The Bell Curve, Outliers, And Health Care

In my last post, I discussed how the bell curve could put a lot of training myths and fallacies to rest. But if you think that the outliers dominate training and fitness, wait until you look at their effect on health care.

In health care, and most certainly in the sports medicine world, clinicians continue to believe that symmetry and alignment are critical in the discussion of injury rehabilitation and prevention. In the same breath, there are countless clinicians (be they physical therapists, chiropractors, massage therapists or physicians) that go on to describe biomechanical mal-alignments and “imbalances”, and then spend their lives trying to treat patients that present with these “syndromes”. In their minds, it is obvious: that which is not symmetrical must in fact be a cause of your _____ pain (insert any typical musculoskeletal complaint here).

I never cease to be amazed that the human species has survived thousands of years with the scourge of the dreaded biomechanical mal-alignment. Wow. It is hard to believe how we, as a species, could ever survive a quarter inch difference in leg length as we ran through the jungle, or how we didn’t die of neck pain given that one shoulder was higher than the other.

Let’s go back to our friend the bell curve. How about a brief reminder: two standard deviations on either side of the mean – considered by many to be “normal” for anatomical variations – encompass 95% of the population. That leaves 2.5% of the population on either side of the curve as “outliers”. When it comes to anatomical variations and their relationship to pain, there are those on the far side of the curve that have horrible alignment, yet function normally and have no problems from cradle to grave. There are those on the far left side of the curve that have horrible problems yet have pristine alignment. If 95% of the population are considered “normal”, does an asymmetry predict pain or loss of function? The scientific literature would indicate a resounding “no”.

Health care providers spend countless dollars on treatment of “imbalances” and “mal-alignments”. It could be via exercise, orthotics, or a variety of treatment approaches. But if you are basing your treatment on the 5% of outliers that have biomechanical mal-alignments that are actually relevant to the onset of their symptoms, you are missing the forest for the trees for the 95% majority.

The human body adapts to the imposed demands of living and training on planet earth. Astronauts sent to space adapt to the altered demands of gravity with a decrease in muscle strength and bone density. Why? They no longer require it, thus they adapt to the demands to remain functional. When the same astronauts return to earth, they (again) adapt to the greater demands by re-gaining muscle strength and bone density. Why? Because if they didn’t, they wouldn’t survive the battle with gravity.

Human physiology is designed to provide immediate feedback – typically in the form of pain or loss of function. It doesn’t wait 30 years to tell us that something is wrong, perhaps related to that little mal-alignment that has been there since the dawn of the patient’s life on the planet. Humans are, by definition, “in balance”. Physiologists call it “homeostasis”. So while we have, for years, made many a hypothetical quantum leap about alignment and symmetry and pain and function, we still need to be reminded that the body will adapt to the demands imposed on it, and what we see right now – symmetry or otherwise - is simply a snapshot (in time and space) of the body’s current adaptations.

Perhaps the reality is that the range of values within the 95% are simply varying levels of adaptation. The vast majority of the problems we see need to be addressed simply by understanding how the body is responding to mechanical loading and providing the body with an environment in which it can attain homeostasis and self-regulation effectively. It will adapt to the demands of the world we live in given an appropriate environment in which to do so. Pain and loss of function are simply reflective of the body’s current inability to adapt to the imposed demands, and not because of asymmetry or imbalance.

Though the outliers may dominate the belief systems in training and in health care, the long-term solutions lie in the middle of the bell curve: the physiological reality for the majority of the population. Effective health care needs evidence-based principles and mechanisms that apply to all – not just the outliers.

Photo credits: Wikipedia