Regional Hypertrophy: Can You Grow Proximal, Middle or Distal Muscle Regions?

Regional hypertrophy is real, in the sense that muscles do not grow evenly from end to end. Imaging studies keep finding that one site gains more than another. What the research has not shown is that you can switch one region on and leave the rest asleep.

This article sits inside our guide to muscle length, range of motion and stretch-mediated hypertrophy. Here we stay on one question: when you ask “can I grow my lower biceps, inner chest or the bit above my knee?”, what do MRI and ultrasound studies actually say?

What is regional hypertrophy?

Regional hypertrophy means different parts of one muscle grow by different amounts. “Regions” usually means proximal (closer to the trunk), middle, and distal (closer to the elbow or knee). It can also mean one head of a muscle versus another, like the rectus femoris versus the vastus lateralis in the quads.

Researchers can only detect this with direct measurements such as muscle thickness, cross-sectional area or volume taken at several sites. A single measurement misses it. A 2024 methods paper makes the point bluntly: muscle size changes vary across regions within and between muscles, and architecture changes such as fascicle length and pennation angle are also region-specific (Nunes et al., 2024).

So the idea itself is not broscience. The leap people make from it is where things get shaky.

What do MRI and ultrasound studies show?

Let’s start with the structural evidence, muscle by muscle.

Triceps: where the muscle works hardest is where it grows

Two MRI studies from the same Japanese group are the clearest pair. In the first, 12 young men trained the elbow extensors with a multijoint exercise for 12 weeks. The middle regions of the triceps brachii were more activated in the first session and also showed bigger relative growth than the most proximal region (Wakahara et al., 2013).

In the earlier study, activation after one session was lower in the distal region than the middle and proximal regions, and the 12-week gain in cross-sectional area was also smaller distally (Wakahara et al., 2012). Both papers conclude that the regional difference in growth tracks the regional difference in activation during training.

Notice that the two studies disagree slightly on the proximal region. That is normal. Different exercises, small samples (12 per group) and slightly different measurement sites will do that.

Quadriceps: exercise choice changed the pattern

The quads give us the cleanest “same volume, different exercise” test. In a randomized trial, two groups matched for training volume and intensity performed either Smith machine squats or leg extensions. All three regions of the rectus femoris (proximal, central, distal) grew significantly in the leg extension group, while in the squat group only the central region of the vastus lateralis grew significantly (Zabaleta-Korta et al., 2021).

The authors conclude that exercise selection plays a role in regional hypertrophy, with other factors possibly involved too.

A second study used ultrasound in 36 men who were not strength-trained, split into heavy squat, jump squat and control groups. After 8 weeks, heavy squats and jump squats grew the vastus lateralis and intermedius at mid-thigh, but they differed in where else the vasti grew (the abstract is not fully consistent about which grew proximally and which distally). No rectus femoris growth appeared at any site in either squat group (Earp et al., 2015).

Put the two together and you get a consistent message: squat-type training and leg extensions do not grow the quads in the same pattern, and the rectus femoris in particular seems to respond better to an exercise that works the knee extension without much hip involvement. That second part is my interpretation, not a finding either study tested directly.

Biceps: the “lower biceps” claim does not hold up well

Curl variations are where the internet gets most specific. A 2025 within-subject trial put 15 young men through 10 weeks of unilateral curls, one arm with the shoulder flexed (preacher curl), the other with the shoulder extended (Bayesian cable curl), with resistance profiles matched. Muscle thickness rose at the proximal, mid and distal biceps in both conditions, with no significant difference between them (Attarieh et al., 2025). Both conditions grew each region by roughly 6-9%.

So a different shoulder position did not obviously change the regional pattern here. If you want the full exercise comparison, see our breakdown of preacher curls versus Bayesian cable curls.

Why do muscles grow unevenly?

Nobody has a complete answer. The best-supported piece is activation: the triceps MRI work links where a muscle is recruited hardest in a session to where it grows afterwards. A muscle is not a single switch. Parts of it can be loaded harder depending on joint angle, the resistance profile of the exercise and where fatigue builds up.

Other factors are often suggested. These include how muscle fibres are arranged and angled, the fact that large muscles have distinct parts that the nervous system can recruit somewhat separately, and the length the muscle is trained at. These are reasonable hypotheses, but I would not state any of them as proven for a particular exercise.

Muscle length is the one with some systematic evidence. A review of 11 range-of-motion studies found that full range, or partials in the initial (stretched) part of the range, beat partials in the final (shortened) part for growth at distal sites of the rectus femoris, vastus lateralis, biceps brachii and brachialis. Interestingly, partials in the initial range produced more proximal rectus femoris growth than full range (Kassiano et al., 2023). Different regions, different best strategies.

