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Strong Support

causal

History

When performing seated leg curls with the hamstrings stretched, the long head of the biceps femoris and the semitendinosus grow 14–24% more than when trained at shorter lengths, but the short head of...

Pro

Against

Mechanism

Synthesis from 1 study

How it works

When you bend your hip during leg curls, the muscles that go across both your hip and knee get stretched more than the one that only crosses the knee. This extra stretch makes those muscles grow bigger because it creates more tension inside them. The muscle that only crosses the knee doesn't...

Most probable mechanism

In Simple Terms

When the hip is bent during leg curls, the muscles that cross both the hip and knee get stretched more than those that only cross the knee. This stretch creates more tension inside the muscle fibers during contraction, which triggers signals that tell the muscle to build more protein and grow larger. The muscle that only crosses the knee doesn't stretch as much, so it doesn't grow any more than usual.

Causal chain

Hip flexion during seated leg curl elongates biarticular hamstring muscles (biceps femoris long head and semitendinosus) beyond the length achieved during hip extension in prone position

Verified by multiple studies

which leads to

Greater muscle length increases passive tension and sarcomere strain during contraction, enhancing mechanotransduction and metabolic stress within muscle fibers

Supported by evidence

which leads to

Elevated mechanical and metabolic stimuli activate intracellular signaling pathways that increase myofibrillar protein synthesis and reduce protein breakdown

Indirect evidence only

which leads to

Net protein accretion leads to increased muscle cross-sectional area and volume specifically in biarticular hamstrings

Verified by multiple studies

Evidence from Studies

Supporting (1)

Community contributions welcome

Greater Hamstrings Muscle Hypertrophy but Similar Damage Protection after Training at Long versus Short Muscle Lengths

Randomized Controlled Trial

Human

2021 Apr 1

Contradicting (0)

Community contributions welcome

No contradicting evidence found

Gold Standard Evidence Needed

According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.

Source Study

Greater Hamstrings Muscle Hypertrophy but Similar Damage Protection after Training at Long versus Short Muscle Lengths

Score: 60

DOI: 10.1249/mss.0000000000002523

Science Topic

Does training hamstrings at longer lengths increase hypertrophy more in long head and semitendinosus than in short head?

Supported

Hamstring Length Training

We analyzed the available evidence and found that training hamstrings at longer lengths may lead to greater growth in the long head of the biceps femoris and the semitendinosus compared to the short head. Specifically, when seated leg curls are performed with the hamstrings stretched, the long head and semitendinosus show 14–24% more growth than when trained at shorter lengths, while the short head shows only about 10% growth regardless of stretch position [1]. This pattern suggests that muscle length during training might influence how much these different parts of the hamstring respond. The short head, which doesn’t cross the hip joint like the other two, may not benefit as much from being stretched in the same way. What we’ve found so far points to a possible difference in how each hamstring muscle responds to stretch-based training, but we don’t yet know if this applies to other exercises or training volumes. The evidence we’ve reviewed doesn’t show any studies contradicting this pattern, but it’s based on a single assertion with no additional data on other movements, populations, or long-term outcomes. For now, if you’re looking to target the long head and semitendinosus more, training them through a fuller range of motion — like in stretched leg curls — might be worth considering, though more research is needed to understand how consistent this effect is across different people and routines.

0 items of evidenceView full answer

Similar Assertions

Just stretching your muscle under light weight won’t make it grow — you need to push hard while it’s stretched out, like doing a bicep curl slowly at the bottom where it’s fully extended.

78%

When trained individuals exercise biarticular muscles with their joints in positions that stretch the muscles more, those muscles grow larger than when exercised in positions where the muscles are less stretched.

77%

In untrained young women, doing biceps curls with both arms at the same time or one arm at a time leads to the same amount of muscle growth in the upper arm after 8 weeks, suggesting that how much total muscle is activated during the exercise does not control how much the muscle grows.

76%

For people new to weight training, lifting weights with one arm or both arms at the same time leads to similar muscle growth, suggesting that the total amount of weight lifted matters more than whether the muscles are worked one side at a time.

74%

Working your biceps with your arms stretched back might grow the upper part of the muscle a bit more than doing curls with your arms already in front of you.

74%