Practical Science on Movement and Pain
Practical Science on Movement and Pain
What are your physical limits? What is your body capable of? How fast, how far, how strong, how long? In all likelihood you will never know, because your brain will probably never let your body reach its real limit. And that’s a good thing, because that will help prevent you from breaking bones, straining muscles, dislocating joints and maybe even killing yourself.
Put another way, many of your physical limits are imposed by your brain, not your body. And I don’t mean that in the sense that is conveyed in various inspirational commercials by multinational shoe companies. I’m talking about the fact that the brain is a governor.
A governor is essentially a feedback device on a machine or engine that is used to provide automatic control of speed, pressure, or temperature. Part of the reason engineers build governors into machines is to prevent them from causing damage by getting too hot, going too fast or basically just getting out of control.
The body is also a potentially dangerous machine. Muscular effort can easily cause physical damage when it happens too fast, with too much force, and goes on for too long. So the central nervous system is equipped with numerous systems that provide automatic and unconscious control of potentially dangerous movements. In effect, the nervous system acts as a governor.
In this post and the next few posts, I will talk about how the limits of our strength, flexibility and endurance are determined by the brain based on feedback from the body. I’ll also discuss how these limits respond to changes in circumstance. In this post, I’ll address governors in relation to strength.
The forces created by muscular contractions are useful for moving us around and helping us get a bigger bench press, but as noted above, they are also potentially dangerous. We can get a good idea of how destructive muscular force can be by considering the effects of severe electric shock, which causes involuntary and extreme muscular contractions. These are so powerful that they can dislocate joints, break bones, throw the body across the room, and cause brain injury through huge rises in blood pressure.
Dude, that is some awesome strength! How did you get so buff bro? Actually, all of us are that buff, but our nervous systems are designed to prevent bone breaking displays of force. Bummer. As Eric Cobb says, the central nervous system is built for survival not performance, and if it has a choice between keeping you safe from injury and allowing you to max out your bench, it will pick safety every time.
But the good news is that it appears we all have some at least some untapped strength potential, if we can only get the brain to ease up a little on the governor that limits it. Vladimir Zatsiorsky, a professor of kinesiology who is an expert in resistance training, estimates that the average person can voluntarily utilize only about 65% of their potential muscle power. (A trained powerlifter might reach 80%). As kettlebell guru Pavel Tsatsouline says, your muscles are already capable of lifting a car, they just don’t know it yet.
So how do we get the governor to cut us some slack? If we consider that its basic purpose is protection, it would make sense that any feedback to the brain indicating that a particular movement is safe will tend to increase the brain’s willingness to allow sufficient force to produce it. Following is a discussion of several ways in which strength is affected by factors bearing on the relative safety of the movement in question.
If the brain limits strength to protect us, then pain should make us weak. There are at least two studies that address this idea directly. In one study, researchers found people with painful knees, made them stop hurting by injecting a local anesthetic into the knee, and then measured the effect on knee extensor strength. In the second study, they did the opposite. They took people with pain-free knees and made them hurt by injecting a solution into the knee, and then assessed the effects on strength. Guess what, the subjects in the first study got stronger, and the subjects in the second study got weaker. Not too surprising, but it is easy to forget that reducing pain is one of the fastest and easiest ways to increase strength. How many times have you decided to train strength at a sore joint instead of resting it?
A joint that is uncoordinated is more likely to get hurt than a joint with better movement skills. I have previously discussed the idea that coordination depends on a clear movement map, and that the brain is likely threatened by a joint that is uncoordinated or lacks a clear map. Does map clarity affect strength?
There are several studies that suggest it does. In one representative study, researchers found that hip strength increased after hip mobilizations designed to explore end ranges of motion and create novel mechanoreception. My interpretation is that the mechanoreception created additional (temporary) map clarity, which reduced threat, which lowered the governor on strength.
We would expect that the brain would consider familiar movements to be safer than novel movements. There are two reason for this. First, if you don’t have any experience with a particular movement, you need to exercise special caution because you don’t know the potential dangers. Second, lack of experience means lack of the specific skills needed to execute the move with optimum safety. So we should expect that people are much stronger at activities that are familiar and weaker at activities that are outside of their normal experience.
This is exactly what happens when you start training a new exercise. Regardless of your previous training to develop the muscles and ranges of motion used in the new exercise, you will be relatively weak in that exercise until you practice it a little. As you gain familiarity, you will gain strength rapidly. And this strength will not necessarily be transferable to contexts that are unfamiliar. Studies have demonstrated that strength gains from a six-week training program can only be measured with tests of strength that are familiar, and cannot be measured with tests that are unfamiliar.
Of course it is well known that most of the initial increases in strength as a result of resistance training are due to neural adaptation – increases in the amount of muscle fibers activated at one time, changes in the rate and order at which they fire, and reductions in the amount of inhibition to such firing. I think we can look at all these neural mechanisms as part of the machinery of the governor – the collection of processes by which the nervous system makes sure that you only have full strength in motions that are known to be relatively safe.
So it appears that the brain will limit strength because of its preference for safety over performance. But what about an emergency situation where safety requires performance? Does strength increase in an emergency situation?
We have all heard the common tale of a mother who lifts a large car off her trapped baby. This has all the hallmarks of an urban myth and I couldn’t find any evidence that such feats have been documented. (If you find some please let me know in the comments section below.) But it does appear that emergency situations can increase strength, if not to superhuman levels. For example, strength increases after hearing a gun shot. Perhaps the mechanism is an adrenaline rush. Or something else. Whatever the mechanism, it is consistent with the idea that the brain doles out strength as it sees necessary, depending on the circumstance.
If you wanted to convince your dad to give you the keys to the Ferrari (and not the Ford Fiesta), what would you do to convince him? You would prove to him that you have good driving skills, that you know how to drive a Ferrari, that the Ferrari doesn’t have any mechanical problems, and that you know the road and where you are going. And if that doesn’t work you could fire a gun off nearby and pretend there is an emergency.
If you want to convince your brain to make you strong, use some similar persuasion. Show your brain that you know what you are doing and won’t get hurt doing it. Get out of pain, even mild pain. Coordinate your joints with mobility drills. And don’t forget to lift some heavy weights somewhere along the line too.
What do you think? Let me know in the comments below.
In the next post I’ll discuss central governors as they relate to flexibility.