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The question of how little exercise is needed for the beneficial effects was asked scientifically by Arthur Jones, inventor of the Nautlius workout equipment. It was further refined by bodybuilder Mike Mentzer who was a Jones acolyte. The books Body by Science and Congruent Exercise is a relatively up to date compilation of what Jones observed over his career.
Also, the concept of intervals was made popular by a Japanese researcher named Tabata, who observed that anaerobic training improved aerobic capacity, whereas aerobic training did not improve anaerobic capacity. That is, anaerobic metabolism drives aerobic metabolism.