Tuesday, August 20, 2019

The case of the run away VO2 max

In the last post, the VO2 max curve showed a significant elevation on the final stage.  I originally interpreted this as a manifestation of the "slow component".  However, on looking at this again, I just felt something was amiss.  I decided to ask one of the world experts on VO2 max testing as well as the slow component, namely David Poole.  He was kind enough to look over my data and together we figured out the issue.

Let's go back to the original VO2 ramp over time, with a regression line starting at the first stage and statistically stopping at the point of LT2 (but extending the line to the end of the test).

My question to Dr Poole was - is this a slow component issue, and if so, where do we decide to label VO2 max?

His response was that this is not a typical slow component tracing and he felt that there was an error in the gas exchange data at the end, particularly in ventilation:
My feeling, from experience, is that the ventilations may be either falsely high or that the gas concentrations were miss-aligned somehow with the flow profiles.  I have seen this with some metabolic systems that otherwise function very well up to those high respiratory frequencies.  I worked extensively with  MedGraphics in the mid-1980’s to try and circumvent these problems.  Although I have seen on a few % of occasions with VO2 increasing more steeply at the end of tests, this is not classic slow-component behavior – at least to this extent and with the rapidity yours developed.

This was a very testable hypothesis since I was wearing my Hexoskin shirt, and had ventilation data for the entire test.  I then went back to the last 6 minutes (300w and 330w stages) of the test and compared the Ve data from the Hexoskin (from chest/abdominal expansion) to that of the measured gas exchange.

The gas exchange test:
  • We can see that the ventilation in the blue box takes off midway through the last stage as does the VO2 in the red box.

However, the Hexoskin actually shows the ventilation decreasing at the same point:

  • The bottom line here is that the gas exchange is presumably wrong (as Dr Poole thought) and the VO2 max is at the early part of the last stage (54 ml/kg/min which was what it was officially).

Another lesson here is an illustration of the metoboreflex - a redistribution of blood away from the active muscles (RF muscle O2 saturation was very low) during extreme load as well as perhaps diaphragm fatigue as well (with resultant diminished volume per breath).   

I think the issue has been cleared up and it was an interesting problem to solve.

My thanks to Dr Poole for the help!

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