Understanding an Athlete’s Physiology

Building an optimal training program for an endurance athlete requires a deep understanding of the athlete, and their potential capability. And while the results of race day aren’t always controllable, there are ways of optimizing the efficiency of training to maximize the performance potential of each individual you work with. 

The key: understanding the athlete on a physiological level!

Three pillars of physiological training optimization

Understanding an athlete’s physiology allows for the optimization of training for that individual. And optimizing training for an individual has three major components: physiological assessment, training readiness, and real-time adjustment of intensity. 

Assessment

Physiological assessment tells you what kind of athlete you are training. Are they extremely efficient with a small engine that can go all day, like a Prius, or do they have a massive engine, that is less efficient but can output very high power like a Corvette. 

Physiological assessment can also tell you how an athlete is adapting to training. Do they respond better to higher intensity work or do they respond to increased training volume. 

Finally, assessment can give you a road map to what is limiting an athletes performance physiologically. Is the athlete capable of delivering enough oxygen to their muscles, can their muscles use the oxygen that is being delivered, or maybe they aren’t able to exchange oxygen and carbon dioxide adequately with the environment.

Understanding the physiology of your athlete, how their training is affecting their physiology, and what is limiting their performance will give you tools to optimize an athlete's training plan.

Training Readiness

Assessing an athlete’s physiology is just the first step to optimizing a training plan. 

All good coaches are aware that training stress and the ability to absorb training  stress is an important factor for making continued progress. However, there are very few tools that are sensitive enough to allow for the evaluation of training readiness after a short bout of exercise, like after a warm-up. But barring any sickness, a warm-up is a perfect time to evaluate if an athlete’s physiology is ready for the work that is programmed.

For example, if an athlete repeats a similar warm-up each day, then depending on how that warm-up goes and if you have the right technology, you should be able to determine if the athlete should train as planned or adjust training because they are too fatigued. 

This is a common problem among athletes. 

How does an athlete know if they should train normally, or defer their workout to the next day? 

And while technology like heart rate variability is a step in the right direction, it is a resting measure and only one piece in a larger puzzle. A dynamic measure of training readiness that evaluates how the athlete responds to exercise (a warm-up) provides more direct information and gives athletes more confidence to make adjustments when necessary. 

Real-Time Training Intensity Adjustment

Performance measures like first threshold and FTP can change during a prolonged workout, and in response to accumulated stress, like long training blocks.

So why don’t coaches and athletes adjust their training intensity in response? 

The answer probably has to do with the fact that most technology, like heart rate isn’t sensitive enough to capture these changes for us to make confident changes in response to varying stress and fitness level. 

Yet, adjustment of training intensities on a given day could represent a more time effective way to train that would lead to more optimal adaptations and reduce the risk of set backs like sickness, and injury. 

The overarching goal of any training plan is to make an athlete better, i.e. improve their performance. 

The combination of physiological assessment, integration of physiological parameters into the training plan, evaluation of training readiness, and real-time intensity adjustment; based on how an individual is feeling and how their physiology is responding daily are keys to optimizing an athletes ability to perform on race day.

Using Moxy (NIRS) for Training Optimization

The only technology that can be used for the 3 pillars of training optimization mentioned above is near-infrared spectroscopy or NIRS.  NIRS devices non-invasively measure muscle oxygenation (SmO2) in real-time while you exercise.  Moxy Monitor is the only NIRS device in the world that can isolate the signal to the muscle layer and has been shown to measure accurately on a scale of 0% to 100%.  

But how can you use your Moxy Monitor to optimize assessment, evaluate training readiness, and make real-time training intensity adjustments? 

This blog post will provide an overview of how to do that. Subsequent posts will detail step-by-step how to achieve optimal training with Moxy. 

Assessment with Moxy Monitor

Graded Exercise Tests

As outlined earlier, assessing an athlete’s physiology is the first step to understanding what intensities of training will be appropriate for that athlete. 

Typical assessments involve completing a continuous ramp or step test, or some iteration of these tests but with rest in-between each step, with exercise intensities gradually increasing from low to high, termed a graded exercise test. 

The goal is to see how an athlete responds to various exercise intensities. From these assessments you can determine physiological markers that are indicative of performance (i.e. economy, thresholds, and maximal aerobic capacity). 

