Understanding the Forces of Sport Injury

Imagine a cardboard box. It’s a fairly stable structure that can withstand a certain amount of weight placed on it.  For example, if you placed a one-pound weight on that box it would likely be able to hold that amount of compression.  Now imagine adding another one-pound weight and continue to add weights one by one. At some point, if you keep adding one-pound plates on that cardboard box it will collapse. This seems to be a simple concept that I’m sure everyone can understand.  So why do people have a hard time accepting this when it comes to our anatomy and biomechanics?

Everything Can Break

Before we get to that, let’s lay the groundwork for the discussion. Every tissue in our body has a breaking point. Everything can break.  I’m sure every material in the world has a breaking point but for the scope of this blog we’ll keep it to anatomical tissue.  Muscle, bone, tendon, ligaments, nerves…they all have the potential to be damaged. What differs between these tissues is the force required to cause damage. For this blog, we’ll stick to using bone as an analogy since it’s probably the easiest for everyone to understand.

Bone can be damaged with both compressive and tensile forces. The easiest to understand is that of compressive load which causes bone injury. How the force is applied is an important variable. A repeated load can lead to a stress fracture. This is common with elite runners who ramp up their training to a point that the bone can’t keep up with the constant pounding. What results is a series of micro-fractures that can eventually coalesce into a very severe bone fracture. Bone can also be injured through a one-time load.  This type of bone fracture is the one we can all understand easily, the most common type. An example is a broken arm or broken leg after falling or being tackled during a sport.  In these cases, the bone tissue tolerance is not great enough to withstand the force applied. Rate of load and the total area that the load is applied to are also important variables related to tissue injury and the tipping point of injury. As you can guess, this is not an exhaustive list. The important point here is that all tissues have a “tipping point” of injury. When a force is greater than what the tissue can withstand, injuries occur.

So, let’s apply this concept to the example of a squat. Imagine you’re at the gym and you have a bar on your back, ready to do a squat. You put twenty pounds on each side and do a set of squats. Your vertebrae were subjected to compressive forces during the exercise, but you’re not in any pain. Your legs feel totally fine, so you’re ready to add more weight. In fact, your form is perfect (since technique is really important at your facility) so the limiting variable for adding weight is the strength in your legs. As long as your technique is perfect, injury cannot occur. Not true!

Even Perfect Exercise Technique Cannot Guarantee Your Invincibility

There is no published study in any credible journal that will tell you that perfect exercise technique will guarantee that you won’t get hurt. This simply isn’t true. The vertebrae (for example) have a “tipping point” as mentioned above. Even if your legs can handle more weight to squat, your boney vertebrae may not, regardless of how perfect your form is. Think back to the cardboard box analogy.  At some point, if you keep stacking weight on that box it will collapse. The same can happen with our bone, regardless of exercise technique. How much load can the bone withstand? It’s difficult to say since it’s different for everyone.  Some patients might have osteoporosis which will lower the ability of the bone to withstand compressive forces.  Another situation is the concept of bone remodelling after continuous training.  In theory, if you trained really hard for a month and caused some micro-fractures in the vertebrae (which you cannot feel) you could be more susceptible to injury with a heavy load. If you decided to set a personal best resulting in a high compressive load on a damaged area a compression fracture may be the result.

The intended message for this blog is that every tissue has a tipping point of injury. It’s a basic concept but perhaps often forgotten. Perfect technique in the gym helps to limit the chance of injury but it does not make you invincible.  Be wise with your exercise program and choose exercises and loads that are suitable for your physical health. Don’t fall into the false sense of security that injuries cannot occur if your technique is perfect…they can!

 

Written by Dr. Kevin McIntyre – Clinic Director, Burlington Sports Therapy

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