What does the conflicting evidence say?

This is where honesty matters, because the regional story is not clean.

• Leg press range of motion. In 23 resistance-trained people doing the leg press, a fixed knee flexion of about 5-100 degrees and each person’s maximal range gave similar quadriceps growth after 8 weeks, with the evidence favouring no difference at the proximal, central and distal sites (Larsen et al., 2025).
• Long-length isometrics. In 23 resistance-trained people over 6 weeks, isometric knee extensions at long muscle length and full-range isotonic extensions produced similar overall quad growth. The proximal anterior thigh leaned toward isometrics, but the authors say the uncertainty precludes a firm conclusion (Varovic et al., 2025).
• Curls. As above, no regional difference between two shoulder positions.

Why might studies disagree? Short durations (6-10 weeks), small samples, different muscles measured at different sites, mostly young men, and a mix of trained and untrained participants. Untrained people tend to grow quickly from most reasonable programs, which can blur small regional differences. Trained lifters have less room to grow quickly, so effects may need more time to show.

Can you grow the inner chest, lower biceps or lower abs?

Not in the way gym slang implies. Terms like “inner chest” or “lower biceps” describe how a muscle looks, not separately controlled muscles. I did not find an imaging trial settling chest regions, and the biceps trial above found similar growth across the proximal, mid and distal sites regardless of shoulder angle.

What the evidence does allow:

• Different exercises can change which parts of a muscle grow more (quads, triceps).
• Shifting an angle probably changes the emphasis, not the on/off state.
• Some muscles show distal-versus-proximal differences depending on training length.

Think of it as steering, not sniping. For the chest, our guide to incline versus flat bench goes through what the pressing angle research does and does not show.

Compartments, pennation and what they mean for you

Large muscles are not uniform blocks. Fibres run at different angles in different areas, and some muscles are built from several parts. That architecture is one reason the same exercise can load one area differently from another.

For you, the takeaway is practical. Multi-headed muscles like the quads, triceps and hamstrings are where most of the regional and exercise-comparison research has been done so far, and where pairing two exercises has the clearest rationale. For the triceps, we cover this in overhead versus neutral triceps long head training, and for the hamstrings in seated versus lying leg curls.

For muscles that cross two joints, our sibling article on active versus passive insufficiency in biarticular muscles explains why the same muscle behaves so differently depending on the joint positions.

How to pair exercises so the whole muscle gets trained

Here is a simple approach that does not require imaging equipment.

1. Pick one main lift per muscle. Something you can load progressively, take close to failure, and move through a good range.
2. Add a second exercise with a different joint position. For the quads, that is a leg extension next to a squat or leg press. For the triceps, an overhead extension next to a pushdown. For the biceps, an incline or preacher curl next to a standard one.
3. Rotate within reason. Swap an accessory every 6-8 weeks if you are bored or a joint complains, but not every session.
4. Count hard sets, not exercises. Total weekly hard sets per muscle matter more than how many exercise names you stack. Use the training volume calculator to sanity-check yours.

A quick comparison of what the evidence supports

Muscle	Imaging evidence of uneven growth	Evidence that exercise choice changes the pattern
Triceps	MRI: regions with higher activation grew more	Limited; mostly one multijoint exercise studied
Quadriceps	Ultrasound and RCT data	Stronger: leg extension versus squat differed
Biceps	Similar growth across regions	Not seen between preacher and Bayesian curls
Quadriceps, trained (leg press)	Growth at all sites in both conditions	Not seen between two ranges of motion

What about people who are not in the gym every day?

If you train three or four times a week on a budget, in a crowded Indian gym with limited machines, you do not need a full machine floor to apply this. A barbell or dumbbells, one cable or a leg extension machine, and a bench cover most pairings. The principle is two angles per muscle, not a perfect equipment list.

Training hard matters more than the exact exercise. Eating enough protein (dal, paneer, curd, soya, eggs or chicken, whatever fits your diet) and sleeping properly will move the needle more than choosing between two curl variations.

When to see a doctor

Normal soreness is expected. Sharp pain in a stretched position, joint pain that persists for days, swelling, numbness or a pop followed by weakness are not signs of region targeting. They are reasons to stop and get assessed by a doctor or physiotherapist before you keep loading that position.

The bottom line

Muscles grow unevenly, and imaging proves it. The practical lesson is modest: use two sensible exercises per muscle that load it differently, train them hard through a full range, and keep your weekly volume honest. Do not expect to hand-pick the lower biceps or the inner chest.

Most of this research is short, in young men and in a handful of muscles. If a study contradicts a gym belief, trust the pattern across several studies, not one headline. And if you want a ready-made structure, start with our free workout plans and adjust from there.