During leg extension exercises, the rectus femoris muscle grows more in response to changes in hip angle than the vastus lateralis, reflecting structural and mechanical differences between these...
Mechanism
Synthesis from 1 study
Bending the hip less during leg extensions stretches the rectus femoris muscle more because it spans two joints. This stretch makes the muscle work harder, causing it to grow bigger than the vastus lateralis, which doesn't stretch as much because it only crosses one joint.
Most probable mechanism
When the hip is bent less during leg extensions, the rectus femoris muscle gets stretched more because it crosses both the hip and knee joints. This stretch increases the force the muscle experiences during contraction, which triggers more muscle growth in that specific muscle compared to others that don't stretch as much. The vastus lateralis doesn't change much because it only crosses the knee and isn't affected by hip position.
Reduced hip flexion increases the length of the rectus femoris muscle-tendon unit due to its bi-articular anatomy crossing both the hip and knee joints
Increased muscle length during contraction elevates passive tension and enhances motor unit recruitment across the full range of motion
Elevated mechanical tension activates mechanotransduction pathways that upregulate mTOR signaling and stimulate satellite cell proliferation
Increased protein synthesis and myofibrillar accretion occur preferentially in the rectus femoris, leading to measurable thickening of muscle fibers
Evidence from Studies
Supporting (1)
Community contributions welcome
The effects of hip flexion angle on quadriceps femoris muscle hypertrophy in the leg extension exercise
Contradicting (0)
Community contributions welcome
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.