Deeper Look Through BSXinsight – Muscle Oxygenation


We’ve had a number of requests asking to see the raw data captured by BSXinsight during a lactate threshold assessment test. At the heart of these inquiries is a desire to understand how the data correlates with one’s lactate threshold. Below is a graph with an athlete’s muscle oxygenation (SmO2) recorded by BSXinsight during a cycling assessment test. We’ve overlaid that with the blood lactate (BLa) results from the same test.

Before we start I want to first say that BSXinsight does not measure your blood lactate concentration. It measures the change in muscle oxygenation.

Muscle Oxygenation vs Blood Lactate

In this blog post I’d like to briefly talk about three of the immediately apparent segments in this SmO2 profile, and touch on the physiologic events associated with them, in addition to the relationship between SmO2 and BLa during these times.

Taking a look at the overall trend of the charts you will notice the first segment of the blue SmO2 graph has a relatively steady baseline, then a slight curve, followed by a sharper inflection point. During low intensities of exercise, your body experiences a series of physiological changes as it goes from a relatively sedentary state to an active one. These changes begin the process of providing working muscles with an increased distribution of oxygen. The flat region in oxygen saturation (SmO2) corresponds temporally with that of blood lactate (BLa), in which there is very little change, and together these correspond with predominantly aerobic exercise. This means the workload is low enough for your body to produce sufficient oxygen to your muscles for its energy demands. As a result, during this same period of time blood lactate concentrations remain stable. As long as the body’s lactate clearance mechanisms exceeds the rate of production, there is relatively little change with each increasing intensity stage.

As the exercise intensity increases further, the rate at which your working muscle consumes oxygen increases to match the demand. At some point the stable balance between delivery and utilization is tipped and your body requires more oxygen than can be provided. This produces a visible desaturation, or downward flexion of muscle oxygenation. Similarly, as your body’s energy demand continues to grow with an increased reliance on the anaerobic system for energy production, lactic acid is produced in increasingly greater quantities. This can be seen with a slow increase in blood lactate.

As you approach your lactate threshold, the increases in lactate becomes more rapid along with the decrease in muscle oxygenation. At this level of exertion, your body has now become heavily reliant on the anaerobic systems. Maintaining or increasing the intensity of exercise will result in eventual exhaustion or “hitting the wall”. This inflection point seen in muscle oxygenation trends is what has been correlated with the blood lactate threshold at BSX Research Laboratories. To know more about the process we went through in building our algorithm read our Validating the Algorithm blog post.

The training implementations with this technology and data are immense, and continue to grow. The ability to track your body’s physiologic state in real time will allow you to take your training to the next level.

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14 comments on “Deeper Look Through BSXinsight – Muscle Oxygenation

  1. With some team time trials coming up later in the season I can see real time data being very useful in planning strategy and when to switch riders.

  2. How it comes that you placed BSX on the calf muscle? What about Hamstrings or Quadriceps? Is there some physiological explanation ?

  3. “The ability to track your body’s physiologic state in real time will allow you to take your training to the next level.”
    Am I missing something here? I want to track my SMO during time trials but I cant find how to do that in the app. Also, I notice that the threshold calculated by BSX is lower than that calculated from my power meter using trainer road and lower still than my performance in time trials where I seem to get to steady state sooner than indoors and can maintain power for longer. Are you suggesting I should lower my training zones?

    1. Mark, we are currently working on that feature and hope to incorporate it into the app soon! We haven’t had the opportunity to look at Trainer Road and see how they calculate training zones, so I couldn’t give you any reason why there is a difference.

      1. That’s great news. I will continue using BSX to test every few weeks and see how the LTHR FTP and training zones stack up against my performance in this seasons time trials.

  4. Thanks,

    Are you able explain where it you have derived the values for the SmO2 % in the graph above?

    Does the algorithm predict the starting level of SmO2 from a average resting muscle level and then plot the relative change in SmO2 from there as the exercise onsets?

    1. Vince,

      We’re currently in the process of building out a FAQ section that will go into more detail about both of your questions. At a very basic level, yes you are correct. However, there are many additional factors that go into the SmO2 readings than I can discuss at this time.

  5. Hello. What threshold value / method do you use to determine (define) the LT? 4 mmol / Dmax ..?

    Where is the % SmO2 based on? That is what does the nomintor and what does the denominator contain?

    1. During our lactate threshold testing we used 1 mmol followed by another 1 mmol increase in blood lactate. We then used that data to “train” our algorithm.

      That is a very insightful question and appreciate you wanting to know more about how BSXinsight works. Currently we are building out a knowledge data base (both here on our blog and a FAQ section on our website) that will answer those types of questions in detail.

  6. What is the strength of correlation between the LT determined by smo2 and Blood lactate. Also what is the method you have used in this test to determine LT?

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