When's the last time you ran backward? Sure, you might not look cool doing it, but studies have found that motoring in reverse torches more calories, works your lungs more efficiently, and helps your bones to absorb shock more effectively than regular running. Give it a shot with this 400-meter forward-backward running challenge created by Todd Durkin, C.S.C.S., author of The IMPACT! Body Plan.

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Here's how it works: Sprint a quarter mile -- running forward -- as fast as possible. Rest for 2 minutes. Then, complete the quarter mile again, but run backward this time. Your goal is to finish the distance in less than double the time it took you to run it the first time.

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When Durkin ran the challenge he completed the regular sprint in 1 minute and 58 seconds. He needed to complete the lap running backward in less than 3 minutes and 56 seconds. His final time: 3 minutes and 40 seconds. What was your time? Let us know in the comments below.