The lying (supine) single-leg extension is an effective way to isolate the rectus femoris, especially when performed on your back with the hip extended. Unlike the traditional seated leg extension, where hips are flexed at 90 degrees, lying flat reduces hip flexion, enhancing rectus femoris activation.

Research suggests that with reduced hip flexion, the rectus femoris experiences greater muscle engagement, allowing for effective muscle stimulation. Performing this exercise one leg at a time also helps correct imbalances and focus on neuromuscular control.

The lying single-leg extension is an excellent addition for those targeting quad growth while addressing any asymmetries in strength or muscle activation between sides.