Load vs Capacity: the good and the debatable


By Kevin Maggs @RunningReform

Two weeks ago, I released a video called “Load vs Capacity”. The ideas were not mine, but they were presented in a way that could be understood by patients. The video was well received on social media. So well received, in fact, that I did not come across any counter arguments, and I find that highly unusual in the current social media environment. While I’m happy that it was so widely accepted, I also enjoy debates. Since I didn’t come across one comment that challenged the ideas in the video, I would like to take that opportunity here. In this blog, I’ll write about why I made the video, and then talk about the good and the debatable points of Load vs Capacity.

The WHY: 

The general idea behind Load vs Capacity is pretty simple: All tissues have a certain capacity and if the mechanical load applied to those tissues is greater than their capacity, there is a higher risk of pain or injury. This is likely dose dependent.

To start off, I have to thank Greg Lehman (T:@GregLehman), Ben Cormack (T:@CorKinetic) and others who have taught me to not allow the pendulum to swing too far to the psychosocial side or the bio side in the Biopsychosocial model. A few years ago, I became an instructor at The Running Clinic (T:@ClinicRunning) a reference centre for the prevention and treatment of running injuries with courses that emphasize the load/capacity relationship injuries mentioned in the video. While teaching continuing education courses to physiotherapists, chiropractors and podiatrists, I quickly realized that the majority of healthcare providers are still very heavily married to the biomedical model. It was often difficult to break to these health professionals that kinematics and kinetics aren’t as big of an influence on running injuries as they have thought they were.

As a chiropractor in my own office, I became tired of picking battles with patients who were convinced that a short leg or a vertebra out of place or an arch height etc. was responsible for their pain and injury. A seed had been planted in their minds from almost every healthcare discipline: medical doctors, podiatrists, physical therapists and chiropractors. Confronted by the same wall over and over, I found it easier to gather my thoughts and make a video that reinforces the ideas that I share with my patients.

The GOOD in the Load/Capacity Model:

(1) It’s empowering! Patients are often discouraged or completely defeated because they have been told that they have some anatomic peculiarity or biomechanical ‘flaw’. This feeling is exacerbated when a patient sees imaging that shows tendinopathy, a tendon tear, a degenerative spinal disc issue or cartilage degeneration. Patients are made to feel like they have no power over those things and lose confidence in their own abilities. Sometimes patients are told to stop running, stop lifting weights, and protect the injured structure.

The Load/Capacity Model teaches patients how to adapt. If you gradually apply load, your body adapts by increasing capacity. Unfortunately, reducing load, (a sedentary lifestyle, or over-protecting an injury) leads to reduced capacity. A better idea is to have a graded exposure to load whilst monitoring symptoms in an effort to increase capacity. This creates self-efficacy and an optimistic mindset, rather than one that breaks a patient’s confidence.

Here’s an example: a patient with years of chronic or recurrent lower back pain has been told to protect their spine. Therapies have included soft tissue work, electrotherapy, stretching, ultrasound and injections. An MRI shows disc degeneration. Since the patient has been told by healthcare providers that their spine is degenerating, they become discouraged and afraid that if they move wrong, they will get hurt. The emphasis is on protection, which reduces capacity further. Contrary to instilling fear and victimization, the Load/Capacity model explains to the patient that they can actually increase the capacity of the tissues if we take an approach of graded exposure and rely on adaptation of the tissues. This helps the patient understand that there is hope to actually increase capacity and function, which is empowering for the patient.

(2) Versatility: the principles of Load/Capacity throw a wide blanket over every injury and a lot of pain experiences. It can explain why someone got injured, it can help another person rehabilitate and return to play, and it can also help prevent future injuries by encouraging a patient to maintain a constant load, thereby possessing a higher capacity to resist injury.

The Load/Capacity model can help a patient understand why they got injured. This could be a result of changes in load such as trauma, overuse injuries, or sudden exposure to a new environment like a new office chair or new running shoes. It can also include situations where the load may be the same, but lowered capacity is occurring because of poor sleep, poor diet and other environmental stresses. Not only is this valid for explaining “why” people have injuries or pain, it can also explain how to get out of pain, as outlined in the above example (under the ‘it’s empowering!’ heading).

Lastly, the Load/Capacity model is wonderful to encourage patients to maintain some mechanical load on their body. By doing so, they can keep the capacity of the tissues higher to mitigate the risk of overuse injuries, arthritis and a myriad of other morbidities and mortality. This is better known as Exercise is Medicine.

Now, onto the DEBATABLE:

(1) Simple does not mean easy:It’s so simple!” and “It’s that easy!” These are comments made on social media about the video and the principles of Load vs Capacity. Yes, on the surface, it is that simple. But when you try to determine how much of an increase in load a patient can tolerate… It’s not that easy. For example: how do we quantify “too quick” of a change? How do we quantify how rapidly we can add running speed vs. mileage? What about changes in footwear? Or changes in technique/biomechanics and changes in surface?

To complicate matters, it’s not only changes in load that we must think about, it’s also the capacity. How do we know what a person’s capacity is? We must consider age, smoking habits, diabetes, medication (statins, cipro etc.), previous injury, genetics, diet (RED-S) and many other factors. Not only should we examine these variables between different people, we also need to ask what changes have occurred for that person (sleep, stress levels etc.). 

When you need to consider so many factors and then give recommendations to a patient, it turns out to be not so simple after all. And don’t expect to see an answer in the literature. With so many confounding variables, it would be impossible to come up with ingredients and a recipe for this. This is where being a healthcare provider turns into an art and not just science:  there’s a need to blend sensible decisions based on education and knowledge with professional judgement. 

(2) Maladaptation: for the most part, we know that our bodies do well at adapting to loads.  Tendons seem to have a left/right asymmetry in morphology and properties depending on the jumping leg. Humeral retroversion is an adaptive process in overhead throwing athletes. The list of different structures that have a healthy adaptation to load application is lengthy, and we view this as positive, but there are also maladaptations. The best known may be the increased risk of femoral head-neck deformity that is associated with FAI in those who participate in high level youth sports. The normal, logical osseous adaptation that occurs in response to mechanical load appears to lead to higher risk of symptoms later in life.

Taking the debatable points into consideration, the general premise of Load vs. Capacity is certainly one that trumps that of the pathoanatomic or kinesiopathologic models. The confidence it gives a patient to manage their injuries is invaluable. Patients can leave clinic understanding that they can gradually work back to a state of health instead of blaming their function or anatomy. It encourages people to avoid a sedentary lifestyle because they now understand that capacity is unavoidably married with mechanical load, and that injuries are associated with capacity. They are now in control.

Let’s talk about this more. What are your thoughts? Tag me in them @RunningReform.

PS – If you missed it, the BJSM team re-posted my video on their YouTube channel, you can watch it here:

Kevin Maggs (@RunningReform) grew up in Canada and is currently a chiropractor in full time practice in Gainesville, Virginia. He is director for the USA division of The Running Clinic (a BJSM approved organization) and is a speaker for The Running Clinic’s CEU courses which can be found here: https://therunningclinic.com/en.

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