Under strictly controlled conditions, in experiments that have been published in the most reputable peer-reviewed physiology journals, my lab and others around the world have shown that small amounts of interval training can produce benefits we usually associate with large amounts of endurance training. The harder and faster you go, the less time your exercise requires. Go as hard as you can in short bursts, and you can get the benefits of an endurance exercise regimen with less than 5 percent of the time spent in hard exercise, 10 percent of the work expended, and only one-third of the total
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