You can also identify thresholds to gain an understanding of where an athlete’s physiology shifts/changes (first and second threshold) to facilitate the intensity of exercise that is being completed (i.e. build individualized training zones). 

Thresholds represent exercise intensities where the body changes how it responds to the stress of exercise. Generally, these thresholds represent points where the body starts to shift/favor different modalities of energy production. For example, first threshold represents the first major shift away from fat oxidation towards higher carbohydrate oxidation, and the second threshold represents a shift from primarily using oxygen as a source of energy production to increased reliance on energy production from non-aerobic sources. Thresholds are useful because the rate at which the body accumulates training stress (i.e. Fatigue) increases exponentially s we move from under first threshold, to between first and second threshold and finally above second threshold.

Previously, this type of testing had to be done in a lab with equipment that costs thousands of dollars. But the Moxy allows for lab grade physiological evaluation in the comfort of your home or even outdoors (if you can control the exercise intensity well enough). 

Because the Moxy measures oxygen delivery and consumption at the working muscle it’s highly sensitive to changes in muscle oxygen physiology. Breakpoints in skeletal muscle oxygenation (SmO2) measured with Moxy, have been shown to be highly correlated with first and second lactate and ventilatory thresholds (Batterson et al. 2023, Feldmann et al. 2022). 

Thus, by placing a Moxy monitor on a working muscle and having an athlete complete a graded exercise test, then finding inflection or breakpoints in the SmO2 data, you can determine an athlete’s thresholds which can be used to determine their training zones.  

Interestingly, thresholds are not fixed parameters. They change daily in response to previous training stress, temperature, altitude, nutrition, other life stresses, and many other factors. This is why it is important to be able to adjust your training intensity based on the daily training conditions. By learning what these responses look like, the athlete can make training load adjustments in real-time. This is detailed further below.

Limiter Assessment

Another, unique aspect of continuously measuring SmO2 with the Moxy is that you can measure both exercise oxygen kinetics AND oxygen recovery kinetics. 

By adding rest periods between each stage of a graded exercise step test we can start to understand what is LIMITING an athletes oxygen delivery and utilization. By identifying an athletes limiter we can specifically address that limitation by modifying certain aspects of training. 

To do this, you would have an athlete complete a step test, but with 1-minute breaks in between. Then based on the SmO2 changes during exercise and during rest we can figure out their limiter. If this sounds nebulous don’t worry we will go into greater detail in upcoming posts and you can read more about it in the Moxy Training Integration Guide.

How to Determine Training Readiness with Moxy Monitor

A key aspect of training that many athletes aren’t paying enough attention to is a proper warm-up. 

A proper warm-up is key to preparing the body for the upcoming work of training and racing as well as properly absorbing the work that is being done. The addition of tracking SmO2 will help to optimize your warm-up and give indications of training readiness, here’s how. 

Warm-up

There are two phases to an optimal SmO2 warm-up: the cardiovascular preparation phase and the muscle preparation phase. 

GOAL: to increase SmO2 as high as possible without inducing fatigue. 

The cardiovascular preparation phase involves low intensity activity completed in a step-wise fashion. I like to start with 75% of first threshold for 5 minutes and increase to 85% of first threshold for another 5 minutes. 

What I am looking for in this phase is that heart rate increases, and SmO2 initially decreases then gradually rises. IF SmO2 goes down and stays flat, then you may be going too hard for SmO2 to increase. In this case, I suggest reducing intensity during the following days warm-up to see if you can elicit an increase in SmO2. This increase in SmO2 indicates that the cardiovascular system is delivering more oxygen than the muscle needs, essentially we are priming the pump to deliver enough oxygen when we start the next phase.

The next phase is muscular preparation. This involves accelerations, or repeat desaturation. Where we accelerate or increase power output to a point where SmO2 decreases. There are two acute phases to SmO2 decreasing, a rapid phase where SmO2 falls rather quickly, then a slow phase where SmO2 begins to plateau. During your acceleration, it’s time to stop when SmO2 starts to plateau! 

If you’re watching SmO2 it will look something like this 65%, 60%, 50%, 40%, 35%, 30%, 28%, 27%, 26%. When SmO2 stops decreasing as rapidly this is when you stop. And by stop I mean COMPLETELY slow down and stop. Rest with your leg in the same position and wait until SmO2 reaches a peak. 

