Understanding and Controlling Injury: The Law of Repetitive Motion

Photo Credit:  Ben Solomon/The New York Times/Redux/REA

Unfortunately, injury is a part of life and a part of sports.  If you play long enough and push hard enough (which you’ll have to if you want to be good) you’re bound to run into little tweaks and pulls every now and then.

The key is to minimize there frequency, ensure quick recovery, and avoid the big guns like your ACL.

Step numero uno in avoiding injury is to understand it.

Why does it happen?  What factors make me more likely to become injured?  And stuff like that.

Unfortunately, most people don’t have the slightest understanding of injury and shrug it off as an unfortunate circumstance.

Don’t be one of those people.

With the right approach you can both understand and prevent it (well…prevent may not be the best word, but you’ll be better at limiting it than your peers).



Let me introduce you to the law of repetitive motion–aka the most user friendly injury equation of all time.

As you can see, 4 variables dictate your likelihood of getting injured:

I (injury)

Don’t feel like this one needs explanation.

N (number of repetitions)

The obvious explanation is the number of reps you perform of a particular exercise.  For example, doing 5 reps of the back squat versus doing 72.  Here are a few other items it applies to as well:

Steps taken throughout the day

Bending over to pick something up

Reaching up to grab something out of the cupboards

Throwing a baseball

Sitting (yes…that’s right…sitting counts as one gigantic rep)

Does this mean the answer is to try and keep N as low as possible?  No because you also have to consider form.  An individual who moves well and has good form can afford a higher N than an individual who moves poorly.

F (force)

This is kinda confusing, but it’s the force of every repetition as a function of maximal muscular strength.  Thus, if you increase your maximal muscular strength F will decrease because your body is better able to handle the external load.  Here’s a really simple example (I understand that this is way oversimplified, but it’s just to help you see the point):

Maximal muscular strength subject a:  100 newtons

Maximal muscular strength subject b:  75 newtons

Force form external load:  60 newtons

Which subject is better prepared to handle the load?  Or which subject will the load have a greater impact on?  It’s subject b because he or she is weaker.  At the end of the day, being strong reduces the amount of force placed on the body.

A (amplitude)

Amplitude, in its simplest since, is range of motion.  The tighter you are the more prone you are to injury (sort of).  On the other end of the spectrum, you can be too loose.  As I mentioned before in Why You Should Squat and Deadlift Heavy, you have to think of range of motion on a continuum.  At one end of the spectrum is the bodybuilder who has a fair amount of stability but horrendous mobility, and on the other end is the yoga queen who has way too much mobility and zero stability.


Like the bell curve above illustrates, the best place to be is somewhere in the middle.  You want a good balance between mobility and stability.

R (relaxation)

I can’t stress the importance of quality relaxation enough.

Being able to unwind and hit the chill button has a large impact on your bodies ability to recover.  Unfortunately, relaxation doesn’t carry much weight today.  People are constantly jacked up on caffeine running from their apartment to work, from work to the gym, from the gym back to work, from work to home to do more work etc. etc.

This type of lifestyle tends to jack up your sympathetic nervous system (the one controlling your fight or flight response), and keeps it turned on all the time.

That’s not supposed to happen.

From a biological standpoint, the sympathetic nervous system is supposed to be turned on rarely (key the name fight or flight).   It’s supposed to be what kicks in when you’re foraging in the woods for some berries, and a giant black bear pops up trying to eat your face.

I know the deadline your stressing about, or the traffic you hit in the morning doesn’t seem as bad as the bear, but your body doesn’t know that.  It’s not going to differentiate between the two.  It views stress as stress.

Anywho, the ability to flip the switch and get back into the parasympathetic nervous system is vital to your overall health, and it’s something I recommend you practice.


With all of that mind, here are some key takeaways to help you limit injury:

Keep N small by not staying in one posture for extended periods of time (sitting at work), or repeating the same thing over and over again (cough cough people who have their kids pitch year round for multiple travel teams)

Keep F low by getting strong

For A, if you’re hypermobile spend time stabilizing your joints.  Stretching for you will only create greater instability.  If you’re really tight and missing range, then you need to figure out why.  Is it an alignment issue?  Is it a capsular issue?  Is it bony restrictions?  Is the muscle short?  Is the muscle stiff?  Is it protective tension?  These are all things that need to be answered before coming up with a game plan.  Either way, you need to get your functional range back.

Keep R high by taking a chill pill.  But seriously, here are a few ways to attack R.  First,  be sure to foam roll because it helps improve muscle tone.  Second, do some focused breathing drills (crocodile breathing is a good example).  Third, find a release that helps you relax.  For me, it’s reading fiction.  I do it every night before bed.  For you it may be having a glass of wine.  I don’t know.  Just find something.