This seems like a simple movement – How to perform machine calf extensions…. However I see people doing it wrong all the time. This is not a quad exercise, this is a calf exercise. Once you extend your legs out till there is only a slight bend in your knees, you should not move your legs at all. The only pivot should be with your ankles as if you were standing up on your toes. This isolates your calf. See the below video on How to perform machine calf extensions.