It's easy to think of muscle control as a brute force technique for controlling the body.
However, muscle control is actually a requirement for proprioception.
If we didn't have muscles we wouldn't be able to feel our body. We wouldn't have "proprioception".
If we didn't have muscles, we wouldn't be able to move, either, which is kind of the point of having joints and muscles.
Not only that, but we need muscle control to protect our joints. It is what can keep them lubricated, preventing wear and tear on our joints articulating surfaces and protecting our joint capsules.
It might seem ironic or strange, but you can learn a lot about lubrication by reading about marine engines, particularly in regards to propellor shaft lubrication.
Obviously a concern is preventing wear and tear of the prop shaft as well as the bearings, the things that support the prop shaft.
Marine engines can be particularly difficult to work on due to confined spaces and dealing with water seals etc (the type of seals that prevent the ingress of water, not the type of seals that live in the water).
But with regards to prop shafts, the type of lubrication is important since one type of lubrication in particular results in more wear and tear.
Also important is understand the conditions that different types of lubrication occur under.
Without muscle control it's very easy for our supporting joints to rely on boundary lubrication.
This is a type of lubrication that involves contact between surfaces.
Basically, your joint surfaces rub against each other. This causes these surfaces to wear away over time. And sure, our joints are designed to repair themselves. To an extent. However, why rely on this method of lubrication when there are other options!
In the case of marine engines, boundary lubrication tends to occur at low speeds. You'll understand why this is important after reading about hydrodynamic lubrication.
As for the human body, this could be deemed the fail-safe lubrication method. It is how joints are lubricated when either of the next two lubricating methods are not engaged.
The problem with this lubrication mode is that it results in wear and tear over time.
And sure our bodies can repair themselves, but why put the body through unnecessary wear and tear (and risk the need for a joint replacement operation) when there are other options!
With muscle control applying tension to joint capsules, hydrostatic lubrication becomes possible.
In this case, tension in the joint capsule pressurizes synovial fluid, preventing it from being squeezed out from between joint surfaces.
This means that joint surfaces last longer because they aren't being worn away.
This can be especially important for static yoga poses where the joint in question is bearing weight.
How is tension added to the joint capsule? By muscle activation.
In some cases muscles attach to joint capsules directly via tendons and ligaments. Thus when those muscle activate, joint capsule envelope tension is increased via those tendons and ligaments.
Muscles can also affect joint capsules indirectly via bursae.
The main example of this is at the knee joints where there are bursae situated between tendons and ligaments. In these cases, tension in tendons is transmitted to ligaments via the intervening bursae (which are sacs filled with synovial fluid).
Those ligaments, assuming a connection, can then cause changes in tension to the joint capsule envelope.
In marine engines, hydrostatic lubrication is created by pressurizing lubricating fluid by a pump.
And so you could think of the joint capsule envelope as acting like a hydraulic pump with muscles providing the necessary power for that pump.
This type of lubrication can be achieved via an effect which is very much like (or the same as) the hydroplaning effect.
Hydroplaning tends to occur at or above a particular speed, assuming that there is enough liquid on the road surface.
With hydrodynamic lubrication, the high speed of one moving part relative to another creates a "wedge" of lubricating fluid that helps to keep mating surfaces from contacting and rubbing against each other.
So if mating joint surfaces are moving quick enough relative to each other, a layer of lubricating fluid is drawn in between the mating surfaces by the high speed of one relative to the other.
Examples of how this could happen in the body is swinging the lower leg relative to the upper leg at the knee joint or swinging the thigh relative to the hip and the hip joint. If relative velocity is high enough between mating surfaces, lubricating fluid is pulled into the gap between mating surfaces helping them to slide relative to each other without actually contacting each other, like car wheels hydroplaning on a thin layer of water.
In marine engines, this type of lubrication occurs above certain prop rotation speeds.
As with hydrostatic lubrication, hydrodynamic lubrication also results in less wear and tear on the joint surfaces.
Relative velocity just means the speed of one moving part relative to another.
Generally when we talk about speed, or how fast we are going, it's relative to the earth.
With joints, relative velocity means the speed of one joint surface relative to another.
From the proprioception angle, muscle activation is one "quality" that we can feel.
Muscle activation at the back of the thigh and hip in a standing forward bend can give us a feel for our thigh and hip bone. It creates a pull on the ischial tuberosity and the PSIC helping us to feel those points of the hip bone.
If inner and outer hamstrings are active, it will create tension at the back of the knee along both the inner and outer aspects, helping us to become more aware of our knee. And if the deep fibers of the gluteus maximus are active we'll get a sense of the back of the upper part of the femur. If the biceps femoris short head is active then it will give us a sense of the remaining length of the back of the femur.
Muscle activation isn't an isolated event. It creates tension in connective tissue and that is something else that can give us a feel for our body.
In a standing or seated forward bend with the hamstrings relaxed, there will be a lengthening sensation at the back of the legs. If, while in a forward bend, you turn the hamstrings and/or glutes back on, the sensation can become slightly different.
Contracting a muscle while it is lengthened "dampens" the muscle activation signal. And if a muscle is in stretch then this signal can become intertwined with the stretch signal. Both sensations can give you a sense of your body (and what is happening to it).
Exert hip flexors and hip extensors against each other, (and include other muscles of the hip joint as required) and you can get a sense of your hip joint. Do the same thing in a forward bend or back bending hip position and you can feel you hip joint in those two configurations.
Likewise with the knee joint. Activate quadriceps, hamstrings, the long hip muscles, and the gastrocnemius and you can get a fairly solid feel for your knee whether it is bent or straight.
And that's something else about muscle control.
Some people think that just because a knee is straight the muscles of the knee joint are relaxed. Or if the hip joint isn't flexed then the hip flexors are relaxed.
Because of this, muscles can help you proprioceive your body no matter what you are doing. The only proviso is that you need some sort of muscular activation.
Muscle control principles includes an overview of muscle control and some important principles that can help you better understand how you can feel and use your body.
To actually begin learning muscle control, check out the products page. All of the videos and ebooks are written or produced by me and are designed to help you better control, feel and understand your body.