The second issue many have with the leg extension machines are that they’re bad for your knees. Instead of only using leg extensions, use them as a tool towards the end of your workouts once you’ve already completed your compound movement (such as a squat). This is because there is only a small opportunity for progressive overload (AKA a lack of ability to provide continual, increased stress on the body), which is necessary for muscle growth.

For example, if you only do quad extensions, but aren’t utilizing movements such as squat or lunge variations in order to build your quads, its very unlikely you’ll see much progress. The flak you may hear comes into play due to people utilizing machines over compound (multi-joint) movements. As already stated, when it comes to EMG activity, its been shown to be some of the most beneficial movements to isolate the quads. Leg Extensions are Useless for Building Muscle? Some of the criticisms that may come up with these machines are that they suck for building muscle and they suck for your knees. While there are some criticisms to using these machines, leg extensions are one of the best at targeting and isolating our quads.

Big quad sweep