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How Injuries Happen

To understand injuries and how to deal with them, it’s helpful to understand how they happen. In the biz, we call it ‘mechanism of injury’, or ‘MOI’ for short. This article discusses what I believe to be the primary MOI’s for the majority of musculoskeletal injuries. Oversimplified, of course.

A recurring cause is excessive force. So, remember basic physics:

Force = Mass X Acceleration (too much, and too quick!)

Excessive force in a direction that you shouldn’t be able to move. This usually results in a sprain (click here for a review of sprains vs. strains). Quite simply, your joints aren’t meant to be able to move in every direction imaginable. Look at your elbow for example: one of the most boring joints in the body. Your elbow can flex, and it can extend. That’s it. (Supination and pronation happen at the radio-ulnar joint, smarty pants).

Totally stole this image from another site.

You can’t make your forearm bend sideways at the elbow joint (abduct or adduct) like your hip or shoulder joint could. If you force it to, you get injured.

Stole this one too!

These injuries cause sprains. This is because ligaments and various other connective tissues limit this movement from happening. As shown below (pictures are so helpful!).

Some examples include rolled ankles, shoulder separation (AC joint sprain), and sprain wrists. All of which suck really bad and hurt a lot. They also take a while to heal, depending on how bad it is.

Important point: think about it… how can you possibly avoid this injury by being flexible? You can’t. The only thing you can do to avoid this type of injury is be aware of your body, and careful in your technique.

Now on to the next MOI:

Excessive force to a resisting muscle. This usually results in a strain. You get these injuries when you apply way too much force to a contracting muscle. Muscles that are not strong enough to resist this force end up being torn (either microscopically OR a full out tear that you can literally see).

Most muscle injuries happen during ‘eccentric’ contraction (muscle is working, but stretching too, like lowering a weight) and within the normal range of motion (not the end, which will be discussed next) 1,2.

Oh Snap! Literally.

If the muscle isn’t resisting, you would just drop the weight. No strain. Hopefully it don’t land on your foot.

Usually you reflexively drop weights that are too heavy, but if you voluntarily resist the load, trouble can ensue. You either have to be strong enough for the load on your muscle, or… rip! Classic strain.

Another common example: quick direction switches during sports.

Remember, it’s too much force that’s the problem.

Overstretching a muscle. Strain, and possible sprain (keep reading). This MOI is actually very similar to the above, but instead of applying force to the muscle as it resists, you apply force by stretching past its available range. Either way, it’s still excessive force that causes the damage. A muscle strain ensues.

Yours truly.

What’s different about this is that when you bring your muscle to the end of its length, it tightens up, whether the muscle is active or not. It’s like stretching a rubber band: resistance increases as you pull.

This is the injury that people try to avoid by stretching. The logic sounds good at first: get more flexible = muscle longer = less chance to overstretch.

But the reality is: not so simple. First of all, when you increase your flexibility, how much of an increase in your range of motion do you get? Usually just a few degrees of rotation around a joint. When you overstretch, it’s usually an accident, so really you just delay the inevitable by a millisecond!

Furthermore, you can’t just make yourself infinitely flexible. If your muscles are so loose that you can’t overstretch them, eventually you are going to start putting force on connective tissue as you keep going further. Then, you get a sprain, like the first MOI above. Sorry, but being flexible does not help that much. Flexible people still get lots of injuries.

Impact. Resulting in ‘soft tissue injury’. Excessive force. Period. Not much to explain here. No picture necessary.

This happens when you fall on your butt, and you get a bad bruise. But really bad falls can cause broken bones, concussions (if you hit your head), or worse. At the least, a fall can cause soft tissue injury.

Soft tissue injury can appear like both a sprain and a strain. If you damage muscle, it hurts to contract it. If you hurt a ligament, it hurts to move that joint.

Sometimes its not what you do, its how much!

Overuse injury (also known as repetitive strain injury, or RSI). Repetitive overuse can result in a lot of confusing and strange injury-like conditions, that can be best described as ‘degeneration’. They are not always inflamed 3, despite popular belief 4.

They almost always hurt. Pain is a common symptom, and don’t always make sense. Sometimes, it’s very hard to distinguish whether something is actually an RSI or actually a chronic pain problem (changes in your nervous system, not damage).

It’s hard to say what causes the classic overuse conditions: tendinitis, tendinosis, carpal tunnel syndrome, etc. etc. There is even evidence that poor nutrition 5 and abnormal inflammatory processes 6 are important factors in developing osteoarthritis: the classic ‘wear and tear’ condition were all supposedly doomed to suffer from when we get older.

But one thing is generally agreed upon: we need rest. You can’t just keep tearing your body down with activity without giving it a chance to recover.

Furthermore, you can’t just keep wearing things down without trying to build them back up: which is why I strongly believe in strength training (not to be confused with body building) as the complimentary training of choice for the majority of all activities.

In Summary:

Injuries can happen in a variety of ways, unfortunately.

  • Most of them involve excessive force, in the form of either 1. an abnormal direction, 2. a normal direction, but too much force, or 3. a normal direction, but too far, or 4. direct impact, like a fall. All of these are usually innocent mistakes.
  • 5. Overuse injuries occur due to too much wearing down (repetitive activity), and not enough building back up (rest, exercise, and nutrition). (see Exercise vs. Activity)
  • The only mechanism of injury that stretching might help with, is number 3, and even that don’t seem very likely.

Now, it might look like I hate stretching. But I don’t. Stretching improves range of motion, which can be very important depending on what your goals are. If you dance, it’s hard to kick high without flexibility. I just want to make the point that stretching don’t do a whole lot to prevent most injuries.

What can you do to prevent injuries? Some sensible ideas, coming soon!

For now… just don’t be stupid!!!



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    3 Responses to How Injuries Happen

    1. Tony Ingram says:

      FYI: I’m grossly oversimplifying the use of the terminology: MOI. When it comes down to diagnoses doctors make, and whether to cast you, or even do surgery, MOIs are very specific. As a radiology resident friend of mine pointed out, the radiograph at the beginning is a ‘maisonneuvre fracture’ MOI: external rotation.
      Again, another reason you should run to the Doc first after a bad injury!

    2. “Again, another reason you should run to the Doc first after a bad injury!”
      Unless of course you have sprained your ACL, or strained your Biceps Femoris. Then you should limp?

      Sorry, smart ass – couldn’t help it. Great article Tony!!!

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