Thursday, April 4, 2019

MLSS retest by both blood lactate, Vent and NIRS

In a prior post, determination of MLSS by blood lactate testing was discussed.  Since the last couple of discussions were based on the foundation that I actually had an accurate value for this, I decided to double check (maybe my fitness changed).  In addition, since NIRS metrics on longer intervals seem to give a valid estimation of this, a combined simple two stage test was done.  The idea was to make this as short and stress free as possible.  

Knowing the ballpark MLSS of 250w, the initial interval was 247w for 5 minutes (after a 30min warm up).  Fingerstick lactate was measured with the Lactate Scout within 1 minute of interval end.  The Hexoskin provided heart rate, ventilation rate and the BSX sensor was placed on the L RF as the NIRS choice.

Baseline lactate was 2.2 before starting.

Here is the power profile with heart rate:
  • The first interval was done at an average of 247w, the second about 16 watts higher.
  • Lactate rose from the baseline (2.2) to 2.8mM/L at the end of the first interval.  
  • At the end of the second interval (263w) the lactate rose to 4.8.  This is a positive result either from a fixed cutoff or incremental rise standpoint (.5 mM/L).  So somewhere between 247 and 263 watts is the lactate threshold.

The question now is whether or not there are non invasive parameters that also show this.
  • Looking at the above graph, the slope of heart rate rise for each interval is about the same.
What about ventilation?

  • Here we see that the curve slope is about 3 fold steeper with the second interval.  There is a fair amount of variation within each trial but the trend seems solid.  As per previous discussions and tracing presentations, ventilation rate rise is a reasonable way to track MLSS.

NIRS data:
This was something that I wanted to do carefully since in some of my earlier views a very critical light was put on NIRS being of use in MLSS.  Although those comments are still pertinent, from my experience, if an appropriate muscle is chosen with a good saturation dynamic range and behavior, MLSS seems to be obtainable by longer intervals.  The VL is not a good choice for monitoring despite it being an active muscle in cycling given it's desaturation pattern.  Either the RF, costal or even deltoid are better choices.  In addition, there may be an asymmetry in range front left to right.  My first attempt to look at this was done looking at saturation changes of the R RF and VLHere is my attempt on the L RF which in my case has a much better range of values.  In addition the tracing is of HHb, not O2 sat.

  • The tracing slopes for each interval are easily distinguished and over 10x steeper during the second part.  Surprisingly, the curve slope change is even more pronounced than the ventilation tracing.  However, I would guess that some individuals would have different HHb ranges and curve slopes, so YMMV.  I think a very important issue here is to pick the best muscle group both for the test involved and from the range of value obtainable.

  • A two stage test with 5-6 minute intervals done around my MLSS (16w spread), showed a 2 mM/L rise in lactate, confirming the lactate threshold in the 250-260w zone.
  • The slope of heart rate rise was not much different between zones.
  • Ventilation rate slope change between power zones was visibly different with a 3 fold change in slope.
  • Deoxy hemoglobin slope change of the L RF also changed between zones.  The magnitude was higher than that of ventilation (10x slope change). 
  • However, slope magnitude comparisons will be different between muscle groups and individuals.  One must take this into account when choosing a muscle group to follow.  For cycling, the VL is a poor choice given it's desaturation pattern.
  • At least a 5-6 minute interval is recommended (longer is even better). 

 Lactate related posts

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