he's talking about range of motion, not variety of exercise. He's right - when you do static training, you will only gain strength in the static position that you are holding. Not only that, but the resistance is still not entirely progressive. I can put my hands in a prayer position and push them together. That will work my pecs and tris. However, I can only offer so much resistance... If I could forever increase it, then the pressure would eventually become too great and I would break my own hands...
same thing with mungbean's examples. pushing a house isn't progressive resistance - it's the same weight every single time. your body will get used to pushing against that weight. Once you press against it for so many minutes, it becomes an endurance exercise. That's not making you stronger anymore. If it was, then you would eventually be able to actually move the house - and that ain't gonna happen.
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