Note that these were untrained people. I doubt a fit person would get any response at all for such a low load. Actually, once you get really fit, you want to d

Note that these were untrained people. I doubt a fit person would get any response at all for such a low load. Actually, once you get really fit, you want to decrease the high intensity. Because otherwise it increases your recovery time so much, that the amount you actually can work out is low. Almost all volume a professional endurance athlete does in addition to what a normal amateur does, is low intensity.