An Introduction to Applied Bioenergetics & NIRS
How Moxy Monitor is Revolutionizing High Performance Training
To kick off this article on applied bioenergetics and NIRS, i’d like to introduce you to the Moxy Muscle Oxygenation Monitor, which is a device designed to measure both total hemoglobin and muscle oxygen saturation levels in a muscle in live time using near infrared spectroscopy (NIRS). Near infrared light generated by the Moxy sensor travels from the emitter on the underbelly of the device through the skin to interact with the muscle, and then the light is scattered back to the detectors in the sensor.
The sensor takes the raw data and runs it through an algorithm using the Beer Lambert Law, to determine both the total hemoglobin, and myoglobin, in the muscle, as well as the percentage of total hemoglobin that is saturated with oxygen (ie- muscle oxygen saturation, or SmO2 for short). This information is then relayed to, and displayed on, a phone or computer via a bluetooth connection. This is made possible since oxygenated and deoxygenated hemoglobin have different absorbance spectra, or ‘color’ even though that term is more accurately applied to humans perception of visible light.
Near infrared light is able to penetrate biological tissues with less scattering and absorption than visible light and consequently offers advantages for imaging and quantitative measurements
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As a result, NIRS measurements can be used to reflect the balance of oxygen delivery to the working muscles and oxygen consumption in the capillary beds. This makes NIRS a very useful tool for assessing two of the major determinants exercise capacity, which are oxygen delivery and utilization, and since NIRS is a non-invasive technique it makes it very appealing for a wide range of training and competition scenarios.
“The chromophores haemoglobin (Hb) and myoglobin (Mb) are oxygen carriers in blood and skeletal myocytes respectively and their absorbance of near infrared light differs depending on whether they are in an oxygenated or deoxygenated state.” -Jones et al. 2016
“Combining NIRS with simple physiological interventions, such as venous or arterial occlusions,allows quantitative measurements to be made from skeletal muscle. This provides a tool for assessing two major determinants of the capacity of muscles to exercise: O2 delivery and O2 utilization. The non-invasive nature of NIRS makes it an appealing technique for use in adynamic environment and for activities of daily living.”
-Jones et al. 2016
Now that we’ve introduced the concept of NIRS, and the Moxy Monitor, we can move on to discussing bioenergetics, which is the stimulation of metabolic processes that result in energy supply and utilization.
Often times, in discussions about bioenergetics or energy systems, coaches and people will make a hard distinction between two modes of energy production : anaerobic and aerobic.
The former can be broken into the phosphagen and glycolytic pathway, which occur in the absence of oxygen (we’ll discuss why this isn’t truly the case) and the later can be categorized as the oxidative pathway meaning oxygen is needed for its function. This model proposes that aerobic and anaerobic processes occur independent of one another — that is to say, that at any given we are either operating aerobically or anaerobically at a given point in time. The issue is that there are some flaws with this framework.
Many of you are probably familiar with this chart on the left of this block of test— you see it in a lot of coach manuals, textbooks, and courses.
When we look at this model there are some good things about it — for example, it does show that all of the energy systems are working at the same time with different contributions, but past 2 seconds is where it goes off the rails. For example, this model says that from 2–10 seconds we are primarily using phosphagen stores (with a little contribution form the glycolytic and oxidative system), then past 10 seconds all the way upto 2 minutes we’re relying on the glycolytic system, until we eventually transition to solely relying on the oxidative processes to keep us going.
This model is also not in agreement with the contemporary scientific literatue. For example, this model, which we’ll call the conventional view of bioenergetics, says that PCr supplies almost all energy needed for a sustained burst of contraction lasting <10 seconds, after which it is replaced by glycogenolysis.
But, this isn’t supported by the biochemical evidence. In chung et als. paper, Metabolic Fluctuation During A Muscle Contraction Cycle, we see that consumption of PCr is ~40 times greater than values reported by dividing the drop in PCr after minutes of contraction by the number of twitches [which is name possible by newer measurement techniques].
Additionally, in McNully et als. paper, Simultaneous In Vivo Measurements Of HbO2 Saturation and PCr Kinetics After Exercise In Normal Humans, we see that PCr and O2 kinetics are tightly coupled during exercise, and following exercise. This leads to what i’ll typically refer to as the contemporary model of bioenergetics.
In the picture above, we see a visual representation of the contemporary model of bioenergetics. You’ll notice that we still have the phosphagen, glycolytic, and oxidative pathways, but a) they are all overlapping and b) the time frame they are operating in is 0–100 milliseconds. Already we see some major departures from the conventional [classic] model of bioenergetics.
Getting into some of the minutiae of this model, we see that…
1. The support of muscle contraction requires rapid non-oxidative ATP production on the millisecond time scale. So, within 0–15 miliseconds of contraction PCr is broke down to restore ATP. This isnt all that different from that old model except for the fast that it’s occurring on a much faster time scale, but what happens next is where things start to get interesting.
