9. Crunch
The faux pas Jerking your neck, not lifting shoulders, failing to engage abs
The facts These mistakes will result in a sore neck, and your abs won't get any firmer.

The fix Lie on your back with knees bent and feet flat on mat, hip-width apart. Place hands behind head, thumbs behind ears, fingers unclasped. Hold elbows out to the sides. Contracting abs, draw hips and lower ribs together, keeping buttocks relaxed. Without pulling on neck or drawing elbows in, curl up and forward, keeping head and neck relaxed as shoulder blades lift off mat. Hold, then slowly lower back down. Strengthens abdominals.