• Lie face-up with Bosu under lower back
• Keep shoulders and feet off ground
• Hold 2-4 pound medicine ball in both hands with arms extended overhead
• Perform crunch while pulling knees toward chest and bringing med ball toward knees
• Perform 8 reps on each side twice, with 60-75 seconds of rest

Kawahara: Because the Bosu is dome-shaped, it exaggerates any movement Justin makes; he can tip off or lose his balance very easily. So, he has to be a lot more reactionary—by reading and responding to the environment, which really works his core. The dome forces him to work his upper abs to keep his back from rounding over the Bosu and his lower abs to keep his hips up, so he’s working very hard before he even starts the crunch.