Saturday, September 16, 2017

Cycling Intervals Part 2

After the last discussion about cycling interval desaturation observations and conjectures, I was asked several questions.
  • The oxygenation trends through a ride session including warmup, intervals and cooldowns.
  • Possible use of this technology to help alert for over train and over reach conditions. 
  • More elaboration about the fluctuation of muscle O2 during a typical ride, making the absolute numerical reliability problematic.

Oxygenation trends:
Some representative tracings of the L RF of a typical cycling session.
First up is a baseline after 15 min stabilization.  There have been observations made by some that some time may be needed to lead to stable readings (few minutes).  As can be seen the O2 is quite steady.

The value of 56% is actually pretty reliable as a baseline for me at that particular site, +- 2%.

Now things get interesting:
What happens after a max interval of 60 sec, but instead of resting, you continue at a lower level (just barely hanging on since you just did a max effort)?
Here are 2 examples:

The yellow is muscle O2, excellent drop on the L RF(all readings done on this page) for the 1 min max, then despite still riding at 170 watts, the re oxygenation still dramatically occurs (as does THb).  Perhaps a physiologist could mathematically model some parameter from this data, but from a practical standpoint not much can be gleaned(except reperfusion).  

Here is a similar interval, same 1 min max, then 180 watts for 1 min then 300 watts for 1 min.
My take home lesson here is that muscle O2 is not very useful for assessment of fatigue.
Despite being about as exhausted as physically possible (in the name of science), my muscle O2 was near the preinterval value.  So claims that O2 monitoring can help to guide when you are ready to train hard again just don't make sense to me. The published data on using O2 to detect fatigue are mixed as well.  Most report fatigue as an effort is done and O2 drops as a result.  But that possibly is just coincident association since they are normal physiological results that should occur together.  A better study did not find fatigue to be associated:
Our results indicate that for modest submaximal contractions, regional differences in oxygenation are not associated with differences in muscle activation or with fatigue development

Also note that the O2 drop at 300 watts was only to 62%.  This is above my baseline (at 170 it's 56%), and nowhere near what a typical 300 watt session will reach.  It does make one wonder if it was worth it from a training perspective to do that last sprint in view of the perceived stress I felt.

So by the end of the ride, do the sats look much different.  Yes, at a similar power the muscle O2 is higher than when I started.

These observations lead me to conclude that the absolute muscle O2 at any particular time is highly dependent on the time spent cycling, the intervals done as well as "micro environments" within the interval.
On a personal level, subjective feelings and heart rate are better clues as to when to nail an interval again, not muscle O2.

That leads to the issue with overtaining detection.  I did do a pubmed search and found nothing mentioning muscle O2 in regards to overtraining.  There was a nice review and summary of factors that have been looked at in this subject.  Interestingly, they concluded that subjective feelings were the best monitor!
I have looked at my muscle O2 during weeks of performance fluctuation (over reaching) and could not find anything meaningful.  That is not to say that the changes were not there, but since it is hard to get the exact same site every day, the O2 will always be a bit different day to day.  This is not the sensors fault, but an intrinsic limitation of the process.  

Interval Optimization

I am more intrigued with using the sensor for getting an O2 drop with the most efficient way, one that can help in doing more quality work with less subjective fatigue.

Here is another 3 min interval with a ramp up protocol, to equal the usual net average watts I would do. This is similar to the previous post.

What I am starting to look at now is what happens if you start with even lower power.  This was my first attempt.  The 3 min average is much lower than usual, the end power is close to the usual average.  Although it is not as significant a desaturation as usual, this type of interval is not as taxing.  I did this after the multiple ones shown above (including the 1 min max) and I am not sure I was even capable of getting a profound desaturation (from residual hyperemia).  More to follow...

Take away points:
  • Depending on the previously performed exercise, the muscle O2 can be quite different.  Even the pattern can be different- rising O2 when it should normally be dropping (seen after a max effort, then doing a sub max effort immediately).
  • Muscle O2 has limited use with indicating readiness for the next effort.  Practically, heart rate and subjective feelings are better indexes.
  • Muscle O2 has not been looked at in regards to over training.  Subjective feelings are very useful in this regards.
  • More investigation into using O2 sensor technology to modulate interval training is needed.  Optimizing the way an interval is done seems the most logical use of this technology from my observations thus far.  It may turn out to be a valuable tool in proper training program design


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