I have a confession. I can't do a sit up. I mean, I can do a sit up. But, it is either reeeaallllyyyy slow, or involves some pretty aggressive arm flailing. You know, like way up over you head and then....wooosh...throw your arms forward until you are upright...?? I can usually hide my lack of sit up ability, but I was totally exposed in a Core class that I took the other day. The goal of the exercise that I utterly failed at was to lie with your feet on the ground, knees bent, and crunch up until your shoulders and upper ribs were off the floor. I got my shoulders up, and then was 100% stuck. Despite the ridiculous amount of effort my poor abs were putting in, my torso was not curling up any further.
Not. Having. It.
You know what I blame (besides my utter lack of commitment to actually practicing situps)? Crunches.
I grew up in the generation of "core training" and "don't do sit ups, they'll hurt your back". Well, guess what? The era of curling only your upper body up off the floor did more damage than good (despite all of the beautiful pictures out there of men and women with six-packs in a semi-crunch pose...). I did crunches for pretty much all of my adolescence through my 20's. Now I have a strong abs and my back hurts and I can't do a sit up. (Be honest. Can you? Without help of any kind? Knees bent...just sit up. Try it.)
If you can, well done. You're amazing. (Seriously) And one of very few. If you can't, you're probably like me. A victim of the crunch.
Why has the crunch (i.e. "core training") led to such a huge problem? Because it wasn't training the right muscles. Well, at least it wasn't training all of them. Of course your abdominal muscles are important to be able to do a sit up, but you know what's more important? Your iliospoas - a.k.a your hip flexors.
(There are others, of course...your hips are complex...but we're going to stick with the biggie for now).
Your iliospoas, or hip flexor, is a pairing of two muscles - the iliacus and the psoas. They connect your low back (T12-L5) to the front of your femur bone. When the iliospoas contracts, your leg goes up, or flexes. If you don't actively use them, they get tight and weak. It's actually pretty easy to let this happen, because your quads also flex your thigh. So, if you have strong leg muscles, you can compensate for weak hip flexors. This is what happened to me.
How can you tell if you have weak hip flexors? Two pretty obvious ways. 1) If, when you are standing upright, your butt sticks out behind you and your low back arches, you most likely have weak/tight hip flexors. 2) If you are pretty active but still have low back pain (although the hamstrings are often blamed) you more likely have weak/tight hip flexors.
You could also try a test. Stand up as straight as you can and pull one knee up into your chest. Let it go, and see if you can hold it up without leaning backward or letting your knee come down (you may want to do this in a mirror or get someone to watch you). If you have to lean back or your leg comes down a lot, you definitely have weak/tight hip flexors.
So, what do you do?
There are several exercises you can use to strengthen this muscle.
1) Lay on your back, one leg bent and one straight. Raise your straight leg to 90 degrees and then lower, slowly.
2) Stand up straight and bring your knee up to your chest (like you did in the above test). Let it go and hold as long as you can without leaning back. You can make it harder with a tall box like Mike Boyle does in the video below.
To get a more dynamic, explosive action from your hip flexor try these.
1) Lunge back, push off your front leg and drive the back leg forward and up into your chest (also an amazing exercise to put into a circuit).
2) Do a high knees run from one end of the room to the other, keeping your back upright (it's so hard if you have weak/tight hip flexors).
3) DO SIT UPS. (With a bent knee sit up, the iliopsoas is going to be the prime mover of hip flexion).
You should also stretch your hip flexors, but stretching alone is not going to fix the problem. You'll just a have a weak, slightly less tight hip flexor (and still be embarrassed in Core class...)