Cage Theory — What is it?

Teresa S Landry
7 min readJan 13, 2022


Cage Theory isn’t about animals, and it’s completely G-rated. So, what is it? The cages I care about are inside each of us, and they are very much a part of our everyday health and well-being. The following is an excerpt from my book, Cage Theory: Healthy Joints for Active Lives.

A cage is generally thought of as a container with bars or strong mesh intended to keep something inside. Sometimes the something inside is there to keep what is outside safe (think: lions and people), and sometimes the cage is meant to keep what is inside safe (think: cat in a waiting room with dogs). Either way, the cage is meant to isolate what is inside and keep it there.

Each of the major joint areas in our bodies comes complete with a very well-designed cage. Surrounding each joint area where bones come together — I find it more effective to think of joints as areas rather than individual articulations — is a wonderful, interwoven mesh of muscles, cartilage, ligaments and tendons. This mesh surrounds the joint area to create a full cage that isolates and protects. This is good.

Some of the “bars” are small, and some are large, but they work together to keep the joint area safe and functioning. There are more than 650 muscles in the human body. Many of these muscles span more than one joint. The average gym workout doesn’t even come close to working 650 muscles. A good, full body weight workout is going to concentrate on about 30 major muscles. And those muscles do not get worked in all possible directions. That’s it…and that’s a good workout.

I have been through certification courses from multiple organizations, and they all concentrate on big muscles working in standard directions. Most of the people who have come to me for help with painful joints, balance problems, and injury recovery have had fairly good muscle development in standard directions. In fact, they usually didn’t understand why they were having problems at all.

Muscle strength and joint strength are not the same thing. Joint strength is dependent on the entire mesh being strong. As I already stated, the joint areas have very well-designed cages.

Unfortunately, well-designed and well-maintained are two different things. Cage Theory shifts the focus away from muscles and onto the joints.

When we are young and active, we automatically work the full cage in our daily lives (although video games are making this less normal). Sports, climbing trees, playing tag, climbing fences, crawling under tables, and trekking through the woods all tend to promote full development of joint cages. Anything that involves multi-directional travel, uneven surfaces, and navigating obstacles will work the entire cage of the joints being used.

Then, we get older. We work at desks and stare at computers. We sit for hours at a time. We watch TV lounging in chairs designed to annihilate our posture. When we work out, we do it in a very structured way that makes the prominent muscles look good, but does very little for the cages. We stop using the little muscles (and parts that are not muscles, but can still be strengthened) that we can’t see because, well, we can’t see them. It’s like cleaning behind the refrigerator — nobody sees the dirt, so how often do you really clean it? And when you start, do you wish you hadn’t bothered?

Suddenly — it always seems like “suddenly” even though the atrophy happened slowly over the course of years — we get hurt, or we fall, or we realize we can’t do the things that used to be easy. And it makes no sense to us.

The more sedentary our lives, the quicker it happens. For some who do the same exercises over and over to the exclusion of others, it can happen even faster than if they were sedentary. Why? Because the development is incredibly uneven, and the expectations are different. Stick with me on this one, because it really does make sense.

If you jog or bicycle every day, every day, all year long, and you think you are in good shape, you expect to be able to transfer that conditioning to other activities. Aerobically speaking, your body is primed and ready to go; muscularly speaking, not so much. I chose jogging and bicycling because they are demanding and rely on dominant muscles doing the same thing over and over without much deviation. It’s the lack of deviation that causes the imbalance. If your body is used to jogging in straight lines only and you decide to play tennis, you may be in for an unpleasant surprise. Your knees haven’t experienced a whole lot of side to side pressure, especially if you stick to groomed courses or treadmills. Instead of being primed for a different activity, you are primed for injury.

Someone who believes themselves to be “out of shape” may start playing tennis slowly and, therefore, safely. Someone who believes themselves to be “in shape” will push themselves harder using muscles that are underdeveloped in comparison to the ones they normally use, and create the conditions for injury. And because they are used to pushing themselves hard and are well-conditioned in one area, they will likely push themselves hard in the new area, so the injury could be severe when it happens.

