The Fastest Way to Burn Calories

Get on the rowing machine. "It literally works the entire body," says Valencia. Sprint on it for 90 seconds (approximately 250 yards), then recover for a minute. Do as many 250-yard sprints in 10 minutes as possible. Runner-up: Alternating between a full-on sprint and jog on the treadmill or outdoors. Do three one-minute sprints at 8.3, 8.5, and 9 miles per hour with two-minute jogs in between.

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