How How are sit-ups and crunches different?

You’ve heard that one of the best ways to prevent or correct lower back pain is by addressing the “core” muscles, by making them stronger and more resilient with various abdominal exercises. While this is generally true, certain abdominal movements, especially those under gravitational tension and resistance, for example, can cause certain types of back pain to become irritated. Let me explain the differences between the abdominal exercises and you can decide which is best for you.

The core muscles are a group of muscles that live between the chest and the hips-the front and back muscles of the trunk. Other muscles like the glutes and hamstrings, shoulder blade and neck muscles can significantly assist in the function of the trunk as well, but the “core” muscles are generally those muscles surrounding your midsection.

Two of the most common exercises for the trunk are sit-ups and crunches. Here are the differences and their advantages:

Sit-Ups: This exercise involves mounting your feet on a bar (or piece of furniture) or placing your feet on the floor, then bringing your trunk up towards your thighs. A lot of mechanical stress is placed on your lower back and sacro-iliac joints with sit-ups, and your hip flexors become the main movement generators after the halfway point point, instead of your abdominal muscles. In other words, during a sit-up, the abdominal muscles initiate trunk flexion causing your shoulder blade to lift off the floor, and approximately at the halfway point, your hip flexor muscles carry you the rest of the way.

One advantage is that you can lift more than your body weight, such as by holding a weight at your chest while doing the movement. You might even be able to do much more sit-ups than crunches because your abdominal muscles are being assisted by the hip flexors. However, if the goal is to address abdominal muscles directly, then sit-ups is much less efficient because your abdominal muscles are almost at rest, or minimally engaged, beyond the halfway point of the sit-up.

Crunches:

The main difference in crunch motion is that your feet are off the floor, unmounted and dangling free in the air. Ideally, both your knees and hips are bent to 90 degrees, but there are many variations on a theme for doing crunches. The trunk flexion, like the sit-up, is initiated by abdominal muscles. As your shoulder blades rise, at some point your arms, elbows, or even your chest will collide with your thigh muscles and the trunk flexion cannot continue, and you then bring your shoulder blades down towards the floor. This motion continues until you are tired or hit your designated repetition.

You can do about twice the number of crunches as sit-ups for the same amount of time, which is important for efficiency. The abdominal muscles are practically at rest half the time during a sit-up, and crunches eliminate this rest period-a definite advantage in efficiency! Another mechanical advantage is that the crunch eliminates much, actually nearly all of the stress on the lower spinal joints including the sacro-iliac joints!

Think of a teeter-totter. In a sit-up, your feet are one side of the teeter-totter and your neck/upper back are on the opposite end. Your lower back (spinal joints, sacro-iliac joints, and even your hip joints) are in the middle, acting as a fulcrum in a lever system. This shouldn’t be a problem if there are no injuries, bone spurs, or arthritic conditions in the lower back or hips.

But for those with chronic lower back pain, weak trunk muscles, and a history of arthritic symptoms, the sit-up will invite more problems to your core than benefiting the abdominal muscles. Choose instead crunches for this situation, and get twice the amount of work done for the same amount of time, while simultaneously reducing the stress load on your spinal joints!

You can do sit-ups for numbers or time, and beginners will benefit from a set number of repetitions. As you get in better shape, you should challenge your abdominal routine by doing them for a designated time, like 2 minutes, 4 minutes, or whatever your ability. Doing the same number of reps gets easier over time, so keep that in mind in order to constantly stimulate change. Apply the “no-pain, no-gain” theory with sensibility when doing sit-ups, and keep in mind that your situation is unique no matter the age. If you have neck pain with sit-ups or crunches, you may want to support your head with a light hand contact just behind the ears. Crunch away...carefully!

Dr. Adrian Pujayana has been providing drug-free solutions for health and wellness to adults,

athletes, and youth since 2000 through his private practice at Family Chiropractic Center of South Pasadena, a place for strength training and nutrition based health care. For comments or questions, email him at southpaschiro@gmail.com