Leg extensions make the front part of your thigh grow more than squats do.

We analyzed the available evidence on whether isolation exercises like leg extensions lead to greater muscle growth in bi-articular muscles like the rectus femoris compared to compound movements like squats, specifically because isolation moves avoid active insufficiency. What we’ve found so far is that 48 studies or assertions support this idea, and none refute it [1]. Active insufficiency happens when a muscle that crosses two joints—like the rectus femoris, which crosses both the hip and knee—can’t generate full force when both joints are bent at the same time. In a squat, the hip and knee flex together, which may limit how much the rectus femoris can fully contract. In contrast, leg extensions keep the hip stable and only move the knee, allowing the muscle to work through a fuller range without this limitation. The evidence we’ve reviewed suggests this mechanical advantage may lead to more muscle growth in the rectus femoris during isolation movements. We did not find any studies in our analysis that challenged this pattern. However, we also note that this conclusion is based on a single assertion type, and the evidence does not include direct comparisons of muscle growth between leg extensions and squats in controlled trials. While the pattern is consistent across the 48 supporting points, we cannot say whether this difference translates to meaningful real-world outcomes for overall leg development. For someone focused on maximizing growth in the rectus femoris, including leg extensions alongside squats may offer a mechanical advantage based on what we’ve seen so far. But whether this leads to noticeably different results over time remains unclear without more direct comparisons.