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How Does A Muscle Fail?

Muscle Failure

In the previous post “Why Do Muscles Cause Pain?”, we looked at the muscle alert system which sends graded messages to the brain. It alerts the brain when blood flow has stopped and gradually increases the intensity of the message as time passes.

An initial mild awareness turns to discomfort and then severe pain, waking us up if need be, unrelentingly telling us to change position or relax the muscle to allow blood flow to return. This highly evolved blood flow alert system is vitally necessary to keep our muscles alive, as they can quickly become damaged if their blood supply is cut off for too long.

This system is designed for the two main causes of blood flow interruption that we experience during every-day life; contraction and compression. When either of these two activities has gone on too long, pain sets in and we have to respond, either by relaxing those muscles or changing position. The change is instantly rewarded with an easing of the pain. We respond to this pain many times during our day, thinking nothing of it.

What if one day that pain did not ease? Instead it increased and spread, continually demanding attention and not responding to anything you did for it. As investigations and treatments fail to help, often making things worse, your ability to work slips, your friends stop calling and you begin to wonder if anyone believes you.

Welcome to the hell of chronic pain.

I’m going to outline the key to understanding this all to common scenario that needlessly affects up to 25% of the global population. For 95% of all people currently suffering with chronic pain, this message is for you.

Muscles are designed to cause pain when their blood supply is interrupted. When we accept that muscles quite readily fail in their daily tasks of contracting and relaxing, getting stuck in the latched or closed position which cuts off their blood supply, we then can see that the solution lies in fixing the broken muscle. Attempting to suppress the pain or live with it is a futile effort.

The importance of understanding the mechanism of muscle contraction and relaxation is that with this knowledge we can create the right environment within our muscle cells. When they have what they need they can function normally, able to relax when needed and maintain a healthy blood flow.

Muscle Contraction And Relaxation

Muscle tissue is designed to shorten or tighten when required, at variable intensity and in co-ordination with other muscles, to provide complex movements and body positions. Each muscle cell has millions of protein rods that overlap each other. The overlap is variable with the rods being able to slide across each other, pulled along by powerful ratchets that slide the rods into contracted or relaxed positions. When this is multiplied in all of our cells and coordinated, we get the power and beauty of movement.

Muscle contraction is controlled by dedicated nerves that travel from the motor cortex in the frontal lobe of the brain down the spinal cord and out to each muscle spindle or segment. These nerves are called motor nerves. There activity is modulated along the way to the muscle. The cerebellum at the back of the brain influences the coordination of movement to provide “muscle memory” and allow repeated complex movements such as walking without us having to think about it.

The default position for a muscle cell is to be relaxed, with the protein rods kept comfortably apart and the ratchets unlocked. This occurs at rest, when we tell them to. The cell is relaxed but ready for action.

If the motor nerve is severed or the connection to the muscle is interrupted the muscle is then deemed to be paralyzed and cannot contract.

The call to action comes when the motor nerve sends a signal to the end of the nerve (nerve terminal) causing a chemical messenger (acetyl choline) to be released into the narrow junction between the nerve and the muscle membrane. This messenger in turn opens channels on the muscle membrane that allows potassium to leave the cell and sodium to replace it – a pretty standard nerve switching mechanism in the animal world. 

The “contract” signal is then carried directly to a special container (sarcoplasmic reticulum) within the muscle cell that contains calcium – lots of it. The calcium is released in a rush, flooding the cell, overpowering magnesium and causing a powerful response – causing the ratchets to slide the protein rods across each other – contracting the muscle cell. The calcium release that overpowers magnesium and causes muscle contraction is known as the second messenger system.

The more cells that are commanded to contract, the stronger the overall muscle contraction will be. If a maximal contraction is not needed, the motor nervous system intricately sends messages to different cells within the muscle, remembering who needs a break and spelling them off!

When the motor nerve stops demanding action (contraction), the muscle goes into relaxation mode. Relaxing requires the cell to pump the calcium back into the storage bin. Returning calcium requires a lot of energy as the calcium is much happier chemically being spread around the cell. Once the calcium is cleared and magnesium takes over control of the ratchets, the rods slide back into their comfortable position.

