Intrinsic vs. Extrinsic Musculature
This is where it begins. If you want to really understand your body’s musculoskeletal system in a way that allows you to tailor your life and your workouts in a healthful way, this first concept is essential. There are many models and ways of thinking about the body’s system of muscles, but the one I think is most useful and easily-applicable is to divide them into 2 groups: Intrinsic and Extrinsic.
Extrinsic muscles are the big guys. They’re the ones you’re trying to tone and sculpt so your tush looks good in those leggings. Examples are your gluts (butt muscles), quads (thigh muscles) in your legs or your biceps or deltoids (think Michelle Obama) in your arms. Just like any muscle, extrinsic muscles act to move a joint. When you want to walk up a stair, your brain sends an electrical impulse on the nerve highway to tell your hip flexors to fire, and the result is that your leg lifts and you place your foot on the stair. But what makes an extrinsic muscle extrinsic, is that its bulk lies relatively far away from the joint it controls. Because of that, extrinsic muscles give you the capacity for strength and power, but because of their location if they’re too bossy they can produce pretty messy motion inside the joint. Bad news for the longevity of your joints.
Intrinsic muscles, on the other hand, lie deep within the body and their bulk sits very close to the joint they control. Think the rotator cuff, or in the case of the spine, the lumbar multifidus. My absolute favorite intrinsic muscles are the iliopsoas (pronounced ill-ee-o-so-as) that lie deep within the abdomen like soldiers guarding each side of your spine. Unlike extrinsic muscles, the job of the intrinsics is to produce gorgeous, precise movement at a joint. Instead of strength and power, they give you CONTROL. Think football player (extrinsic) vs. ballet dancer (intrinsic). Why do you think football players have been known to benefit from ballet?
The intrinsics, sadly, are the oft-ignored elements of our musculoskeletal system. You often don’t isolate them in that boot camp workout or that 5-mile jog. You can’t see them so you’re not really motivated to beef them up. The fact that they’re ignored in many sports training and exercise routines is the reason I can have a big old football player shake like leaf when I make him do pilates. Just like many things in life, you don’t miss the intrinsics until they’re gone. I’ll give you an example, one I see a lot:
A patient comes to see me with shoulder pain. They’re irritated to the max, because they do HIIT workouts three times a week and run 3 miles twice a week. They drink green smoothies every morning right after they jump rope for 10 minutes and do a hundred push-up’s. They’re eating paleo, for G-d’s sake. But they remember that their Dad had terrible shoulders, so that must be the problem. I look at the shoulder. Great bulk to the biceps, the deltoid – this looks like a healthy human. But when they try to raise their arm, their shoulder blade is hiking and they can’t go beyond shoulder level. The movement looks terrible. If you want to picture what I’m talking about, think John McCain trying to wave at an audience. Didn’t look normal, right? That’s what motion looks like when your deltoid (extrinsic) is bossy and your rotator cuff (intrinsic) is not in charge.
So what do I do in a case like this? I give those deep, unappreciated intrinsic rotator cuff muscles a little love. I ask the patient to please, for the love of all that is good, STOP doing this:
and START doing something that looks a little more like this:
I have my patients work their intrinsics, which relatively speaking don’t require much weight (if any) and I insist on absolutely PERFECT form. I’m specific about these exercises, and I sit right there with my hands on the patient and make them practice until I’m satisfied they can do it correctly without me. When’s the last time your boot camp instructor or your factory farm PT did that? Hm. I’m going to be honest, people, this problem keeps me in business.
Sometimes, what I find, is that I really have to sell intrinsic exercise. It’s small. I had a patient once call the exercises I give for intrinsics “ethereal”. Ha! It’s not a bicep curl with 20 lbs. It’s lying on your back with your elbow supported, 2lb weight in your hand and rotating your arm forward and back making sure your shoulder blade stays perfectly positioned. You do that for 2 weeks and we increase to 3lbs – woohoo!!! But you know what happens ultimately? You lift your arm overhead without pain, that’s what. Then you’re with me. Then you appreciate your intrinsics. Then – and only then – can we also start to work those extrinsics.
The Movement Mama 