Watch Your Back: Watch Those Crunches!
While crunches are a good way to tighten your abdominal muscles, it's important to realize that every time you crunch your abs you also are crunching your back.
Traditional sit-ups and crunches place a significant of stress on your neck and lower back, with one study finding that sit-ups placed more than 670 pounds of force on the lower spine. This kind of strain can lead to bulging or herniated discs, compressed vertebrae or nerve damage.
There are excellent alternatives to develop core strength, and these options may be even more effective in helping you get those abs of steel. Instead of sit-ups or crunches, try holding yourself in a plank pose -- a high push-up position -- for a 30-second count to work your core. Once you've mastered that, try a one-arm plank to focus on your oblique muscles.