Smarter Hamstring Curls with the Omnistrap?
In the smarter knee extensions Omnistrap blog we discussed basic biomechanics and focused on how using the Omnistrap lengthens the moment arm during the knee extension exercise. We are going to turn our attention back to the hamstrings and show how the Omnistrap is an effective hamstring strengthening tool and offers some advantages over other options.
As a quick review Torque = force x moment arm. That concept underpins pretty much all of biomechanics. Remember that the moment arm is the distance between the force application point and the axis of rotation. Technically it is the perpendicular distance which means it changes as a joint goes through a range of motion. To illustrate this point see the pictures below
The dotted lines in these examples are the moment arms and you can see how the higher up in the prone hamstring curl you get, the smaller the moment arm gets for the hamstring. That means the muscle has less leverage the higher up the weight is curled. You can also see how because of positioning, after a certain point gravity starts to help push the foot attachment down.
Compare that to a standing hamstring curl where you see that the moment arm for the hamstring gets larger the higher the weight is curled. In a standing hamstring curl gravity is also constantly opposing the movement.
Another factor at play in the standing hamstring curl is that the leg is free to rotate. This means the hip muscles have to work to prevent that rotation and rotation around the knee. Guess what muscle group is responsible for controlling the rotation of the knee joint. Yup, the hamstrings.