2. In order to sustain contractions we need a non-oxidative energy supply. However, we run into an issue given that glycolytic intermediates [glucose] within a muscle are limited. This is where we need to lean on the biochemical evidence, which shows that glycogen phosphorylase can rapidly increases it’s activity, and as a result glycogen can be broken down to restore the PCr needed to sustain contractions. The question then becomes how we maintain glycogen stores.
3. Between contractions the ATP needed to re-synethesize glycogen, PCr, and re-establish ion gradients comes from the oxidation of lactate. However, only a fraction of the lactate produced needs to be oxidized to restore these energy pools. So, lactate accumulates in muscle cells which is not due to it being a fatigue by-product, but rather it’s due to an inefficiency in this process.
This is all important because it shows us that…
1. Oxygen is always present — therefore, all training is aerobic. In-Vivo oxygen is always a part of energy production, whether direct or indirect.
2. Lactate is always present — therefore, all training is ‘lactic’. This is one that’s kind of confusing to people. Contrary to popular belief, lactate is not a fatigue by product, rather it’s a fuel source.
3. The Oxygen and phosphocreatine (PCr) systems are entangled with exceptions during max strength activities when they may uncouple and have different recovery times. Meaning than when activity begins both oxygen and PCr are utilized rapidly — contrary to the traditional understanding where PCr is utilized first prior to the initiation of oxygen consumption.
4. All energetic processes overlap in time, and the time frame is in milliseconds vs. seconds to minutes — it occurs far faster than classically believed.
5. There are no contradictions with observed Smo2 trends in the contemporary model. However, the classic model is in direct contradiction with what we can observe using NIRS and P-NMR imaging.
Finally, oxygen utilization responds immediately to load. There is no ‘anaerobic’ system — when muscle oxygen saturation reaches 0% performance stalls. Period.
Knowing what we know now, a natural set of question begin to arise when we start to put pen to paper and write energy system training sessions for our atheltes. “If all training is aerobic, and all training is lactic, how the heck can we do a-lactic anaerobic training?” Great question my friend. The simple answer is that don't, or rather we can’t.
When people perform ‘a-lactic’ power training they assume lactate isn’t generated because it doesn’t show up on test results. Does this actually mean there was no lactate generation, or that it was being consumed for fuel? When you take a lactate sample from the ear or finger there is a time lag since the sample isn’t taken at the source of the working muscle.
In reality the measured lactate level = (lactate production)-(lactate consumption). The reading on a lactate analyzer tells us the difference between how quickly lactate is being produced and consumed, not whether it is being produced in the first place. In actuality lactate production is incredibly high during ‘a-lactic’ training intervals, but it’s being consumed an incredibly fast rate.
All Training is aerobic, and all training is lactic. When we can speak in these terms and ditch a lot of the classic ideas about energetics we can come new conclusions that are better informed.
For example, lets take maximal effort sprint performance. Traditionally, this type of work would be classified as a test of ‘a-lactic’ power or endurance. For example, in the picture to the left we have a chart from a popular energy system training course that says, “As a rule of thumb, the closer the events duration is to one minute, the lower the aerobic contribution to overall performance will be. The opposite is also true: the longer the duration is, the more dominant the aerobic system will be.” Oh really? That’s odd given that oxygen is utilizing immediately upon load, even during a 30 second max effort sprint, and that muscle oxygen saturation begins to recover as soon as the sprint ends, as seen in the picture below.
When we think in these confined terms and categories, like ‘alactic-anaerobic’ or ‘lactic power’, it leads us to natural conclusions as to how we get better at certain types of events. But, when we can look past these outdated models of bioenergetics we can approach training through a new lens. Knowing that oxygen is utilized immediately upon the start of activity, we can think in terms of ‘limiting factors’ in oxygen delivery and consumption rather than what ‘energy systems’ are limiting us. So, rather than saying “my athlete needs to get faster on a 200m sprint so we need to improve her lactic power” we can identify the individuals rate limiting factor, whether that’s the rate of oxygen utilization or the ability to supply oxygen to the working muscle.
If you’re interested in learning more about the concepts discussed in this article feel free to reach out to me at “Evanpeikon@gmail.com”. I offer consulting, and additional services for coaches, sports teams and organizations, which you can learn more about here. Additionally, if you’re interested in learning how to identify and train limitations on your own, i’ve partnered with Moxy Monitor to produce an NSCA CEU approved courses called the Science & Practice of Performance Enhancement with NIRS, which you can find here. This course is packed with information and practical takeaways for athletes and coaches, whether or not they use a NIRS device.
Also be sure to check out some of my other articles like….
Performance Physiology 101: Identifying and Training Respiratory Limitations
An Integrative Approach to Load Management & Return to Play
Why Does My Lower Back Always Blow Up During Metcons? An Applied Sports Science Approach
