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.

We analyzed the available evidence on whether training the rectus femoris in a lengthened position leads to more muscle growth in the upper part of the muscle, and what we’ve found so far does not support this idea. There are no studies that show doing leg extensions while leaning back builds more muscle in the upper front thigh compared to doing them upright. In fact, 54 assertions directly contradict this claim, finding no meaningful difference in muscle growth based on body position during the exercise [1]. The rectus femoris is one of the four quadriceps muscles and crosses both the hip and knee joints. Some have suggested that positioning the body to stretch this muscle more — like leaning back during leg extensions — might create better conditions for growth in its upper portion. But our review of the evidence shows no consistent pattern or measurement to back this up. The 54 refuting assertions include analyses of muscle activation, ultrasound imaging, and muscle thickness changes across different training positions, and none found a clear advantage for the lengthened position. We don’t have enough high-quality studies to say whether this approach has any benefit at all, but the current body of evidence leans strongly against it. The idea that leaning back during leg extensions targets the upper rectus femoris more effectively appears to be based on theory rather than observed results. In practical terms, if you’re doing leg extensions, focus on consistent form, controlled movement, and progressive overload — where you gradually increase the weight or reps over time. Where you lean during the exercise doesn’t seem to change which part of the muscle grows, based on what we’ve reviewed so far.