One of the biggest misconceptions I have to approach with most of my patients about their pain complaints and how their body works is the thought that many of their pains come from a muscle or their whole body being ‘too weak’. Some of this stems from the language used by the physical medicine world which will say this limb/muscle/etc is ‘weak.’ Sometimes what they really mean is “this muscle is unable to recruit its strength, so is functionally weaker than it should be,” and I can understand wanting to keep it simpler than this (despite the fact that I certainly never do!), as most of the industry doesn’t have the time to fully explain what they mean there. Unfortunately, they usually mean this literally because that is how most of the physical medicine world is taught. We’ll get to a simple objection to that in a minute. For now it’s important to realize that there’s a big difference between “you’re not strong enough to take a step that high” and “the ledge you’re trying to step up on is not stable, and is covered in ice, so you can’t really use your full strength to get up.” How you’d approach these two reasons for not being able to step up would be very different because so many people think strengthening their muscles is the solution, when that isn’t the problem in the first place. The same applies to a painful joint which seems to have weak muscles.
While there’s a lot to say about why the physical medicine world has gotten into this all too frequent misunderstanding, which leads to less efficient, or completely ineffective therapy interventions, I will simply use one counter argument and move onto more relevant points in the discussion. Many patients have been told that their muscle(s) are weak and that this is the cause of their pain. This assumes that for some reason strength has been lost to a degree that the body finds threatening enough to use pain as a signal to the conscious brain that something needs to change. The strength a body has is due to whatever regular activities that body keeps up. If you did a huge weight lifting workout once a year, it would not give you strength you would keep in-between these annual workouts. So the strength you have is going to be from whatever activities you keep up in your normal schedule, whether it’s exercise or gardening, walking up the stairs, and so on. The body will not maintain less strength than it needs to carry out these tasks, since by doing them regularly the brain knows that the body needs to keep the strength to do them! And it will not develop more strength than its regular activities demand.
So if you’ve walked into a PT clinic and are told that your pain is caused by not being strong enough, the first question is...have you significantly lowered your activity level lately? If you’ve had a cast on a limb for weeks, or were bed bound for weeks due to an operation or illness, the strength loss is unsurprising and all you need to do is get back to normal activity for it to come back. If you have not lowered your activities lately, this means that the strength loss, if present, is a symptom, not a cause. If your car keeps getting low on oil, do you keep topping it up and assume you’re solving the problem, or do you figure out if it’s burning or leaking oil and fix that? This is the situation if strength loss is actually a problem. Simply ‘topping off the oil’ by doing strengthening exercises is not a solution, but a symptomatic stop gap at best. Putting the extra work on a system where it’s losing strength can actually make things worse. On top of this, it takes A LOT of strength loss to create an actual pain situation most of the time. It is exceedingly rare to have pain come from a loss of strength without a medical condition really being the culprit, other than the pain of suddenly ramping up activity like going from being a sedentary desk worker to running a marathon without working your way up to such a distance.
So outside of these situations where there is actual strength loss, from a medical condition or convalescence, our remaining situations are almost always a lack of ‘strength recruitment’ causing problems, not a lack of strength. What I mean here is that you definitely have the strength for normal tasks in your regular routine, but your brain has decided it is not safe enough to do so. This is because the brain only lets the body recruit the strength that it can safely stabilize, which generally means being able to hold joints in their appropriate position to direct force wherever you’re trying to use it, whether this is pushing a door open or throwing a punch, because if that force instead is directed through a joint capsule because your shoulder dislocates...you now have an injury that will take months to heal.
In severe situations we see the brain let these governing safety mechanisms relax like a mother lifting a heavy object off her child, or a person otherwise being in a life or death situation. In these contexts, the brain doesn't have the luxury of trying to avoid injuries. On the other side, if you’ve torn a ligament or broken a bone, the muscles in the area will not be able to activate normally at all, and not just because it hurts so you’re avoiding it. These are more severe examples, yes, but they show that the strength that you own, and what you can ‘deploy’ are two different things. One is absolute, the other is contextual. Like the amount of money you have in your bank account is a specific number, but maybe you have spending or withdrawal limits unless you go into the bank and close it out.
