In the context of functional athletic training, core does not mean crunches. It means strengthening the stabilizer muscles around your spine and your hip and shoulder joints. Everybody has hidden core weaknesses: glutes that don't fire, setting us up for knee injuries or weak rotator cuffs that turn the bench press into a guaranteed shoulder-injury program, just to name a few. So if you're going to add one layer of complexity to your strength program, make it a few simple core-stabilization exercises. For a complete rundown of all these exercises, be sure to read 'Core Performance' by Mark Verstegen.