Sit ups and crunches are one of the most unproductive exercises you can do to work your core. If you think about the most important functions of the core muscles you’ll likely end up with these 2 answers:
- Stabilize and protect the spine from excessive movement
- Force transfer from the lower body to the upper body
That being said, you can now appreciate why exercises that encourage motion at the spine are not the most productive ones when you want to work your core for functional and sports performance purposes. That’s why exercises such as planks, belly presses, and chops and lifts variations are far better options.
But what if sit ups and crunches actually served a purpose?
Before you ask, no, I’m not crazy.
One of the big differences between exercises that recruit your trunk muscles isometrically (planks, etc), and crunches and sit ups is the shortening of the muscles during the exercise.
If you perform too many crunches and sit ups, there is a c0ncetric action on the rectus abdominis that will most likely shorten the muscle in the long run. Because of the rectus’ attachment on the ribcage, it might pull you into a bigger kyphosis.
The guy probably did too many crunches…
What might be beneficial with these exercises might be more in regards to the oblique muscles. During a sit up or a crunch, the obliques pull the lower ribs down via their upper attachment, and posteriorly tilt the pelvis via their lower attachment on the illiac crest.
For somebody who presents with a significant rib flare and an anterior pelvic tilt, it might not be a bad idea to include a low volume of these “evil” exercises with a rehab purpose to correct the issue. We’re not talking about doing 100′s of crunches per day here.
This really is the only situation in which I might consider using a couple sets here and there with an athlete, though.
For this purpose, I like the straight leg sit ups for the way it recruits the internal and external oblique.
But again, this is something I would use only for rehab or prehab purposes, and the bulk of my core work would still be variations of planks, belly presses, un-even carries, etc.
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