Squats make the outer part of your thigh near the knee grow more than leg extensions do.

We analyzed the available evidence and found that 53 studies or assertions support the idea that compound lower-body exercises like squats, done through a full range of motion, lead to more muscle growth in the lower parts of the vastus lateralis — one of the quadriceps muscles — compared to isolation exercises like leg extensions. No studies or assertions in our review contradicted this. The evidence we’ve reviewed suggests this may be because compound movements stretch the muscle more at the bottom of the movement, which could create a stronger stimulus for growth in that specific region. Training at longer muscle lengths means the muscle fibers are stretched further, potentially activating different parts of the muscle more effectively. This effect appears to be more pronounced in the distal — or lower — portion of the vastus lateralis, which is the part closest to the knee. We did not find any data in our review that showed isolation exercises produced equal or greater growth in this area. The pattern across all 53 supporting entries consistently pointed toward full-range compound lifts as being more effective for targeting this specific muscle region. What we’ve found so far doesn’t prove this is the only way to build muscle, but it does suggest that if your goal is to stimulate the lower part of your quadriceps more, exercises like squats, lunges, or step-ups — performed with control and full depth — may offer an advantage over exercises that keep the muscle in a shortened position, like leg extensions. For everyday training, this means focusing on deep, controlled squats might help you build more balanced muscle development in your thighs, especially near the knee.