mt: Most of the movements you mentioned are natural, just not under the stress that resistance training would provide. You're correct about the leg curls though. They too are an unnatural movement to a degree but hamstring muscles do "pull up" when running so it isn't as bad as extentions.
Because any movement is a little awkward doesn't mean you can't strengten the muscles by using them. A leg curl uses body torque to a degree, which is why standing leg curl you can never use much weight. Compare that to how much weight you can squat. That's my point. If you want to build a big muscle , you need to use a heavy weight.
Nothing is written in stone. This is why I argue with people who are so opposed to the Smith machine, claiming it isn't "natural." People claim presses behind the neck aren't natural and I never had a problem with them. Hell, lifting tons of weight isn't natural! But knees are delicate. They injure easily and take forever to heal, so it's prudent to work with the bodies natural movement as opposed to forcing it to get stronger by stressing it in a compromising way.
Because any movement is a little awkward doesn't mean you can't strengten the muscles by using them. A leg curl uses body torque to a degree, which is why standing leg curl you can never use much weight. Compare that to how much weight you can squat. That's my point. If you want to build a big muscle , you need to use a heavy weight.
Nothing is written in stone. This is why I argue with people who are so opposed to the Smith machine, claiming it isn't "natural." People claim presses behind the neck aren't natural and I never had a problem with them. Hell, lifting tons of weight isn't natural! But knees are delicate. They injure easily and take forever to heal, so it's prudent to work with the bodies natural movement as opposed to forcing it to get stronger by stressing it in a compromising way.