If you do leg extensions while leaning back, it might build more muscle in the top part of your front thigh compared to doing them upright.
Evidence from Studies
Supporting (0)
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Contradicting (2)
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The effects of hip flexion angle on quadriceps femoris muscle hypertrophy in the leg extension exercise
The study found that doing leg extensions with a more stretched rectus femoris (by keeping the hips less bent) led to more muscle growth. This goes against the idea that leaning back even more would help—it already tested a stretched position and found it worked best.
Hip flexion angle affects longitudinal muscle activity of the rectus femoris in leg extension exercise
The study looked at how different hip angles during leg extensions affect muscle activation, and found more activation in the front thigh muscle when the hip was less bent. But it didn’t test the exact 'leaning back' method the claim talks about, so it doesn’t fully support it.
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