Then repeat the acceleration, but a little bit harder. When you reach the beginning of a plateau STOP again, and wait until SmO2 reaches another high. Repeat this process until SmO2 reaches the same high twice in a row. 

Training Readiness

Because SmO2 gives us indications of how well warmed up we are, tracking the highest SmO2 and lowest SmO2 as well as the dynamic range of SmO2 during a warm-up and over time will allow us to track training readiness. 

Following a standardized warm-up (determined loosely above, and in greater detail in subsequent posts) determine the highest SmO2 and lowest SmO2 and the difference between the two. 

Compare this number to previous days numbers. 

IF the dynamic range is lower then consider how you feel and consider taking an easier day that day. 

IF the dynamic range is the same train as normal.

IF the dynamic range is higher then consider doing a harder day that day OR train as normal.

How to Adjust Training Intensity in Real-time with Moxy Monitor

A proper warm-up and determination of training readiness gives us an idea of HOW we can train on a given day but we also need to consider our bodies ability to output mechanical force (power or speed) and how that changes on a daily basis. 

Sometimes we may feel really good but for some reason we just don’t have our “normal power output”, other days we feel good and this correlates with much higher force generation ability. The point, is that mechanical output can be HIGHLY variable day to day, so using SmO2 can help us to adjust our force output in response to what our physiology is telling us. But we can't just rely on an SmO2 number. We have to watch what is happening to SmO2 at a given steady load (i.e. SmO2 response).  

SmO2 Response to Training 

SmO2 response or how SmO2 is changing in response to a given steady load (power or speed) tells us the balance between cardiovascular oxygen delivery and muscular oxygen utilization which gives us an indication of what zone we are in. 

IF SmO2 is increasing then we are most likely exercising under our first threshold. 

IF SmO2 decreasing then remains flat we are exercising between first and second threshold. 

IF SmO2 continuously decreases given a steady load we are operating ABOVE second threshold.

Here's how you can use this for specific workouts.

Zone 2 Training 

Generally, at exercise intensities BELOW first threshold SmO2 will increase OR remain high with little noticeable change upon added load. The first exercise intensity where SmO2 bumps down or goes from increasing to flat is where your first threshold occurs (i.e. Fatmax, VT1, LT1, NIRS BP1). This is highly correlated with the upper boundary or “Zone 2”. So if you want to truly dial in your zone 2 training each session you would follow this approach by figuring out where SmO2 goes from increasing to flat OR where SmO2 goes from some baseline level to a lower steady SmO2. 

Threshold Training

At exercise intensities below second threshold SmO2 will decrease (initially) then remain steady. IF you exercise ABOVE second threshold SmO2 will continually decrease OR if you add more load SmO2 will bottom out and stay the same (if you are measuring in a non-limiting muscle we will talk about this later). 

For threshold work you want to find the exercise intensity where SmO2 transitions from being able to establish steady state to SmO2 continually decreasing OR the first exercise intensity where SmO2 levels off and doesn't go lower with more exercise intensity. 

After you have found this point, complete your threshold workout as you normally would. 

Interval Training

At exercise intensities above second threshold SmO2 will decrease until it reaches a low point. The rate at which SmO2 decreases is directly related to the exercise intensity that you are working at. The higher the intensity the faster you will reach your lowest SmO2. 

For intervals, you can pace yourself to reach your lowest SmO2 in a certain time period, OR you can stop your interval when you reach your lowest point. 

Then you can rest for a fixed amount of time or following how your SmO2 is responding. 

There are a lot of different ways you can modify interval training in response to SmO2 which we will go over in more detail in upcoming posts. The bottom line: you can use SmO2 to modify your easy, moderate, and high intensity work for more optimal exercise response.

Conclusion

Monitoring muscle oxygen with Moxy represents a way of optimizing an athlete's training. Start with evaluating an athlete’s physiology with an assessment, then evaluate training readiness with a warm-up each day, and within each training session modify the exercise intensity for the expected physiological response.

All of this will allow for more efficient training, potentially saving time and optimizing an athletes physiological response to said training. Ultimately, a coach’s job is to help an athlete perform better. And understanding the principles of training and racing with Moxy is a way of doing just that.

The series of upcoming posts will aim to detail all aspects of creating optimal training and racing with Moxy.