What makes muscles STRONG or WEAK? The answer is not quite as simple as your genetics, your activity level or how much iron you pump. We’re going to dive into a concept called the LENGTH-TENSION RELATIONSHIP, which is among the basic foundational concepts I see as integral to understanding and alleviating your orthopedic pain. As usual, we’re going to look at the underlying anatomy and then we’ll zoom out to take a more big picture look at how this concept applies to our bodies.
At a microscopic level, muscles are composed of small units, called muscle fibers, that are lined up like spaghetti noodles right next to each other in bundles:
Muscle fibers are inherently elastic, meaning they can lengthen and shorten, and that elasticity is what allows them to move your joints. Each muscle has a rich nerve supply, basically the electrical charge that causes the muscle to contract or relax. In a nutshell, your brain says “I’m about to move my finger, the nerve to your finger muscles fires an electrical current that causes the muscles to contract and your finger moves. Presto! The speed of that impulse is pretty mind-blowing. And think about how many muscles are involved in a complex movement – like walking – and it becomes even more impressive.
When a muscle shortens, we call that a CONcentric contraction. As you go up a stair, your thigh muscle (quad) shortens in order to lift you up. Equally important, though, is a muscle’s ability to lengthen in a controlled way. We call that an ECcentric (ee-centric) contraction. Eccentric contractions are important for going DOWN the stairs – your thigh muscle (quad) lengthens at just the right speed to control your body as it lowers so you don’t fall on your face.
So here’s the concept I really want to get across: the LENGTH-TENSION relationship. What that means in a nutshell is that muscles have a length at which they can produce the most tension (strength). Outside of that ideal length -when a muscle is either too long or too short- it has a harder time producing an effective contraction. And here’s why that should matter to you: the way we align ourselves has a huge effect on whether or not our muscles are able to do what they’re meant to do. I’m going to use an extreme example to illustrate this point: the backbend. The thick red line on the figure below illustrates the length of the abdominal wall muscles.
It’s not hard to see in this photo how this person’s abdominals have been lengthened in comparison to how they would have been with her standing up straight. They’re stretched, in other words. And from that stretched position, it’s pretty hard for them to generate the strength (tension) to get her back upright!
A more common, but also more subtle, example of this would be the swayback posture I talked about in my “The truth about POSTURE” post. Again, we define swayback as standing with the shoulders behind the hips:
This man is, effectively, standing in the tiniest little backbend all the time. As a result of that, his abdominal wall muscles are WEAK solely as a function of their LENGTH! Over time, that length change sets in – like stretching a rubber band and holding it in a stretched position over time, that rubber band starts to get saggy baggy. His abdominal wall muscles are going to struggle in this position to hold him up – they’re fighting a losing battle that will end in compression and pain in his low back. Add to that an additional abdominal wall lengthening force in the form of pregnancy or abdominal obesity and you can imagine how disturbed that length-tension relationship might become!
The same is true if a muscle is too SHORT. Let’s look back at the backbend example, but this time the thick red line represents the gluts (butt) muscles:
Relative to his standing position, the length of this man’s glut muscles are actually shorter here. And, because they are shorter than they prefer to be, they’re also weak. In the example of our swayback man, again the more common but less extreme situation, those short gluts are going to be inherently weak and they also are going to contribute to the compression in this poor guy’s back.
The very first thing I do with my patients after I evaluate them is talk about their specific alignment and movement habits, and what muscles are SHORT and LONG based on those habits. The same length-tension relationship issues that I just described can be extrapolated to absolutely any muscle in the body based on the positions we habitually put them in. I educate patients that changing their postural and alignment habits will immediately put their muscles in a better position to succeed – and success means stable joints. And stable joints are happy joints that don’t hurt.
An important point to make is that there is great value in sitting down with someone like me – a physical therapist (PT) – and really looking at your pain situation from an alignment, movement and length-tension perspective. It’s hard to guess at this yourself. And if you’re already seeing a PT but you haven’t really been given solid education or cuing on alignment or movement corrections, you need to start asking some questions or find another practitioner.
I stopped scolding patients for not doing their exercises as soon as I became a parent. I’m like “I GET IT”. People have jobs, kids that need snacks every 5 minutes and houses that their snacking kids are constantly messing up. And their backs hurt and all they keep hearing is that they need to do their exercises if they want to feel better.
Well I’m here to tell you a dirty little secret: there is evidence out there that supports the fact that patients that don’t do their exercises can still get similar outcomes (in other words have equally less pain) if they pay very consistent attention to how they’re holding themselves and moving. You could call that permission for laziness but I call it efficient living. I prefer realism to idealism in most situations. So get out there and get those shoulders smack-dab over your hips (just as soon as you’re done picking granola fragments out of the couch cushions).
The Movement Mama 