When performing leg extensions with the hip fully extended, the rectus femoris muscle grows larger than the vastus lateralis muscle because the rectus femoris spans two joints and is stretched more...
Mechanism
Synthesis from 4 studies
Bending your hip while doing leg extensions stretches the rectus femoris muscle because it crosses both the hip and knee. This stretch makes it work harder, causing it to grow bigger. Other thigh muscles that only cross the knee don't stretch with hip position, so they don't grow more.
Most probable mechanism
When the hip is bent during leg extensions, the rectus femoris muscle gets stretched because it connects both the hip and knee. This stretch makes the muscle work harder under tension, which triggers more muscle growth. Other thigh muscles that only cross the knee don't get stretched by hip position, so they don't grow more.
Hip flexion positions the rectus femoris in a lengthened state across both the hip and knee joints during the initiation of knee extension
Increased muscle length elevates passive tension and enhances motor unit recruitment throughout the muscle's range of motion
Elevated mechanical tension activates mechanotransduction pathways that upregulate mTOR signaling and satellite cell proliferation
Increased protein synthesis and myofibrillar accretion occur specifically in the rectus femoris, resulting in measurable muscle thickening
Evidence from Studies
Supporting (2)
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Hip flexion angle affects longitudinal muscle activity of the rectus femoris in leg extension exercise
Contradicting (2)
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The effects of hip flexion angle on quadriceps femoris muscle hypertrophy in the leg extension exercise
The effects of hip flexion angle on quadriceps femoris muscle hypertrophy in the leg extension exercise
Gold Standard Evidence Needed
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