It's crunch time

(HealthDay)—Toned abs don't just look great, they're also vital for good posture and avoiding lower back pain.

But there's a limit to how far the exercises known as crunches will go toward getting you those six-pack abs. These exercises create definition, but they won't get rid of belly fat, according to a report in The Journal of Strength and Conditioning Research.

That goal needs the one-two punch of exercise to firm muscle and diet to reduce fat. That being said, crunches belong in a core workout—that's one targeting all the muscles in your torso.

When it comes to crunches, working smarter is more important than doing hundreds of them.

To intensify ab workouts:

• Increase the number of reps per set.
• Increase the number of sets.
• Shorten resting time between sets.
• Increase the angle of exercises.
• Wear ankles weights.
• Hold a weight plate against your chest.

Here are specific pointers to improve the effectiveness of the most popular exercises.

For the basic crunch, lie on your back, knees slightly bent, feet flat on the floor and hip distance apart. Breathe in, then exhale as you tighten your abs and lift your head and shoulders toward the ceiling. Do not curl up toward your knees. Hold briefly, then slowly return to the starting position, inhaling as you lower yourself to the floor. Start with 10 reps done in good form—no jerking or rushing.

For the jack knife, lie flat with legs extended and together, and arms extended behind your head. Inhale, then exhale and bring your legs up 30 to 45 degrees from the floor as you raise your torso and swing arms parallel to your legs, hands reaching for your feet. Hold, then slowly return to start, inhaling as you lower yourself to the floor.

For your oblique muscles, lie on your right side, legs together, knees bent. Inhale, then exhale and, with your left hand behind your head, raise your left elbow toward your waist, feeling the crunch along your side. Hold, then slowly return to start, inhaling as you lower yourself to the floor. When you complete your set, switch sides.

Unlike other muscle groups, abs can be worked on a daily basis, but resist overdoing it.