Aarg, Lee I'm having trouble visualising and trying these ones, can you just explain them again?
They were just made-up examples based on his made-up example to show a principle: if you are going to expend the energy to keep some downwind joint static (and hence not go totally floppy and collapse) while using another joint to do all the work of moving it, then why not just extend both joints as forcefully as possible, to utilize all the muscle in between? Otherwise, you just dampen your own force with your own body mass for no benefit.
The joints don't just stay at a fixed position by themselves, they use muscular force to do it (one muscle fighting against another, or if against an external object inhibiting itself partially) - so using less than the maximum voluntary force, or inhibiting the expression of that by freezing the joint rigid is bad resource management.
If it's a unifying principle for efficient movement of the whole body, then it should carry down to any joint(s) you look at. I think any small example should embody the entire principle, rather than just something kinda sorta maybe like it. In this case it was the joints of the wrist and arm, but could just as well be the toes, the fingers, the rotator cuff of the shoulder, the hip joint, the knee joint, the ankle joint, the neck, and onward ad nauseum.
Or to quote Neuromechanics of Human Movement - Third Edition, Roger M. Enoka, p102
Because the human body does not behave as a single rigid body, such as the bat, it is necessary to consider the motion of each body segment when calculating angular momentum. This requires a linked-system analysis, in which we calculate the angular momentum of each segment about its CM [center of mass] (local angular momentum) and then determine the angular momentum of the CM for each segment about the system (whole body) CM (remote angular momentum).
And that's just an introduction. There's a whole chapter on JUST how to calculate the combination of torques exerted by a system of joints. (That book is awesome.)
If you look at sports like weightlifting and powerlifting, they are entirely based off this principle. A strong snatch is not just generated by the hips, nor a strong bench press just generated by the chest (which can incidentally involve everything down to the legs), nor a strong squat just generated by the legs.
I don't think martially applicable strength need operate on wildly different principles from athletic strength, other than needing to operate at shorter time scales, with more agility, and with emphasis on generating force out from anywhere to anywhere. I used to think they were very different, but someone gave me some powerful illustration that they aren't so different as I thought.