Strengthening the most overused term in rehab?
How often have you heard a therapist or trainer say to someone in pain “you need to strengthen XXX, go and do 3 x 10 of XXX exercise” as the panacea to the problem.
You can replace the ‘XXX’ with the core, knee, hip or other component of the anatomy that have been touted as the cause of pain. This can include the TvA, glute med, VMO or other ‘magic’ muscles and the associated 'therapy' exercises to get them going.
My personal issue, and I accept this may just be my issue here, is that I think the term ‘strengthening’ is bit vague, often ambiguous and many times not relevant to pain.
I want to start off this little piece by pointing out I am not saying strength does not matter, its just that we could do a little better with understanding the specifics.
Like most things to do with the body, strength comes in many variations that need to be applied to the individual and their situation.
This also does not mean that special ‘therapy’ exercises cannot have an effect on pain levels, we know pain can wax and wane according to multiple factors. A decrease in pain just may not be to do with an increase in strength or the fact someone was weak to begin with!
Does the ‘strengthening’ mindset also ever so slightly imply that pain is just simply to do with a ‘weak’ muscle or an associated biomechanical factor, something I am not so sure about given our improved modern understanding of the complexities of pain. After all strong people still do get pain like all the rest of us.
The real purpose of the piece however is just to consider the term strength and the concept of ‘strengthening’ a little more in the rehab process.
So what does ‘strengthening’ really mean?
There seems to be a couple of meanings for strength depending on who is using the term.
One definition is to “exert force against an external resistance” - being strong enough to move a weight for example. We generally quantify this simply by the weight of the load being moved.
This definition would be the traditionally recognised one in strength training circles.
It seems another definition used, perhaps more in a therapy sense, is to be able to "tolerate a force". So a runner may need strong muscles to be able to tolerate the repetitive ground reaction forces involved with running.
Straight away it would appear we have an ambiguity with such a commonly used term.
There do not seem to be many runners that do not have the basic strength to exert the amount of force or the ability to tolerate the peak forces involved with running. It seems to be much more about the toleration to the repetition of that force and how frequently it is applied.
Similarly another example is that there probably are not many people, and that includes people with back pain, that don’t have the basic core strength to create adequate ‘spinal stability’ when they are not in the most acute stages of pain.
The first definition implies that we need to increase the amount of force we can generate. The second would be tolerating a specific level of force repetitively.
Congruence of what we mean by ‘strength’ and ‘strengthening’ and how we subsequently assess and rehab ‘strength’ must be fairly important right?
In an ideal world this reasoning would then translate into the exercises, loads and sets and reps thus creating (hopefully) a more applicable rehab plan with a better outcome.
So which one did they mean mean?
Frankly who knows! Personally I think of strength generally as the ability to generate force so when I hear the term ‘strengthening’ my first thought is how much force does someone need to be able to generate to not be in pain?
Some of the other questions that pop up are:
- Are the activities that are causing problems outside of their current level of strength?
- How much strength do these activities really require?
- Is the ability to produce or tolerate force the issue?
- What is a ‘healthy’ level of strength and does the individual achieve this?
- Is it strength or skill/coordination?
- Are strength deficits (if they are present) a cause or a result of pain?
- Has a ‘strengthening’ program actually increased strength?
There is the very real possibility I am over thinking it though!
Application to exercise
Lets take a common hip strengthening exercise such as a ‘side lying hip abduction’ (quite a mouthful) a staple for a runner with knee pain.
Now if someone could only do say 5 or 6 then I would certainly say that this was a strength exercise for them. If they can easily bang out 15, which I have often seen, then I would suggest they have adequate strength and this exercise may not then improve their strength base.
The classic 3 X 10 seems to have become fairly ubiquitous and the 'de facto' rep range.
As I will discuss latter this does not mean that the exercise will not help, it just may not be because of an increase in strength.
Look at the majority of exercise guidelines/principles and we can see that this commonly prescribed rep range of 10-15 is associated more with hypertrophy and endurance rather than increasing strength. Strength is improved with a rep range of between 1-6. These of course are not absolutes and that does not mean no strengthening occurs over 6 and no hypertrophy under 6!
People also adapt pretty quickly to stimulus and progression is a key to any ‘strengthening’ program. If someone is already capable of doing multiple reps and sets then no change in the demand to produce force such as added load is unlikely to further ‘strengthen’. A further stimulus would be required to create an adaptation in strength.
How often do we obtain measures of strength pre and post exercise to see if we have actually given someone more strength and if this change in strength has affected pain levels?
This does not mean that strength training does not have a whole bunch of benefits such as increased tissue tolerances and stiffness of the tendons and muscles and even improved performance. Although the forces involved would have to be high enough to create this physiological adaptation.
3 X 10 of an exercise designed to isolate an individual muscle may be so far within someones capabilities that we don’t get the same physical adaptations as we would to a 2 x 6 reps of 70% of max squats for example.
It means that to actually 'strengthen' you need to correctly manipulate variables such as load and repetition to create an increase in strength not just do an exercise that is touted a ‘strengthening’
Input vs strength
So it maybe the process of ‘strengthening’ that could have many non-specific effects rather than simply an increase in strength being the therapeutic factor. It could be restoration of strength is a result of the affect of the therapeutic factor.
It seems collectively we are driven now more than ever to understand the why’s and how’s rather than it just ‘does’!
Is someone any stronger than they were to start with before they were in pain or has their existing strength just returned as the pain has subsided? Or it could even be that someone does actually get stronger but yet is still in pain.
Weakness does seem to accompany pain but once pain improves then strength also seems to improve as well. It could be easy to view the causative factor of pain as muscular weakness especially if linked to a biomechanical effect from that weakness such as increased hip adduction for Patellofemoral pain.
