Yes you heard me right, strength is not stability! forget what you've been told because its a bit more complicated than that.
As students of the human body or as physical therapists we will all definitely be used to hearing the word ‘stability’. I hear it all the time both in the justification of treatment prescribed by professionals and across the web.
Well stability is a very important concept and the reason our bodies are so amazing at adapting.
Despite the word’s widespread use, what comes to our mind when we think of stability might not be as accurate as the hefty load of research and science behind the subject! It’s funny because the term hasn’t even been defined yet!!! Furthermore I feel we have a tendency to just stretch and strengthen things without really delving into the science and our top researchers have something to say about that too.
The term "stability," as used in the field of biomechanics, remains undefined in many clinical cases. This fact can impede the design of therapies intended to enhance joint stability - Stuart McGill
“The simplistic model of thinking that if something does not move well enough, it is tight and needs stretching or it is weak and needs strengthening no longer holds the answer to mechanical dysfunction” – Comerford 2001
“Orthopedic protocols often treat poor stabilization as a strength problem, exercising muscles associated with poor stabilization waiting for strength to occur—assuming strengthening would somehow improve timing and coordination.” –Gray Cook
Clearly the the concept of stability Is important. Actually very important!! And how poorly it’s understood is one of the possible reasons why the world of physical therapy is falling behind. As Shirley Shaarman puts it, physical therapists have a tendency to use popular treatment modalities be it needling, laser, acupuncture, massage, myofascial release in the attempt to solve injuries. But as we know these popular tendencies come and go and always will wherever the tide goes.( think of the kinesio taping craze recently ) The problem here is simple, without addressing the underlying movement dysfunction we are doing nothing to get to the root cause of the problem, so how can we expect to properly treat injuries if were just attacking symptoms with lots of gadgets?
Well if it’s so important why is there so little understanding in the world of rehabilitation? Maybe it hasn’t been explained properly yet, but to truly understand the human body, you need to understand movement and if you want to understand movement, you need to understand stability.
Recently, I came across a hefty research paper in 2001 published by Commerford and Mottram that gives a complicated yet understandable overview of the subject. Instead of writing an essay here, I’ll give a summary of the important concepts of stability and provide a few examples to illustrate my case.
To begin our discussion we need to remind ourselves what stability is and what it definitely isn’t. As previously mentioned, to date there has been no definitive explanation of stability. Despite this we know what stability IS NOT.
Stability is not strength! I repeat stability is not strength! This is the biggest misconception about stability and is something I hear so often. “Were going to strengthen the muscles and add stability”. NO This is grossly over simplified and promotes an idea that something is broken which needs fixing. So when you see a skinny muscle or a large muscle don’t automatically assume it’s either unstable or stable
So what is stability then? Well since there’s no agreed upon definition for it I’m going to do my best to describe it.
“STABILITY IS DYNAMIC NOT STATIC”
Stability is roughly described as the functional control over individual or multiple motion segments(joints), The degree of stability at a motion segment, at a given point or period in time, is measured by comparing it to the supposed ‘ideal’ positioning of the respective joint. This ideal is believed to the balanced, efficient and neutral positioning of the joint around its instantaneous axis of rotation. Stability is maintained by the various dynamic inputs of the movement system, which include the musculotendinous, nervous and ligamentous system. In addition to this, stability may also be described in the literature in the following two ways.
There are three main systems of stability, the active system, the control system and the passive system. These systems refer to the musculotendinous system, the nervous system and the ligamentous system respectively. These three systems work in harmony to control joints, maintain stability and prevent aberrant joint behaviour such as shear or abnormal translation.
Musculotendinous system: The musculotendinous system, the active subsystem of stability achieves stability through joint stiffness. Joint stiffness limits excessive motion and prevents the joint from excessive shear or abnormal translation.
Joint stiffness is produced by the individual contraction of muscles. The amount of contraction necessary to maintain stability depends on the task, in most cases the larger the load the joint has to handle the larger the contraction. Although there is a limit to this and too high a contraction can actually impose dangerously high loads on the joint, In fact maximal joint stiffness can be achieved with contractions as low as 25% of the muscles maximal capacity, these low contractions are high enough to provide stability but low enough to allow necessary mobility to the joint too.
