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Introduction into Bioenergetics via Muscle Oxygen Saturation

Performance Training Personal Training

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At the tail end of 2018, we introduced a new piece of technology into performance clients programming, specifically those involved in cyclical sport participation (Rowing, Cycling, Running etc.). Our intention was dual purpose, not only to drive client training and performance, but also provide a greater insight into the newer models of bioenergetics, the study of the transformation of energy in living organisms.

This technology is a Muscle Oxygen Monitoring (MOXY). As the name suggests, this sensor provides continuous monitoring of oxygen saturation within the muscles of participating individuals. For those that have seen the kit in use, or had it involved within sessions, this small device uses Near-Infrared Spectroscopy (NIRS). A sensor that emits a light that is at, and just beyond, the red end of the visible light spectrum, something the human eye barely detects.

The sensor is placed on the working muscle of an individual, with the light shone into the muscle through the layers of skin and fat. When inside the muscle, the light itself isn’t fully absorbed, but rather scattered through the tissue. This means the residual light can be picked back up by the sensor. With this is mind, the near-infrared light that is absorbed reacts differently to haemoglobin and myoglobin molecules that have oxygen bound to them, as opposed to those that don’t. From this, the percentage of molecules bound to oxygen can be monitored by taking optical measurements at different wavelengths. For example if we have a 30 molecules of which 15 are saturated with 02, this would be a value of 50% saturation.

So in simple terms, MOXY is a tool for measuring Haemoglobin and Myoglobin oxygen saturation in the capillaries of the muscle.

We also benefit from a second measure through this training tool, we can establish not only those molecules bound to oxygen vs those unbound, but also the total amount of haemoglobin and myoglobin (30 in our above example). Whilst a relative measure with arbitrary units, by determining if the amount is either increasing, decreasing or remaining stable, we can make the assumption of ongoing blood volume changes within the muscle. 

During high intensity movements and high loads, the muscle is reliant upon the initial usage, and subsequent creation, of the energy molecule adenosine triphosphate (ATP). This molecule is resynthesized through the chemical phosphocreatine (PCr), maintaining a balance of energy supply vs demand. The replenishment of this energy system is primarily based on aerobic methods, oxygen therefore needs to be present. Oxygen and phosphocreatine are tightly bound together in depletion and repletion rates within most forms of exercise.

As we will discover over the next few insights, muscle oxygenation responds almost instantaneously to to exercise. Whilst the stored supplies of ATP will very unlikely never fall below approximately 40% within the body, the supply of phosphocreatine can be more severely depleted. Without 02 providing the replenishment of these systems, ATP cannot be produced, without ATP, fatigue ensures and muscles no longer have the capacity to contract.

By measuring muscle oxygen saturation we therefore have a proxy measure in real-time of the demand and supply within a muscle. The ability of the respiratory and cardiac systems to supply oxygen, and the mechanisms within the muscle for 02 consumption, all become determining factors in the fatigue level and recovery effort during exercise itself. 

The goal of this insight is to provide some visual examples of simply the first of our two measures gained from MOXY, muscle oxygen saturation. This value is represented as a percentage from 0-100 and will be abbreviated as Sm02. For introductory purposes, we can assume that these measures are representative of any major working muscle in an activity, a quadricep in a Squat or a pectoral muscle in a Bench Press for example.

In the first graph below, we have a basic reading for Sm02 (these graphs have been data smoothed and transported into Excel to provide a clearer reading). Our vertical axis representing Sm02 from 0-100%. 100% being complete saturation of bounded haemoglobin to oxygen, and 0% representing zero bounded haemoglobin to oxygen. 

At the onset of activity, we see a sharp decrease in the saturation of 02.

  • As a brief caveat for anyone who has been through an introduction to sport science or physiology, we’re taught that we have 4 energy systems, an ATP, PCr, Glycolytic and Aerobic, with energy not involving oxygen until the durations reach over 2-3mins. Unfortunately the models still being taught through schools, colleges, universities and the vast majority of courses and qualifications are vastly outdated. Research into bioenergetics has moved a long way, unfortunately it takes time for information to trickle down. For more information, take a look at the Glycogen Shunt Model of bioenergetics.

Returning to our graph, at exercise onset, 02 desaturates within the muscle. ATP is being used rapidly and phosphocreatine is primarily responsible for replenishing ATP supplies via aerobic means to meet the demand in place. At cessation of exercise, we see an increase in Sm02 as the body reloads its stores of phosphocreatine. In the example above, we have this action repeating for 4 sets. Energy demand winning over supply during exercise, whilst supply rebounds to replenish stores during rest periods. 

When it comes to exercise, whether it’s intervals on a rower, shuttle runs, sets and repetitions of a resistance training lift, we are aiming to manipulate the demands and supply of energy. We want to perform an activity, recover and repeat. How we manipulate these variables will have direct outcome on the internal environment we can create within the muscle with regards of Sm02.

