These are all great points, but one related subject you didn’t touch on is the elastic component to tendons and muscles.

If a set is done rather quickly with lighter weight, you can say the force used to lift the weight is equal to a slower heavier set, but the question arises as to where the force is coming from. You said muscle contraction governs all movement, and largely this is true, but not universally.

I’m sure you already know this, but I’ll recap it for completeness. When a muscle is stretched, elastic energy is stored within the muscle and the tendon. If reps are done quickly without enough pause at the bottom to dissipate this stored energy, then the next rep is mostly elastic action due to the stretch-reflex property of muscle (some experts suggest it may take up to 9 seconds to dissipate the energy completely). This is why guys with tiny calves can often be seen using way to much weight on calf raises and why kangaroos can hop for a long time without huge calf muscles. In both situations the tendons are doing most of the work through storing elastic energy.

So although the force may be equal, less force is being created by the muscles if the switch between the eccentric and concentric is too short (which it often is in lifters who train explosively), and therefore there is less of a growth/strength stimulus.

Also, it is true that momentum exists in any lift, but know that for any given weight, a faster concentric speed will created larger momentum (p=mv) and therefore diminish force in the muscle at the top of the rep (and the following eccentric portion if the switch between concentric and eccentric is too short to dissipate momentum – again which it usually is in lifters that train explosively).

Of course experienced lifters can train explosively in a fashion that solves these two problems and allows what you wrote to work very well. All in all good article though, I enjoyed it.