Using Biomarker Measurements For Real-Time Pace Guidance
Using Real-Time Data To Guide Pacing For Endurance Sports
In today’s newsletter you’ll learn how to use real-time physiological data to guide your pacing in order to minimize fatigue and maximize performance during training and racing.
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Using Real-Time Data To Guide Pacing
Traditionally systemic physiological responses such as changes in VO2, heart rate, and blood lactate have been used to quantify exercise intensity and inform athlete’s pacing strategies during training and racing. An alternative approach is to use local indicators of a working muscle’s status, such as muscle oxygenation (SmO2), nitric oxide (NO), and oxygen consumption (mVO2), which can be monitored with a NNOXX wearable device in real-time.
NNOXX’s non-invasive biomarker measurements provide a simple, safe, and reliable way to determine exercise intensity based on changes on the metabolic status of working muscles, which are associated with systemic changes in whole-body metabolism. As a result, athlete’s can use their NNOXX data to adjust their pacing and exertion during training and racing to maximize performance.
In a study, titled Near-Infrared Spectroscopy: More Accurate Than Heart Rate for Monitoring Intensity in Running in Hilly Terrain, scientists found that while heart rate was unaffected by continuous changes in terrain and intensity during exercise, muscle oxygenation (SmO₂) reflected these changes and strongly correlated with changes in oxygen consumption.
“Recently used exclusively for scientific purpose, this NIRS based variable may offer a more accurate alternative to HR to monitor running intensity in the future, especially for training and competition in hilly terrain.” -Born et al., 2017
These findings suggest that SmO₂ may offer a more accurate alternative to HR for monitoring exercise intensity, particularly over mixed terrain.
Where Do I Put My NNOXX Device?
To guide pacing during endurance exercise, the NNOXX wearable should be worn on the primary locomotor muscle. For activities such as cycling, rowing, or running, the vastus lateralis (outer quadricep, as demonstrated below) is the most reliable measurement location.
However, it should be understood that there is a heterogeneity of responses across different muscle sites. As a result, if you were to put a NNOXX device on two different muscles you would see two different responses to exercise. This is of little concern for the majority of activities, but becomes increasingly relevant during full-body endurance sports such as Crossfit, where the primary locomotor muscle can change over the course of a workout. Due to the individualized nature of such events, this guide will focus solely on cyclic activities such as cycling and running.
Real-Time Pace Guidance— The Basics
Muscle oxygenation reflects the balance of oxygen supply and demand in the working muscles. Thus, if SmO2 is going up oxygen supply is greater than oxygen utilization and vice versa, as demonstrated in the image below. Furthermore, if SmO2 is unchanging it means oxygen supply and demand are equal, and a steady-state has been reached.
At the start of exercise, muscle oxygenation (SmO2) will rapidly decrease from its baseline level, and the higher intensity of the exercise, the greater the rate and magnitude that SmO2 will decrease. If an athlete can reach a metabolic steady state, SmO2 will eventually level off and stabilize. The higher the exercise intensity, the lower the stable SmO2 value. Finally, when an athlete stops exercising, SmO2 will increase, and the fitter that individual is, the faster SmO2 increases during rest.
For example, my resting muscle oxygenation level in the image above is ~65%. When I begin running at a 7:30/mile pace, my SmO2 rapidly declines but eventually levels off at ~45%, indicating that I've reached a steady state output. If I were to run slightly faster, my SmO2 would decline further before leveling off at a lower level. If I suddenly began to sprint, my SmO2 would decline until it reached a nadir, at which point I could no longer sustain my output. Then, once I rest, my SmO2 rises, eventually reaching my baseline resting level.
Each individual will have a different minimum and maximum SmO2 value. These values can be learned from experience. For example, my resting SmO2 values range from 60-70%, and my minimum SmO2 value during maximal effort exercise is 20-30%, as demonstrated in the image below. Thus, the dynamic range in my SmO2 signal ranges from 20-70%. Within that range, there are SmO2 values that correspond to different exertion levels.
With trial and error, each individual can determine their minimum and maximum SmO2 values and how they change based on how well-rested and recovered they are. Additionally, each individual can learn to identify what ranges of values are easy or challenging to maintain, which can be used as a real-time feedback tool to guide exercise intensity.
Once an individual intuitively understands how varying SmO2 levels relate to their level of effort, exertion, and fatigue, they can associate different bodily sensations with their SmO2 level. For example, I've found that when my SmO2 level gets below ~55%, my breathing starts to elevate ever so slightly. However, I can still hold a full conversation and sustain this SmO2 level indefinitely without feeling like I'm exerting myself. Additionally, I commonly perform long-duration (>2 hours) cycling workouts in the 50-60% SmO2 range.
When my SmO2 level is between ~40-50%, my breathing starts to elevate, and I begin to feel a mild burning sensation in my muscles. This level of exertion is comfortably challenging, and I can maintain this SmO2 level for an extended duration. However, once my SmO2 is 30-40%, my breathing becomes labored, and my muscles have an uncomfortable continuous burning sensation. This level of exertion is unsustainable, and I have limited time I can spend in this intensity range before fatigue starts mounting.