Equally though a critical thinker must also see the situation in reverse. That pain may have caused the decrease in strength.
Reducing strength when in pain makes some sense to me as the system wants to decrease the amount of force going through an area it feels protective towards. The same would be true of an ankle sprain and the motor adaptation of a limp.
Movement input can have an affect on pain for many reasons across the biopsychosocial spectrum. This could be the hypoalgesic effects of movement/exercise, decreasing fear avoidance, focused input, activation of a different neurotag, changing cortical maps & different kinematics or kinetics or even just plain old father time exerting his influence.
All of these elements may change the systems perception of the problem and ultimately the sensitivity level and the pain experienced.
Here is a therapeutic movement 'input' idea for the lateral hip of a runner.
- Movement variability
- Multi planar
- Muscular co-ordination
- Control of ROM
- Eccentric and concentric contraction
- Added resistance for ‘strengthening’
- Upright & closed chain
The idea is that this low level localised movement skill is then integrated into functional running movements such as lunges, hops and running!
Strength is often measured maximally!
Strength is often measured in research circles as MVIC (maximal voluntary isometric contraction). Does this baseline measure of the maximal or even subsequent increases in strength tell us anything about what someone can tolerate or control regarding force?
Maximal isometric strength does not seem to be significantly related prospectively to patella-femoral pain or illiotibial band syndrome for example. Biomechanical measures such as increased hip internal rotation and adduction appear to have a better, although still unclear, correlation.
Exercises may also be selected on the increased EMG activity of a specific muscle. Essentially all this tells us is the muscle works harder, a proxy for strength, within the specific constraints of the exercise.
EMG does not tell us if working the muscle harder is or will make a difference to someone’s movement or pain levels. It also does not tell us that the exercise is better than another exercise for the individuals problem.
The many faces of strength
There are many sub categories of ‘strength’ that we can use to specifically suit the individual and their needs.
The most force a person can produce or withstand. A large load for 1-3 reps would affect this.
An ability to maintain a level of strength over an extended period of time, a sufficient load with an element of duration.
Reactive or explosive strength:
Switching from eccentric to a concentric contraction. This is something we see in most sports especially repetitive ones.
This would often be time dependent such as in running, throwing or hitting.
Strength speed or acceleration strength:
How quickly can force be generated, as we would see in changes in rate of force development. This is often about the A in F =MA rather than the M!
In fact max strength probably only really becomes relevant in situations where you need to overcome an object that requires this maximal strength. So say your max squat for 1 rep is 100Kg then only when you squat 100Kg does this become a factor.
If I am a rugby player then this becomes very relevant, as the loads I am looking to overcome will be much larger and extremely close to someone’s maximal ability. Some of those big guys really do take some shifting.
For our runner it may be that maximal strength maybe less important than strength endurance or reactive strength endurance. There are lots of people who have a very high maximal strength but are not great runners and vice versa.
The runner would need the ability for the leg to tolerate the amount of force being driven through the leg that can be 3-4 timers body weight on impact. This is also coupled with the reactive strength of the lengthening and shortening as we go through the gait cycle. All this needs to be performed over thousands of cycles therefore a runner will also need to have a decent level of endurance for this.
It is a good thing it is easier to tolerate a repetitive force of 3-4 times body weight rather than to generate it!
Someone with lower back pain may need the ability to tolerate more strength repetition (strength endurance) or position (positional endurance), think of the person who’s back is irritated by spending all day gardening.
Equally someone’s back may ‘go’ when they need to pick up heavy stuff such as the suitcase for their yearly holiday. This may mean they do need to work more on increasing their actual level of maximal strength.
It would appear that ACLR and Achilles tendonopathy patients recover their maximal strength much quicker than their explosive strength (rate of force development) Equally explosive and reactive strength work my irritate an Achilles tendonopathy too early in the rehab process.
In my opinion a simple exploration of the term strength and application to the current state of the individual throws up some useful pointers for how to make more relevant rehab programs.
Can strength just be coordination?
Strength can also be the ability to successfully coordinate muscle activity in a specific way. Someones muscles may be strong individually if you were to test the muscles or even perform exercises specific to a muscles as many 'therapy' exercises do. When you get them running however they do not have the ability to coordinate that strength to reduce the medial movement of the knee that you may feel is causing them trouble for example.
Muscle strengthening separate from a specific movement is in no way guaranteed to transfer to the movement or change the kinematics of the movement. As we discussed earlier in the piece however the process of ‘strengthening’ regardless of increases in strength may have an affect on pain.
People can make huge strength gains in a short amount of time when they first start with functions such as Olympic weightlifting. This in part will be to do with coordinating their existing strength into the muscular coordination of a specific skill.
Both gait retraining and ACL prevention and rehab have looked much more at skill and coordination of specific movements than simply increasing strength.
In fact hip strengthening has been shown to have questionable transfer to the actual kinematics of running.
Gait re-education may be successful for both pain and movement changes because of the specificity of the skill. This being the motor pattern and inter muscular coordination of timing, specificity of contraction type, velocity and forces involved with the actual skill of running.
There are many ways in which we can be specific with 'strengthening' and even rehab training overall.
- Contraction type
- Movement pattern
- Velocity of movement
- Range of movement
- Force of contraction both eccentric and concentric
- Endurance level
Nordic hamstring work also seems to be fairly successful and that may in part be due to with the specificity of type (eccentric), force level and velocity of contraction.
Rather than just saying ‘you need to strengthen XXX’ as a panacea, instead being armed with a better understanding of strength and when it maybe relevant surely we can develop more individually focused and hopefully more successful outcomes.
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