Hopefully with my limited knowledge of physics I can make this make sense, and please correct me if I'm mis-using any terms. What I am trying to figure out at least a rudimentary model or explanation for is how "work" peformed by the human body varies based on efficiency for the same "work". For my first example, simply standing in place, you are not doing work by the physics definition because there is no motion. HOWEVER, obviously the muscles are doing work (using energy) to stand there. Bend your knees to about 90 degrees, and then stand there--again no "work" by the physics definition because you're not moving, but your muscles are at a much higher level of exertion and "working" awfully hard to keep you there. So with no "work" being done external to the body, there is a huge difference in work being done by the muscles. I guess let me back up and ask this--is quantifying muscular "work" essentially reverse engineered by energy usage? So where I'm ultimately headed is that lifing 100lb barbell 1 meter off the floor is a fixed workload from a physics standpoint. But from a biological standpoint, accomplishing this work can cover a spectrum of muscular (not to mention cardiovascular) "work" based on various body angles and muscle recruitment. Any fatal flaws here? Anyone got easy way to speak to the difference between the external work accomplished (lifting the weight) vs. internal work (energy expendature)?