January 11, 2019

You hear or read about overloading joints.  It leads to lameness.  Some people will tell you to protect the joint, you should inject some stuff into the joint fluid. But what is it really to overload a joint?  If you overload your truck with too much hay it you can see that it is overloaded. It squats in the back, the front end is higher and lighter and maybe it has sketchy steering. If you keep doing that, something is going to break sooner than it would if you didn’t do that. The common way of overloading a joint of a biological system, the way we either cause lameness from riding, or fail to prevent it, is different in most cases. (This is not to say you can’t put too much weight on a horse!)

I saw yet another worn out hair elastic on my dresser. They don’t last very long; it’s maybe 150 installations or so before the elastic has pulled out of the clamp. I thought; this could be a good way to illustrate joint overloading.

The hair elastics fail as a result of overloading but it has nothing to do with weight. The loading on the hair elastic is tension loading. The overloading is from repetitively stretching it, a little too much, to go around a ponytail. I say “a little too much” because it doesn’t fail the first time I over stretch it or the 2nd or 3rd or 132nd before it starts to pull away from the clamp inside the cloth cover. I can stretch it using weight, but, regardless, the force IT experiences is tension. The loading on joints is also tension loading but take your eyes off the bones and joint capsule for a second. Under normal circumstances, joints are not getting compressed together. The muscles and soft tissues, through tension, are maintaining the joint space in the most balanced manner possible through tension.

So what is balance? I can stand balanced in a really awkward position, twisted, hunched over, head turned, while standing on one foot. (I demonstrate this sometimes, so if you don’t want to do it, just picture me acting a fool.) Basically if I don’t fall down, I’m balanced, right?  But, that takes muscular effort greater than what is needed for neutral balance which is what I have when standing in perfect posture. In the awkward position, I will fatigue more quickly than I would standing straight. Try it. It’s a time consuming experiment. Neutral balance is the most efficient. In terms of bio-tensegrity, tension of soft tissue is creating structural integrity both statically (standing still) and dynamically (during locomotion). “Essentially, tension is always trying to reduce itself to a minimum and form a straight line, which is one of the most important factors in the self-balancing ability of tensegrities.” (Graham Scarr “Biotensegrity, The Structural Basis of Life”.)

Let’s apply it to walking because no living horse or rider is static, we just use statics to introduce concepts that grow exponentially in complexity with motion, especially when you try to describe them with math. You can walk twisted and bent over and limping without falling down. That’s balance because you didn’t fall down.  But it’s not neutral balance, it’s quite lame, and you will tire more quickly because it’s not efficient – because it requires extra muscular work.  If you moved that way for an extended time, you would start to develop arthritis somewhere, muscles that would be used in neutral balance will weaken, the muscles maintaining the wonky balance may strengthen and you will eventually get used to walking that way.

The overloading of soft tissue at the attachments to bones leads to cellular signaling that results in the growth of extra bone material in an attempt to strengthen the connection. That’s the arthritis or DJD lesion you see in xrays. Exactly where pathology will form depends on the kinematics, muscular development, and muscle combinations the body chooses as the solution to maintaining balance. This is different from a huge trauma that tears soft tissue or breaks a bone. It’s repetitive stress of the bad variety. (see Mechanics for Equestrians II). There is also repetitive stress of a good variety that will strengthen structures – it involves working the horse at his or her natural cadence.

Imbalance in motion will cause imbalanced muscle action which will overload joints – remember, not like an external weight.  The overloading that creates much of the lameness related to riding, in any discipline, is too much repetitive imbalanced tension. Overloading. The opposite of overloading is efficiency. That’s it in a nutshell.  With education in biomechanics, it is possible to see and feel overloading before a gradable lameness is detected through lameness examination, even with a lameness detection device. That is the best time to fix it. Even if you don’t have the language to describe it, you feel it. Don’t let anyone tell you there is nothing wrong.  All that means is they don’t know how to help, but there is help.