When discussing six-pack abs and a toned belly, crunches often spring to mind before any other exercise. While it takes more than crunches to get a defined stomach -- you'll need a balanced diet and regular cardiovascular exercise as well -- this classic exercise continues to serve its traditional tummy-flattening purpose. As crunches help strengthen your core, they produce functional benefits in addition to aesthetic perks.
Muscles Worked
Crunches chiefly serve to tone, define and strengthen the abdominal -- or “core” -- muscles. As such, this exercise squarely targets the rectus abdominis -- the two parallel muscles that run down the abdomen -- and the transverse abdominis, an inner layer of stomach muscles that help stabilize the spine. Crunches also engage the obliques, the muscles that run down the sides of the torso, as synergists.
Core Benefits
As a core-training exercise, crunches help improve your balance by strengthening your abdominal muscles. Strong core muscles improve your posture, which helps you function efficiently in everyday life and in sporting events. A healthy posture also helps prevent lower back pain and muscle injury. A 2009 study conducted by Barry University found that runners who underwent six weeks of core-training exercises significantly lowered their 5-kilometer run times.
Calories Burned
In addition to toning, performing crunches burns a few calories. For a 160-pound person, 10 minutes of moderate crunches burns 54 calories, while 10 minutes of vigorous crunches burns 98 calories. This number jumps to 65 and 116 calories, respectively, for a 190-pound person. While a half hour of crunches could potentially burn a whopping 300 calories, fitness experts recommend small amounts of crunches – about three sets of 12 -- performed at a slow, controlled pace rather than many quickly performed crunches.
Variations
The American Council on Exercise and the Biomechanics Lab at San Diego State University find the stability ball crunch, vertical leg crunch and long arm crunch the most beneficial crunch variations for producing activity in the rectus abdominis. These exercises score electromyogram values -- a measurement of electrical activity generated by muscle contractions -- of 139, 129 and 119 percent, compared to the still-effective 100 percent EMG value of the standard crunch. For toning the obliques, the reverse crunch takes the cake with an EMG value of 240 percent.
Considerations
You'll only reap the benefits of crunches with proper form. For standard crunches, the American Council on Exercise recommends the bent-knee style; seek supervision from a certified trainer to make sure you're exercising properly. The most effective abdominal regimen includes a variety of core workouts, such as crunches, planks, stability ball crunches, roll-outs, hanging knee raises and others.