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Trying to Identify Performance Limitations - What is The Benefit of Physiological Testing?



Sport science has evolved greatly over the last 20 years. With advancements in technology we are able to gain greater insight into human performance. Whilst the phrase 'you manage what you measure' is true, it doesn't mean everything you're measuring is important, or even fully understood. Additionally, the accuracy of the measurement is completely dependent on the quality of the instrument and the methods being used.


When trying to identify specific performance limitations through physiological testing for example, it is a nice idea on the surface, but in reality when we dig a bit deeper, I question whether we truly appreciate the interconnectedness of the things we are actually trying to measure. I also think the importance and inference we gain from certain data points is unwarranted. In the end, if we are being honest, this is just par for the course; a consequence of the terrain we are trying to navigate. Ultimately, there are inherent limitations when we try to partition physiology into neat boxes using math or rules of thumb. Physiology is not math, there are systemic and remote responses to exercise, all that happen in a blink of an eye to serve things from muscular contraction to whole body homeostasis.... (insert Matrix reference... you still think you're seeing, what you think you're seeing?).

We have to have some transparency about it's utility. Besides, when looking at the bigger picture here, for most of us who aren't the elite-of-the-elite, we should be cautious about WHY we are testing and WHAT it is we are actually hoping to find. As an old coach of mine used to say...'

"Why look under the hood of a Nissan Micra? We're not fine tuning performance cars over here - just get to work".

A more subtle way of saying 'you're not special' so why spend time trying to zoom in to the specifics anyway?


Most people don't need physiological testing to highlight general areas for improvement. I might be harming the pocket here, but current training and previous training will probably tell you what you need to know for most of us. That is, spending time doing these tests, and then trying identify potential limitations when EVERYTHING is probably a limitation is just a waste of time. If someone is very new to deadlifting, do we really need to test them to their maximum deadlift? And then also figure out at what point in the lift they fail at, and with what specific muscles are perhaps limiting them? Not really. It won't illuminate anything groundbreaking.


This perhaps is a bigger issue in many peoples mindset & approach to training in general. We crave instant gratification, and that leads us to seek out the next best thing. The tool that will fast track us. We want it all, and we want it all as quick as possible. Unfortunately this is not how it works. Perhaps the unintended legacy of Sir David Brailsford and Team Sky's meticulous approach to edging out the marginal gains.

Focusing on the 1% is great.... when you have maximised the other 99%.

These ideas often just leads people to obsess over the minutia, akin to rearranging the deck chairs on the titanic. I digress... Perhaps that is another post all together.


The problem though as eluded to at the start; physiological testing often is layered with reductionism. Reductionism is the practice of analysing and describing a complex phenomenon by its simple constituents, said to provide a sufficient explanation. Science as a tool, specifically in its application of investigating the human body, has been primarily driven by philosophical reductionist tendencies i.e everything has a cause, we identify the problem, we treat the problem. There is of course been valuable understanding gained from this approach, and will continue to have some value in terms of things like risk reduction. But often, as written by academic and science writer Ben Goldacre, "it's a bit more complicated than that". A problem in a complex system (like the human body) rarely exists in isolation, triggered by a single factor, a cause. Even with something as well established as the link between smoking and lung cancer, there are other co-factors which influence outcomes. X behaves differently if X-Y interact, which behaves differently if X-Y-Z interact, and so on. So the information we gain about individual parts is usually insufficient to explain the whole.