To Use an example of the spine, functionally, the full stability of the spine requires a neutral positioning of the lumbar vertebrae and only a modest contraction of around 10% in the surrounding musculature. Thus if stability requires an ongoing contraction, this contraction is less about the individual strength of the muscles involved and more about the endurance of the muscles. This applies to most cases of body stability and a little bit less so during dynamic stability.
To maintain stability in the body, when gross movement is occuring, the musculotendinous system, is believed, to need the following components of the muscular system to be balanced in (i) length, (ii) strength (ii) synergist/ antagonist function (iv) relative stiffness (v) balanced use of stabilisers and mobilisers.
Nervous system: The nervous system is the control subsystem of stability. Maintaining stability in the body requires that the force, timing and duration of muscular contraction be precisely coordinated and calculated. This co-ordination requires an ongoing input from both the proprioceptive and motor control system. The outputs from the motor control system are based mostly on past experiences developed from previous movement strategies, and dictate the employment of particular movement patterns. Remember that the motor control system dictates movement not individual muscles. The proprioceptive system, is the body’s conscious awareness subsystem. It serves to provide feedback regarding the current external factors affecting the muscles, so that muscular contraction can respond quickly and adequately. External factors include the joint position sense, kinesthesia and sense of resistance.
Without co-ordinated muscular contraction, control is next to impossible because under and overpull from certain muscles will result in abnormal translation. Abnormal joint control due to nervous system disorders are easily recognizable in disorders such as cerebral pausy, spinal cord injuries or down syndrome. Previous injuries to the musculoskeletal system can contribute to changes in the nervous system particularly motor control strategies and or proprioceptive awarness. Changes to the motor control system post injury can result in adaptive movement strategies or maladaptive movement strategies, both have been covered in the literature extensively.
An easy way to visualise the nervous system is by imagining an orchestra. Imagine the nervous system acting as the conductor and the other elements of stability are the groups of players. If the individual groups of players were to play by themselves, there would be a catastrophe and the orchestra would fall apart and result in a poor overall sound. But when the conductor is directing the groups of players correctly, they begin to play in harmony and the finished song will sound appropriate. In physical therapy a lot efforts are directed solely towards strength changes in the hope that these will have effects on motor control strategies, but this could not be further from the truth, strength training will have little to minimal effects on motor control strategies, changes to the motor system need to be addressed through focused proprioceptive training. Strength work in the hope that it will affect the motor control system is akin to a group of players doubling the volume and hoping that the orchestra will sound better.
Ligamentous System: The ligamentous system is the passive subsystem of stability. The ligaments contribute passive stiffness to the joint and thus stabilize it. The degree of stiffness the ligaments contribute increase towards the boundary of joint motion.
Disorders occurring to the ligaments are detrimental to stability and can lead to an earlier onset of pain or at worst arthritis. Examples of such disorders are ligament laxity syndrome, partial or complete ligamentous tears. These pathological changes are unwanted changes to the stability system, the restoration of such changes usually requires surgical or regenerative procedures.
A common injury occurring to highly mobile athletes such as dancers or gymansts are in the knee and hip. These athletes tend to have disorders involving the ligaments, since the ligaments have become relaxed, they fail to provide a passive tension to the joints, thus it is more common for these type of athletes to suffer from soft tissue and joint capsule disorders later on. Because of this inherent instability that goes along with these type of sports, better motor control strategies are essential and have been the subject of some research recently.
Similar to stability, Instability presents as either an individual or multi-segmental problem. Dysfunction around a motion segment reflect through a combination of restriction( lack of normal range of motion) and give(compensation) in order to maintain function during given movement tests. The movement inadequacies may or may not be accompanied by motor control changes and pain but in a lot of cases are. The issue of instability is that the associated muscular changes may cause an overpull and under pull around a motion segment, which results in displacement of the instantaneous axis of rotation placing the joint in an abnormal inefficient position. This excessive joint motion increases the micro trauma around the tissues which, overtime can lead to pathology. Instability is most often accompanied by a lack of control of a motion segment.
Pain produced by unwanted changes due to alterations in the biomechanics of the body are more likely to have an insidious onset, compared to other traumatic events which may pass overtime. Movement dysfunction and instability are interlinked and generally follow a cycle beginning with restriction and ending in pain.
Cycle of Instability restriction – compensation – give - pathology – pain
Restriction, the initial cycle of instability usually develops from poor movement habits or poor posture.
