Lying Leg Curl 💡 This is probably a trickier one to get than most think. Firstly, let's take a step back and ask ourselves what is our goal? What exactly are we doing, and why? Movements: Knee flexion. Muscles: Biceps femoris (long head), semitendinosus, semimembranosus & gastrocnemius, but we're most concerned with the first 3 for now. Range: Mid - Shortened range. Example 1 in the video highlights how the exercise is typically formed. As you can see, in simple terms, Gary's ass is raising up.