Some issues to consider with a strength assessment for low back pain

Strengthening exercises seem to be getting more popular and making a bit of a comeback for musculoskeletal pain conditions, including low back pain. This is despite the considerable body of evidence showing small treatment effects; or a clear mechanism of benefit. It isn't actually known why strengthening can help low back pain and it is isn't clearly known who will be harmed or who will benefit from strengthening.  

Another issue is the rather blind recommendation that often occurs for a strength based intervention without actually knowing if there is a strength deficit and if this deficit is relevant for the patient in front of you.

There are numerous reasons why systematic reviews can be incorrect. Sadly, "exercise" gets lumped in to one group. There very well may be a small subgroup that responds very well to a form of strengthening.

What strength assessment is best?

I don't know the answer. It is likely individual and logic says it should be based on the patient's functional requirements. It surely can't be a "one size fits all". Unfortunately, there are very few tests that are reliable. In any case the purpose of this post was to highlight a few key issues related to the assessment of strength in low back pain (and all musculoskeletal pain).

·         Behavioral Factors

o   behavioral factors (fear, stress, anxiety) influence motor control. Although fear of movement / kinesiophobia has been the most assessed behavioral factor and influences the results. They need to be assessed and accounted for.

·         Functional Considerations

o   As  noted above, a strength assessment is likely individual and should be functionally related to the symptoms. Is a squat assessment the best functional test for someone that only gets low back pain during prolonged sitting?

·         Sensation of Effort

o   There are several terms related to effort which should not be confused.The sensation of effort is related to how much cognitive effort (central) is required to perform a given task. This is directly related to sensory motor function (as well as fatigue). Sensory motor function is impaired in a variable manner in people with low back pain (and in other musculoskeletal pain and in the pain free population who have neurological factors such as cognitive deficits or neurodevelopmental disorders). So when someone appears to have reduced strength on a test, are they really weak? This raises the fundamental question: "What is actually being assessed during a strength test"? As well: "Is strengthening going to correct that deficit"? And is correcting that deficit going to lead to a clinically meaningful change (beyond the small treatment effects we see) in pain, disability, function, quality of life?

·         Chronic Low Grade Systemic Inflammation

o   This is now known to be the root cause of all chronic disease. It is also now known that it influences muscle stiffness / tone in at least certain populations. So the same questions raised above can again be asked.

·         Proximal Stability

o   This will be a contentious issue for many. The idea that there needs to be a "stable base" for the muscles to operate / attach to in order to generate force has been around for over 25 years. This has been widely criticized of course. One needs to look no further than the active straight leg raise test for any validity of this concept. With light pressure on the pelvis, many people report that lifting the leg is "easier", "less effort", leg feels "stronger". This concept is not relevant all the time, but may be when there is a more severe articular related presentation. So the same questions raised above can again be asked.

·         Neurological Factors

o   The upper end of the more severe sensory motor deficits noted above under sensation of effort may also be considered under Neurological Factors. But this groups also presents with reduced neurocognitive deficits, the presence of neurologicla soft signs such as widespread primitive reflexes. These neurological soft signs significantly influence motor control. Hence, this group is known to have reduced strength in a variety of tests (they respond best to a neurological based approach - primitive reflex inhibition). 

In summary:

Numerous factors can influence a strength assessment. Be very careful how you interpret the results of a test and decide to do rehab.

There is a very clear need to define a standard therapy for research so that there can be a proper "head to head" comparison

Exercise types with pictures, descriptions need to be standardized in journals to allow replication studies.

Strengthening may be a stage of rehab for some people. It isn't known if this should be first, middle, last...

Now that we know chronic low grade systemic inflammation influences muscle tone / stiffness, strengthening may be a strategy to try and counteract this. The best strengthening approach for low grade inflammation is not known. (Note: when significant LGI is present, the best approach is a dietary lifestyle approach - Functional Medicine)

https://smarterehab.blogspot.com/2019/12/modified-ketogenic-diet-and-supplement.html

Pain is complex. Simple solutions are not going to work for most people. There are many deficits between healthy controls and those with low back pain. These include numerous motor, behavioral, immune, sensory motor, neurological differences. A comprehensive sub-classification based approach is required. With a hierarchical  and concurrent approaches to address the individual presentation.