Rigidity and Spasticity: What's the Difference?

This is a question that, strangely enough, does not get asked very much...at least to me.  The reason I would categorize this fact as "strange" is that, within the context of neurodevelopmental disorders, they manifest quite differently...and with respect to their effect / affect ratios, they both present vastly different challenges.  In my estimation, the reason for this is partially the fault of the general population of medical professionals...an unintentional error, of course.  It speaks to an underlying dysfunction which I have called a "Diagnostic Disability"...which in plain terms means that the medical / health profession at large are not using the same "technical language".  Although the alphabet is the same, words are used within vastly difference contexts and, over time, essentially become merged and "blurred".  The terms "rigidity" and "spasticity" are victims of this phenomenon and therefore have essentially become synonymous with each other.  As part of the process of navigating complex physical / physiological challenges (for both families AND professionals), it is important to (at the very least) take time to provide a well-defined "glossary of terms" so that those you work with have a clear understanding of what is being said. 

The medical physiology of rigidity and spasticity are relatively complex and therefore getting into these complexities would not be a productive exercise simply because the objective of this post (and the next post to follow) is to provide a global understanding that is easily integrated and which can be built upon.  As always, information is best absorbed in "digestible" chunks. 

Within the realm of Cerebral Palsy (CP) and other disorders of movement and posture, it is important to remember (and understand) that muscular dysfunction cannot be classified into specific and explicit "categories"....that is to say, nothing in the real world is a manifestation of one pure issue.  Everyone is essentially a tangled mix of tension, stiffness, weakness, rigidity, spasticity, etc...even more so, they all overlap with each other in many ways.  To be specific, the observable MANIFESTATIONS of any and all of these issues often appears the same.  With this in mind, the pressing challenge becomes how to identify the most prominent biomechanical muscular limitation ...with the end objective being to efficiently formulate effective treatment goals as well as implement the appropriate management strategy at home (sleeping, resting, feeding, etc...).   Being able to identify is always the first step...once that has been done, the process of "what to do about it" becomes more clear and therefore results in better treatment outcomes. 

1. Spasticity is velocity dependant whereas rigidity is not

The response to passive movement is an effective way to identify spasticity versus rigidity. A spastic muscle will generally appear relaxed when at rest, but when moved passively (extended) it will increase in tone and then return to a generally relaxed state when the movement is stopped.  The rigid muscle will express high tone at rest and throughout the entire movement.

2. Spasticity, in general, involves single muscle groups whereas rigidity is global

Although not considered to be a "black and white" reality, spasticity is oftentimes found to be present in the "anti-gravity" muscles such as the hamstrings, hip flexors, biceps, etc...  Rigidity, although can certainly be found in the anit-gravity muscles, is more commonly a global manifestation.

3. From a clinical perspective, long standing spasticity leads to contractures more than long standing rigidity.

This statement is a very generalized clinical statement which simply defines some of the treatment parameters.  Contractures are always an ever-present reality regardless of specific diagnosis or classification, however a long-standing situation of rigidity tends to result in less (or less severe) complications with contractures. 


The follow-up to this post will discuss some of the theory and strategies that parents / care-givers can implement immediately.  The issue of rigidity versus spasticity becomes more multi-layered when we realize that both of these (somewhat different and exclusive) manifestations is generally addressed in the same way:  STRETCHING.  I would recommend a read / re-read of my previous post on stretching and CP to absorb / re-absorb the underlying challenges and considerations of implementing stretching protocols.  Stay tuned for the second part of this post:

"ALTERNATIVES TO TRADITIONAL STRETCHING: HOW AND WHY"

Cheers!