When a muscle crosses two joints, stretching it at one joint makes it longer overall, which can make it grow more when you exercise it.
Scientific Claim
Exercises that position biarticulate muscles at longer lengths (via joint angle manipulation) produce greater hypertrophy in those biarticulate muscle heads compared to exercises that place them at shorter lengths.
Original Statement
“Bioticular muscles cross over two joints. And here are the main biotic muscles most of us care about. Different exercises can involve different joint positions such that some exercises are going to train biotic muscles at a longer muscle length than others. Take a seated leg curl and a lying leg curl. Both of these exercises have us flex our knees. However, the seated leg curl has our hip joint flexed at approximately 90° while the lying leg curl involves virtually no hip flexion. Three of the four hamstring heads are biotic and are consequently lengthened more with hip flexion. Thus, seated leg curls train the biotic hamstring muscles at a longer muscle length.”
Context Details
Domain
exercise
Population
human
Subject
training of biarticulate muscles via joint positioning that elongates them
Action
produces
Target
greater hypertrophy in biarticulate muscle heads compared to shorter-length conditions
Intervention Details
Evidence from Studies
Supporting (1)
Joint angle-specific neuromuscular time course of recovery after isometric resistance exercise at shorter and longer muscle lengths
This study found that when muscles are stretched more during exercise (like bending your knee more), they work harder — and working harder like this is how muscles grow bigger over time. So even though it didn’t measure muscle growth directly, it shows the right conditions for it.
Contradicting (1)
Does Muscle Length Influence Regional Hypertrophy? A Systematic Review and Meta-Analysis
The study found that doing exercises that stretch muscles more doesn’t make those muscles grow bigger than exercises that keep them more relaxed — so stretching muscles more during workouts doesn’t give you extra muscle growth.