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Law of Repetitive Motion

-Chronic injuries can be a real annoyance. I often get asked what keeps causing a persons injury to flare up and never seem to go away. That patient will usually tell me they didn't do anything that should have caused an injury. It is then I tell them more about the law of repetitive motion and the cumulative injury cycle and how that can contribute to back pain, neck pain, headaches, tennis elbow, plantar fasciitis, and a host of other problems. 

Here is the law of repetitive motion:I=N*F/ A*R where:

I - degree of insult to the tissue as caused by friction or pressure

N-Number of repetitions of any action

F-Force or tension of each repetition as a percentage of the maximum strength            

A-Amplitude of each repetition

R-Relaxation time between repetitions, a time with no pressure or tension on tissue involved 


Now you're probably thinking that great doc but what in the world does that mean? Its actually pretty simple. The insult or damage to your body is a direct result of the number of repetitions of any action multiplied by force of each repetition divided by the amplitude or how large of movement multiplied by how much relaxation time there is between repetitions. Lets look at an example that might help clear this up a little. An acute injury might occur from lifting a really heavy weight just a couple times because the force or tension is so large even if you allow a lot of time in between lifting the weight. A more cumulative injury might occur from an activity such as cycling or running where there is a large number of repetitions with very little relaxation time between repetitions. So even though there is no large heavy lifting or sudden insult to the body those repetitive motions add up to equal a large insult to the body. Okay great you're thinking that is how marathon runners and ultra cyclists can get injured but what if I don't ride my bike 100 miles per week? Well in fact it is more common for chiropractors to see injuries from sitting and typing for hours or standing bent over a counter for an hour. Those activities also involve constant contractions of the muscles in your spine and have very little if any relaxation time between contractions. 

So what should be done about these injuries and how can I prevent them? Well first off it is important to have the spine subluxation or misalignment free. Those subluxations can interfere with the biomechanics of the spine and decrease optimal nerve flow to the muscles and organs supplied by those nerves. If the biomechanics of the spine are altered the body has to compensate for that by recruiting other muscles or joints that are not ideal for that activity. So first off it is important to visit your chiropractor to make sure your nervous systems is functioning at it optimal level. Next when performing repetitive activities such as standing, bending, typing, sitting, running, cycling, ect. you take some breaks to walk around, stretch or do another activity. At least until your body is more conditioned for these tasks. 

Finally if already have found yourself with back pain, headaches, neck tension or that tightness between the shoulders that never seems to go away it is important to get the muscle back to its normal cycle. Cumulative Trauma Disorder (CTD) is a condition that is resolved very effectively using Active Release Technique (ART). ART is a soft tissue modality that is incorporated into most adjustments that I perform at Back In Action Chiropractic. ART works by breaking down fibrosis or scar tissure that accumulates in the muscles or ligaments as a result of CTD or too many repetitive movements. If you would like to learn more please contact us by e-mail at or call us at (515) 232-9075, we would love to answer any questions you might have. 

In health, 

Dr. Ben

Sources: Active Release Technique upper extremity reference manual. Second edition, P. Michael Leahy 

March 06, 2015
Team Member

Dr. Benjamin Heun