On the pushup spectrum, the single-leg Swiss-ball variation is one of the toughest for three reasons: 1) your body is on a decline, increasing the amount of body weight you need to lift, 2) your load is supported by only one foot, making you unstable, and 3) your core is forced to work even harder to prevent the Swiss ball from moving forward or back, or from side to side. "The single-leg Swiss-ball pushup is brutal, and you need extreme upper-body endurance and core strength to do multiple reps in a row," says Todd Durkin, C.S.C.S., author of The IMPACT! Body Plan. Do you have what it takes to crank out rep after rep? Find out with this weekend's diabolical pushup challenge.

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Here's how it works: Do as many single-leg Swiss-ball pushups as possible for 20 seconds. Rest for 20 seconds, and then do it again with your other foot on the Swiss ball this time. Watch the video above to see Durkin and linebacker Eric Bakhtiari perform the challenge. Durkin completed 42 single-leg Swiss-ball pushups and Bakhtiari did 60. What was your score? Let us know in the comments below.

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