Monday, August 20, 2018

MLSS +10 watts, a journal review plus personal data

A couple of posts ago the effects of cycling at MLSS plus 25 watts (10%) was discussed.  Recently a study was published looking at the effects of cycling at MLSS plus10 watts (3-5%).  I am going to go over some of the details and findings.  I would also like to express my appreciation to the team of researchers who did this valuable study.

One of the reasons of doing this type of study is that the steady state maximal power definition is just that - steady state.   It is well recognized that power just above this leads to decompensation, acidosis and shortened time to fatigue.  In practical terms, avoiding power in this region for extended time could be a priority in a given race.  

One of the conclusions of the study is the fact that once the MLSS+10 trial was done, the subjects were "spent" and had limited reserves for available power/time.  So not only is it important to know your MLSS, but it would be quite helpful to monitor some sort of response in real time to prevent the beginnings of decompensation.  In terms of getting an accurate MLSS, the study team did multiple 30 min time trails with blood lactate measurements.  Even so they estimated that the error could have been near 9 watts.  Given the precision needed, encouragement is given to readers to use the MLSS method in a previous post that combines limited testing, no 30 min intervals, but excellent accuracy.  From the monitoring standpoint, the use of NIRS, resp rate/ventilation, and heart rate overlaps what has been discussed here.  Surface EMG and metabolic cart parameters were also done.
The basic procedure was for the subject to cycle at 30 minutes at either the MLSS, MLSS+10w and then do a time to exhaustion trial (after a 3 min rest then riding at 80% peak PO).

The Data:

Muscle O2, measured as deoxyhemoglobin:

Interesting observations:
  • The pattern of desaturation is different in the RF and VL.  The VL reaches a maximum desaturation within 5 minutes and remains levels whereas the RF continues to drop throughout.
  • The VL desat is therefore not helpful in demarcating these zones.
  • The RF desat is theoretically helpful but on a practical basis (with measurement changes from sensor position, temperature, hydration) is probably not useful in real time.  In other words if I was on my bike I could not easily use this to stay out of MLSS+10.  The 3 point change may be lost in the noise.

Heart rate:

A slight but significant change in HR.
But can it be reliably used in the field given drift, temp, hydration?

Respiratory rate and ventilation:

Both ventilation and respiratory rate show a large differential between MLSS and +10w.
Although not something routinely used, a very intriguing potential modality to employ in real time.  Also reminiscent of the MLSS and MLSS +25 watt comparison I personally did.

Here is an interesting look at the end trial, time to exhaustion stats:
The lactate, HR, RPE were the same in each end of TT "sprint".
However, both the RR and ventilation were down in the MLSS+10.  According to the authors of the study, the drop in peak ventilation may have simply been due to the decrease in exercise time preventing the subjects from reaching peak VO2 (from fatigue). 
However, despite them not being able to reach full potential exercise time, the HR and lactate were similar.

Finally, the bottom line-Time to exhaustion

The MLSS+10 caused a significant post interval decline in time x power.
This is certainly something we would like to avoid.  Imagine doing a great breakaway, only to have "nothing" left at the end.  

After reading the above study, I wanted to look into the effects of a MLSS+10 interval that was longer than the one I did for the lactate threshold testing.  I was hoping to see similar data as well as the post interval fatigue issue.  After a 1 hour warm up, I did an almost 11 min MLSS+10 capped off at the end with about 16 seconds max power.

  • The costal muscle O2 fell but did remain somewhat stable as did the RF and VL.  
  • Both the RF and VL were capable of a further drop at the end with the short max sprint.
  • The costal O2 did nosedive quickly from the 16 sec max effort.  This drop is much faster/deeper than it usually is, possibly because the respiratory muscles are already fully engaged and at their point of decompensation as well.  This was born out by the next figure, with the minute ventilation already approaching near max levels.
Now the respiratory data using the Hexoskin:

  • The heart rate remained in a stable range till the end (with the sprint).
  • Ventilation rose and continued to rise especially at the end with the max effort.

  • The breathing rate was about the highest I've had.  
  • Despite the very high rate, the ventilation was not at maximal until about 10 seconds later.  The respiratory rate had dropped back down somewhat but ventilation was actually higher.  Whether this is related to respiratory muscle fatigue (and hypoxia), inefficient shallow breathing is not clear but it is a pattern I have seen at the end of intense efforts.

Now for the post MLSS+10 "time to exhaustion" equivalent.  Instead of doing the study TTE protocol, I just did my usual 1 min max effort up the same hill I always do on my way home (for better comparison to previous efforts).  I usually average 510 to 540 watts, and that is after testing various intervals.

The 470 watt average was the lowest I've seen in many years.  The initial 10 second average power was almost 200 watts lower than my previous trek up the same hill last week. That 1 min max was still after doing a 5 min fast start intense interval (but not 11 minutes).
In short, the 11 min MLSS+10 resulted in severe deficits in performance later in the ride.
Here is a graphic of best ride average power this month vs today.  The 11 sec average is proportionately worse than the 1 min.

The costal O2 did drop nicely and I possibly could have pushed out a few more percent if I kept going another few seconds.  So despite the loss of peak and average power, the respiratory muscle hypoxia, cardiac output redistribution was still present, although possibly a bit less.

The Hexoskin data:
  • The max heart rate is near my usual peak (169 vs 171), the respiratory rate and ventilation both rise steadily with no "blips".  
  • The ventilation "efficiency" tracing looks great (did not have that paradoxical high rate but low ventilation volume) yet the average power was poor.  As in the above MLSS+10 study, the legs just did not have the ability to get to the point where respiratory fatigue really set in.  There certainly was a credible change in metrics, but not to the point where respiratory muscle fatigue became a major factor.

Takeaway lessons:
  • The difference in riding at MLSS vs MLSS+10w leads to several physiologic parameter changes.
  • Although HR, RF HHb/SmO2 show some small differences, they are unlikely to be of major help in a real time riding situation.  The VL does not differentiate between these zones very well.
  • Costal O2 is helpful in other interval and pacing strategies, but it does not seem to have the fine discrimination at MLSS+10, at least for 11 minutes.  It is possible curve shape would change at longer effort times.  However for this to be useful in pacing, we would want it to show evidence well before getting to the point of fatigue.
  • The minute ventilation is the parameter that can be measured in the field that best distinguishes the two zones (also seen with the lactate threshold test).  The steady rise of ventilation to near peak levels seems to herald the loss of steady state.  This makes sense as the disproportionate increase in ventilation is largely due to acidosis buffering.
  • In the post interval time to exhaustion bout, the ventilation actually dropped in the MLSS+10, probably related to the subjects just not able to push themselves long and hard enough.  In my example, the ventilation, respiratory rates rose with a post MLSS+10 effort.  However they did not show the fatigue patterns seen with optimally powered intervals.
  • The time to exhaustion is reduced by riding at just 10 watts above MLSS, with the practical implications easily realized.
  • In my case, a timed interval done with maximum power was reduced in both peak and average wattage.

Lactate related posts

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