A solid core is key to both smooth, strong paddling and to stability on a board. Dave claims that a fit man should try to complete 500 crunches per session. He also says that over 100 of any kind "gets boring," so mix it up. Try the bicycle crunch.
Lay on your back with your knees up and your calves parallel to the floor. Bring your left elbow to your right knee, and then your right elbow to your left knee. Focus on tensing your core to execute the reach, not your neck. "I'll go right elbow to left knee but then I'll hold it for a count of three, so I have to engage one side for a few seconds, and then go to the other side," says Kalama. "It's not as many, but ultimately, it's probably equal to doing 50."