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HIIT training has been around for a few years but it’s peaking now because there is more research showing how effective it is when done properly, Brown says. Only 20 minutes of intense training can bring the same result as an hour or more at the gym. Who has so much time to spare anyway these days…Davis has a preferred circuit training: 10 movements in 10 minutes; each exercise is done for 40 seconds with a 20-second break in between.