I must confess that this is a very simplified account of what happens. Just as starting a car and driving off down the road can be considered a simple task and series of events, full disclosure of the full sequence of events could fill a book. There are entire books written about how muscles work, but our for our purposes a general understanding is more than sufficient. 

You can read a more in-depth account of how muscles work here.

When It All Goes Wrong!

As with most things in life – things can go wrong. Muscles, like all other organs, can and do fail. If they are ordered to do more than they are used to or capable of at that point in time (excessive contraction with relatively poor blood flow and energy reserves) – they will fail. Sometimes it can be a single violent movement (such as whiplash injuries), repeated movements  (prolonged coughing or shoveling snow), or staying in a bad posture for too long (sitting hunched at a desk). Everyone has a memory of a time when their muscles failed and they suddenly developed severe pain. 

The part of the muscle contraction-relaxation sequence that takes the most energy and is prone to failure is the relaxation phase. Pumping all that calcium back into storage takes a lot of energy (which is produced by mitochondria) to run the calcium pumps. When they fail, muscles ‘lock-up’. The painful experience of a locked muscle is caused by un-cleared calcium.

Energy failure allows the calcium to stay at large in the cell, overpowering magnesium and keeping the cell contracted, even when the motor nerve has stopped demanding action. This is called a ‘latched state’. At this point things start to go horribly wrong! Soon, nothing outside of the cell is going to have an impact on changing this state.

The only way to solve this problem is to turn the calcium pumps back on, so that calcium is returned safely to where it is stored in the sarcoplasmic reticulum. When the muscle is relaxed and blood supply is restored, the cells will gradually re-energize and restore health. The sooner this is done the better.

The Calcium/Magnesium Switch

Our muscles are constantly releasing calcium to create contraction and putting it back in storage to return to a relaxed state. Without this function we would not be able to move, and if the switching is imbalanced by the body being overwhelmed with either magnesium or calcium there can be serious repercussions.

Early in my medical career, I witnessed first hand how powerful magnesium can be as a muscle relaxant. I was a first-year anesthesia resident at the time and had been called for a “code blue”, a situation in which a patient requires resuscitation or immediate medical attention. The patient was a 50-something, healthy looking man in the coronary care unit, recovering from an uncomplicated heart attack. When I arrived he wasn’t moving. He was completely paralyzed.

My fellow resident doing her cardiac rotation that month had already figured out that a magnesium dosing error had occurred, with ten times the intended amount being given intravenously over a short period of time. Paralysis is the anesthetic state of choice – we do it all the time, paralyzing patients under anesthesia to facilitate both the surgery and ventilating (breathing for) the patient.

I intubated him (inserted a breathing tube) gently and started ventilation, nothing unusual here. Problem is, magnesium works on all muscles, unlike our paralyzing drugs that only work on skeletal muscle. The patient’s heart wasn’t contracting strongly enough. Even though the cardiologist and nephrologist gave him as much calcium as they thought appropriate to restore balance, it was too late, we could not reverse the heart muscle weakness and he slipped away.

That has stuck with me forever, as I witnessed how powerful magnesium can be in relaxing muscle, to the point where the heart cannot even function. Now, had that been a calcium overdose, his heart would have turned to stone, unable to relax and filled up with blood between contractions. 

Sustained muscle contraction can be witnessed after death, when all blood flow ceases, muscles run out of energy and the calcium pumps fail. The calcium breaks out of storage and floods the cells, just as if it had received the signal to contract. The muscle latches and becomes rigid (rigor) – something we know of as rigor mortis (rigidity of death).

A muscle taken to the point of exhaustion is flirting with the rigor state and needs care after such activity. A poorly maintained muscle will always be close to exhaustion regardless how little is demanded of it.

The on-off switch in muscle is magnesium and calcium. Maintaining the balance between calcium and magnesium is crucial for proper muscle function. If muscles get overwhelmed with either, problems follow.

Over the next few weeks we will take a more in-depth look at muscle failure in chronic pain, trigger points, and how we can restore calcium/magnesium balance.

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