Question about moment arm and force. (NSCA)

[eatbigliftbig92]

I was under the impression that the longer a moment arm was, the less amount of force needed to move a certain mass.

This specific diagram has me confused as it seems to be the opposite.

Is it a mislabeled diagram?
Does the moment arm being longer and requiring less force depend on the type of lever?
Am I misinterpreting the diagram?

Thank you for your time! I look forward to learning the answer to this issue I'm having.

[KyleAaron]

Some general background to make the abstract more practical. With a crowbar, for example, since torque = force x length of lever arm, a longer crowbar makes it easier to get things moving. But in the body, muscles act close to the joint, the fulcrum in the diagram. It's like pushing a door open - push near the handle and it's easy, push near the hinge and it's harder. In the human body, the muscles are always pushing (or rather, pulling) near the hinge on the door.

Consider the knee, for example. If the hamstrings attached near the ankle, then X amount of force would produce more torque than with their attaching at the top of the tibia. But then they'd get in the way, so they attach at the top of the tibia instead. As well, muscles have the function not only of moving a joint, but stablising it just as ligaments do - and attaching closer to the joint makes it easier for them to keep the joint together than if they attached further from it.

Now the diagram. The diagram depicts a horse's leg, or similar animal. It would be easier for most to understand if it depicted a human leg. Ignoring the toes, pretend that the image is of a human leg, with the person facing to the left. The left-hand image is a lower part of a squat, the right-hand image is towards the top of the squat. Your quad, the muscle at the front of your thigh, crosses your knee and attaches to the front of your tibia, your shinbone. It has the function of extending the knee, straightening it.

When you squat, where do you feel the quad doing the most work, at the bottom of the squat or the top? That "L(bend)" moment arm could as well be the moment arm of the quad in the squat. When that moment arm is longer, more work is being done by the associated muscles - in this case, the quad. So the bottom of the squat is harder to do than the top, which is why everyone cuts it short.

This is a good example of the fact that if a person lifts for a while before they start a course like this, it'll make much more sense. The NSCA does not require this.