So, Cage Theory is all about strengthening the cage surrounding the major joint areas. I work with areas instead of individual articulations because working individual articulations in single directions is part of the problem. Muscles and bones do not work independently, so we should honor that knowledge when we try to strengthen. The goal is to have full articulation and control in all directions that are anatomically possible.

This is not the same thing as flexibility, although that is a natural side effect. This is really about controlling the motion in all directions so that over-extension, dislocation, and strain are less likely to occur.

The main muscles associated with a given joint are really just the top layer. I like to call them the Spinach Muscles. (For anyone who grew up in the pre-computer age watching Saturday morning cartoons, the reference should be obvious.) The Spinach Muscles stand out and look impressive. They like to take over because they can.

If you have been around a young child, you may recall the child getting in your way while trying to be helpful. Patience only lasts so long, and it is fairly normal — at least it was for me — to get frustrated and eventually (hopefully, gently) shoo the child away so the task could actually be completed. When the little ones help, it seems that laundry takes twice as long, dinner gets messed up, and five extra spills have to be cleaned up instead of the one original spill.

If you stick with it, though, the children eventually become a real help and take over some of the chores.

Using this analogy, what is happening with the joint cages? Let’s use the hip area as an example. When we were young and moved in many directions, the cage developed evenly. As we got older and we stopped exploring our physical world with the same zeal, the less-used parts of the cage started to atrophy and the more used parts of the cage got stronger. Because we usually function on flat surfaces and straight lines, the side to side cage bars of our knees suffered the greatest decline, with the backward bars only slightly behind. The quads needed for walking and running forward — definite Spinach Muscles — got stronger and more inclined to shoo away the others.

What does that mean? Well, try lifting one leg up to the side. For most of us, the natural inclination is to slightly turn out the leg in order to make the lift easier. That’s the quad telling the abductor to go away because it can do a better job. And it’s usually correct. The leg lifts higher and more easily when the quad does most of the work. The down side is that the abductor gets weaker and isn’t there when you need it. In order to make the cage stronger, it takes concentration and effort to isolate the weaker muscles. Most people don’t take the time to learn how to do this.

As an instructor, there is nothing more frustrating than standing in front of an exercise class and trying to isolate a weak muscle like the abductor. Everybody wants to outdo everybody else by getting their leg higher (using quads); or they want to do what’s natural (using quads); or they are tired, so don’t even try to turn the leg in the direction I indicate (using quads, instead). If there is a mirror in front of the room, it’s even worse because the automatic thought is “higher is better,” so they use their quads because that’s the way the joint is built. This leaves the poor little abductor dejected, and it shrivels up even more…maybe not immediately, but do it for years and that’s what happens.

Then, one day, you’re hiking with your kids and that abductor is just what you need to keep you from sliding down the muddy slope you just climbed, and it’s not strong enough to help. You fall, twist something that wasn’t meant to be twisted, scream in pain, your kids scream in fear, and some kind stranger calls 9–1–1.

Sadly, this sort of thing happens all the time to people who are active, but do not fully work the joint cages. Until something bad happens, there is no reason to believe they are exercising wrong. Even after recovery (which is usually only partial because my observation is that the more “in shape” people are, the less likely they are to follow physical therapy directions and think they can do better on their own), people tend to see the accident as an unavoidable fluke.

I think that is why I have gravitated toward working with older adults and people who have chronic pain and repeated injuries. Until a certain threshold of inconvenience and agony is reached, the tendency is to keep doing what has worked in the past. The problem is that it really wasn’t working. When the 900 pound gorilla in the room can no longer be ignored, people are willing to back up, slow down, and relearn basics.

Cage Theory is about the basics of safe movement. Each joint area is capable of moving and/or resisting stress in multiple directions. Resisting stress in multiple directions is key to avoiding injury. That’s what Cage Theory is all about.



Teresa S Landry

Author, fitness trainer, filmmaker, homesteader, figure skater, and Jill-of-all-trades-as-needed (in other words: entrepreneur).