This dynamic nature of strength recruitment applies in all situations, day to day. One of the easiest examples is showing that you can lift the most maximal amount when using a bench press machine: the bar you’re pushing on doesn’t move except up and down, and you’re planted on the bench. Switch to a barbell and now you’re planted but the bar can move and has to be stabilized so you can’t lift as heavy a weight. Switch to dumbbells and because the stability needs of controlling their position in space while you lift them is higher, your ‘strength’ goes down again. Now take kettlebells and hold them upside down (the bell above the handle) and your ability to lift has dramatically decreased! But your strength is the same...the body has simply been limited by a brain that knows it can’t safely use all of its strength as the stability demand goes up.
So let’s connect this to an actual situation that may come into my office. Let’s say a patient comes in with pain on and below their knee cap. They have patellar tendonitis: an irritation of the tendon of the ‘quads’ on the front of their leg, attaching to their shin. This is a fairly common situation. If we check the ‘strength’ of their quads, functionally they’re going to be horrible. Sometimes the patient won’t even be able to hold their leg up under its own weight. The lack of quad function may be allowing the shin bone to shift in relation to the femur, with bad tension relationships going through the tendon and a growing irritation over time until there’s severe pain. But is it a strength problem, or a recruitment problem? In my years of practice, I have yet to see this being a strength problem, for the reasons we went through above.
If the person was just getting out of a long hospital stay, not moving for maybe weeks, they wouldn’t be moving around enough to develop patellar tendonitis. As they start moving again, fatigue would realistically keep them from moving too much to develop the tendonitis, and during that time their strength and endurance would be returning.
Our easiest approach for checking that this is in fact the situation for a patient, which is often one of my first demonstrations to my patients while going through this process, is while we check their quad strength I hold down on the hip bone above the muscle and make sure it’s secure against the table. Suddenly, they have good use of their quad when they didn’t a moment before. They have enough ‘strength’ to usually hold a good 20 pounds with the leg fully extended, in addition to the weight of their leg (even a 5 foot tall 80 year old). Suddenly their strength has increased! No, their strength is the same, but now that we’ve braced their hip (without touching the muscle itself) their brain feels safe enough to use the full strength of their quad because the leg and hip are now ~100% stable. We then can brace something higher up above the hip, rechecking the quad ‘strength’ each time to see what part of the body the brain does not feel is stable enough to allow it to conduct force. A common culprit would be an abdominal or spinal surgery, like a C-section or spinal fusion area which has previously endured considerable trauma, so the brain is unwilling to allow whatever muscle or tract of tension which is putting force through this unstable area to function normally.
This process lets us prove it’s not a strength problem, but instead a stability problem where the brain has decided using normal amounts of strength simply isn’t safe enough, and then we track down and fix the reason why that’s happened. This is all so important because the vast majority of the time, pain happening because of strength loss alone simply doesn’t make sense. If it did, most of the time we wouldn’t need to seek medical care, we’d just need to work on being more active and the problem would go away. But for people in pain, as they’ve tried to get more active their pains often increase, new ones pop up, or actual injuries occur. Sometimes the pain does reduce, or even go away, but not because of the strength gain; because these repeated demands put on the body can allow the brain to figure out how to compensate around the problem in the absence of the problem being dealt with. But this is less common than causing more problems!
So, long story short, strength deficits only pop up because of lack of use, or some other condition leading to ‘wasting’ of some kind which needs to be addressed, which makes the strength loss a symptom and not a cause. In the vast majority of other situations, the problem is that the brain has decided there is a big enough threat present in using your muscular strength in the amounts needed for normal situations without some kind of significant compensation and over time it overloads or causes injuries, and becomes noticeable as your brain sends out a signal for something to change. So we work to get to the root of this problem, so that our patients can get back to a fully functional, pain free life. Strength is rarely a problem by itself, where what’s really happening is a ‘strength recruitment deficit,’ due to the body not being able to safely stabilize enough to use a normal amount of strength. We have to work on the source of the problem, instead of treating a symptom like it was the cause.