Both the motor control and muscular changes which arise from instability and movement dysfunction are thankfully reversible. Rehabilitations programs aimed at restoring stability require specific postural re-education, specific strength training, myofascial release/mobilisations, proprioceptive focused training in an attempt to improve motor control and co-ordination
Its clear that stability, instability are compiled by a complicated set of inputs, thus rehabilitation requires specific knowledge of all three systems In order to achieve the desired change in pain/dysfunction.
Here are a few examples of instability and why the conventional approach might not be as appropriate.
Patient A: Patient Adam an amateur basketball player suffered from a badly sprained ankle about a month ago. Only today has Adam been given the chance to take off the cast. It is clear the ankle has lost a lot musculature due to atrophy. Adam is currently not in pain and is due to leave the hospital but needs to undergo rehabilitation first.
Upon examination, Adam has rated poor on balancing tasks. His trunk experienced considerable wobble and the ankle was easily rocked or imbalanced.
In response to the poor balance test, the rehab professional prescribed specific strength training to the ankle using resistance bands and body weight excercises such as calf raises. They also prescribed a core strengthening regime including planks and side planks to address the core instability. The rehab professional is of the opinion that this will help Adam prevent the injury from re-occuring. Unfortunately on return to sport Adam suffered another sprained ankle.
So why did the injury re-occur? Well as we know, maintaining functional stability at the ankle is the outcome of multiple inputs. So simply addressing the muscular component is trivial unless the motor control strategies are addressed as well as the ligamentous system.
It is clear from the balancing tests that the motor control strategies are poor, whether this is as a result from the injury or was present before the injury isn’t important, what is important is the fact that it is a maladaptive strategy and no doubt will lead to another injury.
Specific neuro muscular training is necessary to reverse the changes of the injury.
In order to rehabilitate the instable ankle, it is required that the training be Task specific, Proprioceptive, repetitive, dynamic and conscious. These terms don’t really mean that much on their own but are concepts which must be incorporated into the training program
An example of an exercise would be a one legged balancing task on a balance disk. The patient must control his or her centre of gravity while simultaneously responding to the stimulus. An example could be a ball being thrown at them. Progressions may start with the use of support via a chair but ideally no support should be used. Conscious controlled positioning of the joints is fundamental to the task , Ensuring that there is no internal rotation at the femur or collapsing of the arches is essential to preventing a sprain. The use of a mirror may help with this. Repetition is key when it comes to motor control training. The desired conscious movement must be imprinted on the nervous system so it becomes an unconscious movement pattern and thus a protective one.
Ligamentous system- Since the ankle has been completely immobilised, it is likely that the ligament affected has lost its tensile strength and the collagen has become disorganized as well. Specific eccentric training would be necessary to return the alignment of collagen and return the tensile strength.
Similarly , ITB band syndrome is a nasty injury and one that is likely to re-occur. We know that subjects with this injury can get a lateral translation or shift of the hip during the single leg stance of the running cycle. This tensions the Ilio tibial band and pulls on the lateral aspect of the knee. We also know that the hip is weak in ITB band sufferers. So clearly the stability of the hip is compromised.
So what do we do? Should we just prescribe hip abductor exercise’s and hope we will add stability to the hip? Well that’s what some people do! But yes strengthening isnt a bad thing, but how do we stop the hips from shifting is the real question? It doesn’t matter how strong your hips are, as long as your movement strategy is faulty you aren’t going anywhere. But now we know that the motor control system is half the pice of the pie and needs addressing.
So I came up with a little innovative strategy using kinesio tape. Start retraining slowly but be mindful of the level of your hips, this is easier said than done so here’s a great way to give you real time feedback. Apply tape in an upward direction, and start from a little bit below the greater trochanter of the femur and end a few inches above your iliac crest. Every time your hip shoots down, you’ll feel a large pull on the band and can adjust your running form accordingly. This in essence increases the proprioceptive feedback which you can then use to stabilise your hips correctly.
So that's all for today, hope you enjoyed the article.
Caolan here. Im a curious man to say the least and as an enthusiastic enrolling physiotherapy student. I have felt the need to share my thoughts and conclusions on the topic that is pain. Its something that will effect us all. Above all its very mysterious, misunderstood and complicated one and Im here to figure out more.