The Hardest Ab Workouts

Getting those flat, well-defined abs presents one of the most unique challenges in fitness; not only do you have to keep body fat to a minimum with a balanced diet and regular cardiovascular exercise, but you also have to build lean muscle via strength-training workouts. If you've reached your plateau for ab-toning staples such as the crunch and hanging leg raise, you may need more challenging variations to engage your core. While there is no hard-and-fast definition of what makes an ab workout the hardest, recommendations from fitness professionals help separate some exercises from the pack.

Crunch Variations

Clark Bartram, professional fitness model and personal trainer, recommends the surrender situp. For this variation, keep your arms above your head with your feet flat on the floor. Bring your torso up as far as you can without lifting your feet and return to the starting position. Bartram and the American Council on Exercise (ACE) also recommend exercise ball crunches to amplify the intensity and effectiveness of this classic exercise. For the upper abs, NASM Certified Personal Trainer Jonathan Deprospo calls decline crunches, performed on a bench at a roughly 30-degree decline, the “hardest exercise for the upper abs.” To further heighten the challenge, perform these crunch variations while holding weight plates to your chest.

Body Weight Exercises

No discussion of challenging ab exercises is complete without mention of side planks and mountain climbers, which rank first and second on certified strength and conditioning specialist and “Men's Fitness” magazine consultant Craig Ballantyne's list of the top five killer body-weight exercises for abs. While side planks look simple to perform, they engage the obliques intensely. Mountain climbers target the rectus and transverse abdominis, but they engage muscle groups as diverse as the glutes, quads, hamstrings, lats, deltoids and obliques.

Hanging Body Weight Exercises

Hanging leg raises serve as a standby exercise for advanced crunch training – Deprospo calls them the toughest exercise for the lower abs. To make this ab-busting staple more challenging, add ankle weights or modify the movement to engage your hip flexors for a leg-hip raise. For this variation, bend your body at the hips and knees so your knees come as close to contacting your chest as possible. To take it a step further, try a straight-legged variation. According to ACE, the Captain's Chair hanging leg raise generates a higher mean percentage of muscle activity in the obliques than any other abdominal exercise.

Others

While the Captain's Chair challenges the obliques, the same ACE study finds that the bicycle maneuver, an equipment-free exercise, generates more muscle activity in the rectus abdominis than any other ab exercise. If you have a partner, the “CrossFit Journal” names the medicine ball situp throw the “toughest ab exercise ever.” This difficult workout requires two partners to perform synchronized situps while throwing and catching a medicine ball between them.