In an inactive individual at rest prior to activity, we can place a MOXY sensor onto a soon-to-be working muscle, and examine both Sm02 and blood flow. Both these figures will remain relatively low and stable at rest. However with little demand for either 02 or increased blood flow, these figures can be manipulated by increasing activity, a prime example of this is via a “Warm-Up”.

We will look at this more specifically in a future insight, however the aim of a warm up from a bioenergetic standpoint is to increase blood flow into target muscles and increase energy substrate availability. If we look at our two basic measurables via MOXY, we have percentage of 02 saturation and total blood volume. We can use MOXY as a tool in determining the effectiveness of this part of a session. Our goal here is to increase 02 saturation and blood volume, preparing the individual for the movement pattern and load at hand thus improving physiological function. 

If our session is lower body specific for example, we’re aiming to drive blood flow into the lower extremities through the warm up and provide a stimulus that will overall increase 02 saturation levels. Our end result being that from a resting Sm02 we may have a purely hypothetical value of 50% Sm02, at the end of an effective warm-up we may have a figure closer of 80-85% Sm02. 

This figure can now be used within our training, this represents our recovery baseline. 

If we take a Squat workout for example, using a 4×8 protocol typically assigned for strength work, in traditional models we may apply a load, number of reps expected at that load and a number of times we should repeat the set and a rest time between these sets. However these are figures that are an accumulation of research averages, it has no capacity for allowance of individual physiology. How do we know the weight was a sufficient stimulus, the reps creating enough volume, or that we used the appropriate recovery time?

Whilst these models provide a basic understanding of how to approach programming, they’re unfortunately outdated and still treat individuals as linear equations of input = output. Unfortunately this isn’t always the case. If our aim is to be surgical in how we approach training, removing unnecessary reps, sets and exercises and utilising only that which moves an individual forward from a performance goal, this is a critical consideration.

Using MOXY we can now use real-time 02 saturation at the muscle to determine rest using our recovery baseline as our indicator. We squat, driving Sm02 down for 10 reps, we rest until we return to recovery baseline and go again. In this scenario we can assume that our proxy for phosphocreatine, Sm02, has recovered. Far less subjective, far more driven by internal physiology.

We can therefore make an educated assumption that we have an internal physiological environment in which the individual can squat again with appropriate load and create the same desired adaptation.

Using the same graphic again, we can use MOXY to determine the type of environment we’re trying to create and the resulting outcome we desire. With our recovery baseline in place, we can also create a performance baseline for activity. Using our 4×8 protocol, we could use a fixed figure such as %1RM in this case let’s use 80% of a 100kg 1RM, 80kg for simplicity, with MOXY in tow, our opening set now becomes an establisher of our performance baseline. How low can we drive muscle oxygen saturation…

This is of course a subjective component and requires exertion of maximal effort for a given goal.

Can we drive Sm02 down within the target rep range?

Is the load enough to actually cause the desired stimulus within the muscle and desaturate fully?

We now however have two metrics we can use for our 4×8 protocol, can we desaturate to the performance baseline, and can we allow sufficient recover to re-saturate back up to the recovery baseline. We’ve taken away the arbitrary usage of time-based recovery, this is now physiology driven. 

There are a huge number of extenuating factors, alternate variables and further detail that goes into this type of programming however for the purpose of our introduction this is a vital concept.

Depending on the goal of our session, whether its strength, hypertrophy or some form of conditioning, how we manipulate the variables of 02 will have a massive impact on the type of physiological change we see in an individual. 

In the example below we have a hypertrophy protocol aiming to creating hypoxia and metabolic stress within the working muscle without any significant Sm02 recovery, one of the key components of stimulating hypertrophy. We could achieve this via a maximal effort to quickly drive Sm02 down, before performing a reduced load movement of the same pattern to maintain low Sm02 until exhaustion (i.e. Dropsets).

In the following example we could take a scheme of 3×5 on a maximal strength exercise, our goal being to drive mechanical tension and fibre recruitment under high loads. In this case we can apply an enhanced recovery protocol in which we drive Sm02 down during exercise with the aim to recover ABOVE the recovery baseline established during the warm up. This ensures the individual is maximally recovered for the following set.

Our final example below, is that of incomplete recovery. In which we drive Sm02 down to the performance baseline, and instead of recovery back or beyond baseline, we reach approximately 50% of this figure before going again. We may utilise this strategy when aiming to improve strength endurance potentially via a series of sets such as 2x 3×30/30 in which we work for 30sec, rest for 30, for 3 rounds. Take rest back to recovery baseline and go again.

When we consider exercise at its simplest form, we’re fighting a battle of energy supply vs energy demand. How successfully we do this involves a chessboard of moving pieces that is unique to each and every individual. MOXY allows us to take a look into what is happening at the level of internal physiology. It changes how we think about bioenergetics, physiology and exercise as a whole. 

Over the next few weeks we’ll dive into not only our second measure via MOXY, total haemoglobin and how we can interpret blood flow trends such as vasodilation, vasoconstriction, venous and arterial occlusions. As well as looking at how we can utilise tools such as MOXY for use within strength training and conditioning. 

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