Finally, if I push below 30% SmO2, I can no longer coordinate my breathing, and my muscles rapidly fatigue. Often, I'll see my SmO2 level in this range if I'm aggressively climbing a hill on my bike. Knowing that I have limited time I can spend at this oxygenation level, I'll use it as a sign that I need to reduce my power or speed to avoid 'spilling over' to the degree that I cannot recover.
Try it yourself!
Place your NNOXX device on your outer quadriceps muscle and record data using the unguided workout mode in NNOXX's mobile app. Now, begin running, biking, or rowing at a low intensity, observing your muscle oxygenation (SmO2) values.
After a few minutes, increase your intensity to a moderate exertion level, and observe how your SmO2 value changes. Once your SmO2 has stabilized, you can try exercising at a hard exertion level or even try to do a 20-30 second sprint. How low did your SmO2 level get? After you've rested and recovered, how high did it get back up to?
With experience, NNOXX users can learn what SmO2 values correspond to their easy, moderate, hard, and maximal effort intensity zones.
Real-Time Pace Guidance— Intermediate Level
To make the most of monitoring muscle oxygenation (SmO2) for real-time pace guidance, it’s important to also monitor your power or speed as well, which can be done with a power meter, smart watch, or a GPS-enabled mobile phone. Under normal circumstances muscle oxygen and external load are negatively correlated, which means that as power increases, muscle oxygenation decreases and vice versa. The image below summarizes the expected relationships between muscle oxygenation (SmO2) and external load.
However, there are circumstances where the above relationships do not hold, and in these cases the observed data trends provide important clues about an athlete's internal physiologic state. For example, there are instances where an athlete is holding a stable power output and SmO2 level (i.e., a steady-state), but then suddenly their SmO2 level begins to climb upwards. This is an indicator that the athlete is changing their muscle recruitment pattern, which could be intentional or unintentional. For example, let’s say I'm biking at 300 watts and an SmO2 level of 40% and my outer quadriceps are starting to feel fatigued. I may decide to use my hamstrings to pull on the pedals more, which will reduce the load on my quadriceps muscles, resulting in a slight increase in their SmO2 level.
There are also cases where an athlete is holding a stable power output and SmO2 level (i.e., a steady-state), but then suddenly their SmO2 level begins to gradually decrease This means that the athlete’s muscles are having to work harder to maintain their power output, and is an indicator of increased fatigue and decreased proximity to failure. For example, let’s say I’m biking at 300 watts and 35% muscle oxygenation, but after forty minutes my respiratory muscles start to fatigue and I can no longer supply oxygen to my working muscles at as fast a rate. In this case, my oxygen consumption in the working muscles would begin to supersede my oxygen supply, resulting in a progressive SmO2 level as I fatigue.
As previously stated in the section titled, Real-Time Pace Guidance— The Basics (Beginner Level), it’s important to build awareness around your own normal muscle oxygenation and power output levels. For example, you should know your minimum and maximum SmO2 levels, as well as your normal SmO2 ranges during easy, moderate, and hard exercise intensity bouts. You should also have an understanding on your maximal power output level in your selected exercise modality, as well as your critical power, which is the highest power output you can sustain before exhausting your finite energy supply. With this information, you can begin to build awareness around the relationship between your power output and muscle oxygenation levels, and these relationships change over time as you get fitter (i.e., being able to hold a higher power output at a given muscle oxygenation value) or how they change within a workout as you fatigue (i.e., needing to lower your power to stay within a certain range of SmO2 values).
Through trial and error, you can learn to manipulate your muscle oxygenation level during exercise by altering your power/pace, cadence, breathing volume and frequency, and body position. For example, suppose you're cycling and are approaching your minimum SmO2 value. In that case, you can lower your power output to prevent your SmO2 from bottoming out. Alternatively, say you're in a race, and a competitor passes you. You may notice that your SmO2 value is relatively high, meaning you have sufficient energy reserves to increase your power output.
In another instance, you may be on a long bike ride as part of your training, holding a submaximal power output and aiming to keep your muscle oxygenation level in a moderate intensity range. In this case, you could adjust your gears and cycling cadence to see if you could increase your SmO2 without changing your power. If so, you've improved your movement efficiency.
You can even work on manipulating your movement cadence, breathing volume and frequency, and body posture to increase your pace at a given SmO2 level. For example, I'm running one-mile repeats with my SmO2 at 35-45%. From set to set, I could try running with a different cadence, increasing my breathing frequency while maintaining my volume, or altering the position of my torso to see if I can increase my speed without my SmO2 level going below my target range.
Try it yourself!
Below is a sample workout for cyclists, designed to help them understand how their cadence, breathing, and body position impact their muscle oxygenation readings.
10:00 Wattbike at 90-100% FTP, Rest to recovery x2-4 Sets
*Start with what feels like normal relaxed breathing for this effort. If you feel like you’re not getting enough air in, aim to increase your respiratory rate (RR) while maintaining the depth of your inhale and exhale. Try shifting your gears and cadence as you get comfortable with this power output. Can you increase your muscle oxygenation while keeping your power stable? If so, does it feel easier to sustain this intensity? Now, try altering your position on the bike - how does this impact your SmO2?Whether or not you’re a competitive athlete, you should try this type of to experience how your cadence, breathing, and body position can impact your muscle oxygenation values, even at a fixed power output or speed.
Want To Learn More?
To learn more about about how you can leverage these new innovations in high performance technology you can check out the following articles:
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