Whenever possible, add resistance to your ab exercises with weight. Most people increase the load on exercises for major muscle groups but they don't on ab exercises. That's a mistake. Think ankle weights for leg raises or a 45-pound plate for crunches as shown here.
related posts
Building the Case for Hybrid Training
Bodybuilding guru Scott Abel says that training for hypertrophy, size, thickness, density, and shape is not the same as strength training. If the question is how to gain unadulterated muscle mass, is hybrid training the answer?
Contrast Training for Strength, Size, and Power
Teach your body some new tricks with these exercise pairs that combine strength with explosive power.
Tip: Build Walnut-Cracking Glutes
Here's a simple way get more glute work out of your staple strength lifts.
The Absolute Best and Worst Therapy Methods
Four of these rehab methods are great... and two are wasting your money. Here's what works and what doesn't. Bonus: Videos of the best techniques!