Here's a great trunk exercise for you to try during your next workout. Anti-rotation exercises are excellent and I'd choose these way ahead of crunches.
How to do it:
Set yourself in a push-up position but with narrow hands and wide feet.
Hold a neutral spine position. Keep your tummy tight and squeeze your glutes.
Reach for your opposite elbow whilst trying to keep your hips completely still (they'll want to turn so don't let them!)
Start by reaching for the elbows, but to develop the exercise and make it tougher, reach for the opposite shoulder as shown in the video.
Start by trying 5 on each side, then add reps when appropriate.
By Marc Brown