First, I am not a fan of sit-up testing. I don't think it tells us anything we want to know about fitness and it may be counterproductive. Dr. Stuart McGill (renowned spine biomechanist) generally advises against sit-ups because his data shows that they can be damaging. However, until we take them out of our fitness tests in the military (and I believe we will one day), you have to get them done. I have the unique opportunity to watch thousands of people do sit-ups. I also have the unique opportunity to be able to work with every one who fails the sit-up portion of the U S Naval Academy Physical Fitness Test. There aren't many as most of the Midshipmen do great. However, there are more than I had expected. Over the last couple of years I have noticed an interesting phenomenon regarding sit-up failures. 9 out of 10 people who fail the sit-up portion suffer from the same biomechanical movement pattern flaw. When we fix this flaw, they pass and never have trouble with sit-ups again. What is this flaw? Anterior pelvic tilt during the sit up. Take a look at the figure below. A is the starting position for just about everyone. As soon as the sit-up is initiated, a normal movement pattern is to roll the pelvis back (posterior pelvic tilt), engage the abdominal muscles and flex the spine. This results in a bending forward at the spine rather than the hips (B below). In about 9 out of 10 cases of sit-up failures what I observe is C below. The first thing they do is roll the pelvis forward (anterior pelvic tilt). This locks the spine in hyper-extension and prevents any forward flexion of the spine. As a result, the only way to do a sit-up at this point is to bend at the hips, rather than the spine. This is a hip flexor dominant pattern that takes the abdominals largely out of the movement. Plus, it is a much longer, and harder movement. In most cases, I see this anterior pelvic tilt pattern in their pushups as well.
How do we fix it? First we identify the issue and explain to them what they are doing. It is always an "aha!" moment. Many have stated that people were always telling them that they were doing sit-ups wrong but they couldn't say how. Many also state that sit-ups often hurt their back. Then we have them start doing feet elevated crunches with a special focus on engaging the abdominal muscles. I also have them do the old "6-inches" exercise that coach used to make you do in football practice. This one is simple. Lie on your back and hold your legs out with your heels 6 inches from the ground. Hold this position. However, in this case, roll your pelvis back into posterior pelvic tilt while you do it. Make sure that your lower back is in contact with the ground. This is a great exercise for forcing you into posterior pelvic tilt against a resistance. The legs produce a big rotational moment that tends to pull your pelvis forward. Your job is to counter that by rotating your pelvis back and holding it. We also add some planks, bird dogs, and some glute work. Then we have them practice sit-ups, focusing on a neutral or posterior tilt to the pelvis. It sometimes takes a couple of weeks to start to reprogram the sit-up but we always get there.
If you are having trouble with sit-up performance, have someone watch you do sit-ups and see if you are moving into anterior pelvic tilt. Sometimes it is subtle and hard to see, however, the lack of flexion in the spine will be most telling. If this is the case, try what we recommend above. We have not had it fail yet. ?
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