When tasked with trying to improve an athletes physical performance for example, we often look to find out why the athlete is limited. If we remove 'skill' from the debate (skill usually IS a primary limiting factor for most people in sport) then we are left with physiological structures. We are essentially left with biological tissues. A heart. A pair of lungs. Muscle. Tendons. These are governed by systems within systems. Driven by a larger overriding system, the nervous system. The brain communicates with the spinal cord and everything in the periphery. All of these things contribute and play vital role in response to exercise. To get to grips with what I'm talking about here in relation to performance, lets consider first and foremost that the body simply doesn't care about anything other than homeostasis. It desires balance. What happens, without you really knowing, is seeming constancy despite continuous change. Because of this, and put simply... the idea that anyone can isolate a specific physiological mechanism, remove it from compensatory mechanisms that keep you in check, and then confidently state "this is the very thing that is limiting your performance during exercise all of the time and the very thing you need to train"... ascertained from in a single physiological test..... is likely talking nonsense. Respectfully. And breathe.


I have run lots of VO2 max tests and lactate tests over the years, and whilst I enjoy the exploration, I am always very honest about this. The point of testing for me, for whom it is appropriate, is to attain a greater level of understanding. It does help locate a ball park of appropriateness that is perhaps more specific than without testing, and is certainly more appropriate for those who are already well trained. Primarily though, for me VO2 max testing is worthwhile in terms of intensity prescription (training zones). Essentially, all the data should be married up with what you see in training, with previous and current training trends. This then helps you build a picture of what to do moving forward in terms of training recommendations. However, as mentioned, I'm still very weary of stating a specific physiological limitation.


Lets delve deeper into the specifics of a VO2 max test as an example of this - which I should mention is still one of the best ways to measure the bodies response to exercise. Certainly far more insightful than using something like heart rate alone. A quick reminder, but a VO2 max test is considered the gold standard measurement in understanding endurance performance. VO2 max can be defined as the total amount of oxygen we take in and utilise during exercise. We ascertain this measurement with a metabolic analyser, looking at breath by breath analysis, specifically O2 and CO2 gas exchange. Through this measurement we can also understand things like fat and carbohydrate utilisation at different intensities. Essentially it is a small window, a snapshot into your physiology. However, it is still insufficient in its explanation of potential performance limitations. It gives you a pretty nice overview but for example, you need spirometry to truly understand respiratory function. You need a moxy monitor to understand oxygen saturation at specific muscles during exercise. You need a whole-sports-science-lab-lotta of kit. And even then, you're still probably reaching due to the potential compensatory mechanisms that keep us in check and balance i.e. are we actually measuring and seeing a genuine limitation, or a compensation?


You see, the more you zoom in, the more you try to measure in isolation, the more you just end up seeing the interconnectedness of the very thing you're trying to measure... and then you just realise the limitation of the measurement. Much like a fractal image, we are just viewing things at a different level of understanding and nuance, but when you zoom out, it's all the same thing, it's the same picture, and likely what you end up doing about it in application shouldn't change all that much. Think about the ball park.


If you have decided to follow the rabbit... These are perhaps some specifics I'm talking about. These all essentially manifest in the same problem, but with different causative mechanisms.


1) Are we seeing a decrement in endurance performance due to the inability to deliver oxygen to the working muscle because of poor diaphragm strength/endurance OR hyperventilation due to poor co-ordination, leading to decreased CO2 at the muscle?


2) Or perhaps insufficient capillarisation at the muscle to extract O2 from haemoglobin?


3) Or maybe we're not getting enough volume of blood to the muscle in the first place?


4) Or perhaps, due to the psychological and physiological drives and requirements to sustain activity (underpinned by homeostatic principles), and the vastness of the potential sites fatigue could occur across the central and peripheral nervous system, it makes it almost pointless to even consider a 'cause'.


Now, imagine the potential variability of looking at this over multiple time points rather than in a singular test? Consider how for example these mechanisms might even change between types of exercise i.e. how swimming differs to cycling, how those differ to running. We could go on and on here. The point is, identifying physiological mechanisms that limit performance is a rabbit hole topic.


There is value in intensity prescription and in understanding more about what happens when performing at specific intensities (speeds/watts). However, it is not going to give you specific and nuanced answers and the golden goose, even if some claim it to do so. If anything, it is in our interpretation of all things considered that holds value and direction moving forward.







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