If you are not familiar with Near Infrared Spectrometry (NIRS), it allows you to see real-time muscle oxygenation (SmO2) and hemoglobin index (tHb). What this means is that we can see the rate of oxygen delivery and removal from a muscle group or area real time.
Hemoglobin and myoglobin are capable of releasing oxygen at a local muscular level. What NIRS does is assess how much oxygen is present based on hemoglobin and myoglobin is available. What NIRS essentially breaks down is the balance between oxygen supply and demand at a local level.
If more oxygen is being demanded than is being delivered, as indicated by lower dissolved oxygen levels in the tissue, the oxygen saturation will go down (1).
An important distinction for NIRS, relative to a pulsometer, is that it assesses oxygen utilization relative to hemoglobin concentration. Hemoglobin/myoglobin release oxygen at a local level (capillaries). Hemoglobin do not release oxygen within arteries, so hemoglobin content is not a reliable indicator of oxygen saturation or desaturation rates.
This is what brings us to Evan’s book. If anyone has performed an exercise stress test, you know that the mode has a huge impact on performance. For instance, a bike test is a lot different than a graded treadmill test. The concentrated fatigue versus a more global fatigue is drastically different. This is where NIRS comes into play, to assess the localized differences.
The book is a deep dive into issues with exercise prescription and its flaws based on incomplete understanding of bioenergetic models. For instance, Evan has a very compelling argument against the traditional Energy System Model of Phosophagen, Glycolytic, and Oxidative. What is obvious with NIRS is that oxygen and even lactate are present at all times regardless of the activity. To even further the point, more heavily developed anaerobic athletes utilize oxygen more so early during phosphagen activity than more aerobically developed athletes. If this model is the foundation of bioenergetic prescription, we will assuredly have some output problems.
For me, this is akin to other models that challenge accepted models of thinking. For instance two dimensional anatomy and physiology does not apply as completely as fascial lines and hydrodynamics to three dimensional movement. To a point, you will have to ‘unlearn’ everything you know.
The more important aspect is that you will have to be more polished with foundational sciences such as physics or chemistry. If you do not know universal laws, you will struggle with models that need updating. Gravity will, to some extent, always exist. We can take solace in learning hydrodynamics that internal environments operate differently than external environments as well as knowing that we are all being pulled towards earth regardless of the action. The same note is that we are all creating ATP through ATP-PCR, glycolysis, Citric Acid Cycle, and Electron Transport Chain. Energy is not created nor destroyed, it just transfers from one place to another. Once we know that, we do not have to marry ourselves to any model. We use the one that takes the most current and accurate depiction of what is happening.
If we can understand the rates of oxygen delivery and subsequent removal, we can understand a ton more about how the system functions bioenergetically. If we use more oxygen, demand is more. This will result in faster rate of glycolysis and an increased rate of lactate dehydrogenase converting pyruvate to lactate over acetyl CoA. If power is the goal, we can see how and why we are fatiguing faster and more accurately. We can prescribe more directly based on that logic than if we did not.
Evan’s got really good insight off mixed versus single focus training. This is an important notion to talk about because all sessions with acyclical athletes are going to be mixed to a degree. Mixed focus of power, strength, and capacity are all at play during training. Having something that analyzes the rate of oxygen saturation and desaturation levels shows the impact of a certain focus or order of that focus.
Evan did a really good job on this book, I highly recommend it. Take time to sit and think about all models that you may use and how and why they might be incomplete or possibly incompatible with how we do things now.
- Introduction to Muscle Oxygen Monitoring with Moxy