Over the winter, I remember reading a couple of cyclocross race reports, several of which included complaints of back pain. And since a lot of the problems in cyclocross riders will cross over into spinning class participants (if not necessarily to triathletes), it's time to address the issue of (dramatic pause) . . .
Wait. The Pso-what?
You may have heard of this muscle. Or you may have heard the term iliopsoas, which is a combination of the iliacus and the psoas major (not the same muscles, but close enough that there's a combined term for them). The psoas is a deep hip flexor, and acts to raise and externally rotate the leg at the hip. Know what activities involve frequent frequent flexion at the hip (and external rotation, if you have something wonky going on with your form). Yep. If you're a cyclist, a runner, a stair-stepper, an elliptical-user, or (I assume) a cross-country skier--in short, if you do cardio on the land--I can almost guarantee that your psoas are tight.
And the psoas originates at the spine; it's attached directly to your vertebrae (from T12 to L4). So when it's tight (or shortened, for example when you're sitting), know what it does? That's right. Cranks that lumbar spine forward! So if you've got one of those crappy jobs that requires you to sit at a desk all day, the psoas is constantly shortened. And if that job happens to entail a long commute (look down at your legs next time you're driving; are they flexed and externally rotated at the hips?) AND you're a cardio person? Yeah, you're pretty much screwed.
We've talked about the psoas before; it figures prominently into the anterior pelvic tilt associated with swayback (lower-crossed posture). It's not the only muscle acting on that posture, but it definitely contributes. And if you drive a lot, sit all the time, and are an avid biker (or runner, or both), it stands to reason that psoas tightness might be acting on your whole lumbo-pelvic area pretty powerfully.
But what does that have to do with this searing pain in my back?
Back pain related to tightness in the psoas usually presents as pain or pressure in the low back somewhere (or possibly everywhere) from the low middle back to the tailbone, off to the side (the pain is almost never right in the midline--that is, directly on the spine, 2). It might be relieved by sitting or laying with the knees bent (later I'll show you a position in which you can lay that--in my opinion--offers instant relief).
There are nerves all up in the psoas; the origins of the femoral nerve (which is the main lower-body nerve of the front, the sciatic nerve being the main nerve on the posterior side) are "invested within [the] psoas" (3). And the femoral nerve itself emerges between the iliacus and the psoas, so overactivity of the latter can cause compression (read: PAIN) of that nerve.
Keep in mind, though, that overactivity of the psoas isn't the only cause of back pain. So if you're getting constant pain, stabbing pain, or shooting pain down your back, you should go get your back checked out by a legitimate medical professional (FYI, I'm not one). But most of the exercises I'll recommend for you here are the kinds of things that won't hurt, might help, so you may as well give 'em a shot.
Yeah, yeah. Shut up with the stupid anatomy and tell me why I hurt!
Your back hurts when you bike because you're not stabilizing properly with your core. You're yanking up on the backside of the pedal stroke using the hip flexors (PSOAS!) and you're cranking down on the front half with help from your quadratus lumborem (remember that guy?). Those muscles are working to push power down to the pedals and stabilize against each other. Without sufficient stabilization from your core musculature, and without the help of other important muscle groups (particularly the glutes), you're going to be left with one cranky body. Or that's my operating theory, anyway.
This effect is going to be particularly pronounced in cyclocross. You're doing all you can to push maximum power at several points in a cyclocross race, and that power is coming from some touchy areas--namely the hips and back. And when you're riding over rough terrain, as on a cyclocross course, the ground is too choppy to allow for the kind of smooth, even pedal stroke for which we all strive on our road/tri bikes. So you're more likely to yank up/pound down on the pedals, overworking the hip flexors and back while the quads/glutes get a free(ish) ride.
Other times you're likely to pedal like that (and so make your psoas and back hate your stinking guts)? Spinning classes, when you crank the resistance really hard. Going up big climbs. And pushing too big a gear.
So what can I do about it?
Ah, we come to the heart of the matter. Key thing is to stretch your psoas. Strengthening the glutes and core (the psoas is connected to the pelvic floor, inner thighs, and quads by fascia, 3) also helps. Yoga has done wonders for me in both regards (but keep in mind that the benefit you get from yoga depends greatly on your instructor). Here are some ideas that I think will help you:
Ahhhhh . . . No seriously. Try it. Lay on your back with your knees bent and your feet greater than hip width apart. Then let your knees collapse in towards each other. Hip flexion and internal rotation. Say it with me now: Ahhhhh . . .
Low lunge series (I)
One of the best, but it takes a good amount of concentration to get it right. Start on all fours. Bring your right foot up between your hands, and sit straight up. You should be in a knee-down lunge. If you're having trouble not falling over, do this lunge next to a wall, so you have something to hold onto. Make sure that your knee is right over your ankle; if it's pushing past your ankle (i.e. your knee is forming a less-than-90* angle), wiggle your foot forward a little further. Hips should be level and square to the front.
Now assuming you have your balance here, put both hands on the front leg and use them to push your upper body up, making your back as straight and as long as you can. Chest lifted. Shoulders back. Now sink down into your hips, bringing your right bum forward and closer to the floor. Keep your hips level. Keep your hips square. Just let gravity pull your hips lower and lower. Bonus points if you squeeze your right butt cheek. If you can stand it, stay here for a minute on each side. You can repeat this one a couple times.
Low lunge series (II)
You've done both sides with the first lunge. You're back to having your right leg forward, left knee down. Wiggle your right foot off to the side, so it's out wider than your right hip, and turn your foot out to the side (externally rotate your hip). So your knee is right over your ankle and pointing out to the side. Now lower your upper body down towards the floor and see if you can bring your hands to the floor. How about your forearms? See if you can wiggle your left leg a little bit farther back, so that you're more on your thigh than your knee. Sink your hips down. Breathe.
Low lunge series (III)
If you want to take that stretch a little further, stretch your left heel back and raise your knee without letting your hips come up. Sink your hips towards the floor. Breathe.
References and Further Reading
Source 1: The Psoas: Is it Killing Your Back?
Source 2: The Psoas Syndrome
Source 3: The functional anatomy of the iliopsoas muscle and its implications to hip and back injury in dancers
Source 4: Yoga Anatomy - Release Your Psoas