glutes and single-joint muscles.

WHY THIS TOPIC STAYS CONTROVERSIAL

It’s worth being clear about why smart coaches still disagree. Several respected analysts argue the phrase “stretch-mediated hypertrophy” is overhyped, since in a working muscle the growth isn’t caused by stretch alone.¹⁴ When researchers combine all the range-of-motion studies, the average difference between full and partial range is often small, and a full or long range works well for most goals.² The dramatic effects show up mainly in specific isolated two-joint muscles which is exactly why this article points you to those cases (hamstrings, gastrocnemius, triceps) rather than claiming the stretch always wins. Use it as a guide for choosing exercises, not as an unbreakable law.

TRAIN GLUTES & LOWER BODY THE EVIDENCE-BASED WAYThis is exactly how we build programs at Booty Center — every exercise chosen for a reason, every rep loaded where it counts, and every claim backed by research instead of hype. Ready for a lower-body plan built on this science?→  Get coached at bootycenter.com

This article is educational and not a substitute for individualized medical or coaching advice. Train within your ability, progress gradually, and consult a qualified professional for any injury concerns.

REFERENCES

1. Nuckols G. Why stretch-mediated hypertrophy is overhyped. Stronger by Science. 2024.
2. Wolf M, Androulakis-Korakakis P, Piñero A, et al. Lengthened partial repetitions elicit similar muscular adaptations as full range of motion repetitions during resistance training in trained individuals. PeerJ. 2025;13:e18904.
3. Wolf M, Androulakis-Korakakis P, Fisher J, Schoenfeld B, Steele J. Partial vs full range of motion resistance training: a systematic review and meta-analysis. Int J Strength Cond. 2023;3(1).
4. Warneke K, Lohmann LH, Lima CD, et al. Physiology of stretch-mediated hypertrophy and strength increases: a narrative review. Sports Med. 2023;53(11):2055–2075.
5. Maeo S, Wu Y, Huang M, et al. Triceps brachii hypertrophy is substantially greater after elbow extension training performed in the overhead versus neutral arm position. Eur J Sport Sci. 2023;23(7):1240–1250.
6. Maeo S, Meng H, Yuan X, et al. Greater hamstrings muscle hypertrophy after training at long versus short muscle length (seated vs. lying leg-curl trial). 2021.
7. Maeo S, Balshaw TG, Nin DZ, et al. Hamstrings hypertrophy is specific to the training exercise: Nordic hamstring versus lengthened-state eccentric training. Med Sci Sports Exerc. 2024;56(10):1893–1905.
8. Kinoshita M, Maeo S, Kobayashi Y, et al. Triceps surae muscle hypertrophy is greater after standing versus seated calf-raise training. Front Physiol. 2023;14:1272106.
9. Larsen S, Kristiansen BS, Swinton PA, et al. The effects of hip-flexion angle on quadriceps femoris muscle hypertrophy in the leg-extension exercise. J Sports Sci. 2025;43:210–221.
10. Krause Neto W, et al. The impact of resistance training on gluteus maximus hypertrophy: a systematic review and meta-analysis. Front Physiol. 2025;16:1542334.
11. Plotkin DL, Rodas MA, Vigotsky AD, et al. Hip thrust and back squat training elicit similar gluteus maximus hypertrophy and transfer similarly to the deadlift. Front Physiol. 2023;14:1279170.
12. Sato S, Yoshida R, Kiyono R, et al. Elbow joint angles in elbow-flexor unilateral resistance exercise training determine its effects on muscle strength and thickness. Front Physiol. 2021;12:734509.
13. Nunes JP, et al. Comparison between shoulder-flexed and shoulder-extended positions in elbow-flexion resistance training on regional hypertrophy and maximum strength (preacher vs. Bayesian cable curls). 2024/2025.
14. Pedrosa GF, Simões MG, Figueiredo MOC, et al. Training in the initial range of motion promotes greater muscle adaptations than at the final range in the arm curl. Sports. 2023;11(2):39.