Tuesday, October 9, 2018

VO2 max training and trainability

As previously discussed, the VO2 max can be used as both an index of aerobic exercise ability as well as a foundation for training zones.  Certainly, a goal of training is to improve the VO2 max power to be more competitive in racing.  Two major points to be addressed in this post will be:
  • Can VO2 max be improved?
  • If so, how to do this.

Some background first

Form a theoretical standpoint 5 major factors should influence VO2 max:
  • Ventilation
  • Diffusion of O2 across the lung membranes
  • Movement of the bulk of O2 through the cardio pulmonary system (cardiac pump)
  • Distribution and shunting of blood supply to the peripheral muscles, intestines, skin
  • Diffusion of O2 from blood to tissue to mitochondria (and mitochondrial fxn) 



However 2 major factors account for the vast majority of VO2max potential with the others probably important in elite athletes.  The 2 main factors are hemoglobin mass and maximum cardiac output.  

It should follow from this that improving either hemoglobin mass and/or cardiac output will lead to VO2 max enhancement.  

Trainability:
Studies have shown that VO2 max will improve from 0 to 60% after 20 weeks of moderate to intense training.  The increase with training is not related to baseline VO2 max.  The Heritage study showed that 10-20 % of individuals did not improve VO2 max despite moderate intensity training.  This was interpreted as meaning some people just can't train up their VO2 max.  Later work has shown this is simply not true, these "non responders" just need higher intensity, longer duration efforts to improve:
In addition, a meta analysis of interval training programs showed that intervals of 3-5 min (near VO2 max power) produced the best improvements in VO2 max.

Interestingly, the hemoglobin mass was the primary factor responsible for a 6 week training protocol looking at VO2 max in relation to how many training sessions per week:

The conclusion of the above papers is that with sufficient intensity, volume and time, even poor responders will improve their VO2 max.  In addition, a duration of intensity of 3-5 minutes (near max effort) may be optimal.  It is interesting that this is near the test duration of obtaining the maximal aerobic power.  With respect to the specificity concept, training at near the VO2 max would seem to best satisfy that condition as well.  

What about shorter intervals?
A popular training technique is to do repeated Wingate sessions (30 sec all out max).  Does this type of interval reach VO2 max and if so, how long does one stay there?

This study looked at a series of 4 wingate bouts separated by 4 minutes of recovery with a repeat series the following day (SIT2).

The VO2 max (and HR near max) was reached but for only a brief time:

The conclusion was that this was not a good type of training in relation to cycling at VO2 max levels (although it looked reasonable for lactate):


Rest Timing:
Another study looked at cycling 30 seconds at VO2 max, then 15 seconds at a half VO2 max power (compared to constant cycling at the same power but longer times/fewer intervals).  They did get reasonable time above 90% of the VO2 max with that interval protocol:


I did a similar interval scheme and will share my tracings.
The standard 3 min at just above my VO2 max power was done first:

 Costal O2 desaturation was steady and significant.
 Heart rate and ventilation rose quickly and stayed high throughout:


About 10 minutes later a series of 6, 30 sec intervals at about the same power were done.
I was curious about the effects of either total rest or between interval half VO2 max (half MAP-max aerobic power) power so the initial rests were coasting:

The yellow circles show either near zero power or about 160 watt avg.
The costal desaturation does become interesting with the intervals at half MAP, with progressive drops, although the RF is about the same nadir either way.

Heart rate and ventilation:
The max HR did not reach my usual values (as seen with the 3 min effort).
Ventilation rates were not impressive when the rest interval was near zero but picked up (and perhaps would have continued to climb with more intervals) when rest was at 50% MAP.

The deltoid desaturation was also measured:
The desaturation was a bit different than I've seen before, with an initial rise at the beginning of the intensity, peaking at 15sec then dropping (and continuing into the rest).  The initial rise in O2 is reminiscent of what I see on the Costal area during a one minute max, or in the 6 interval tracing above.  I wonder if this represents an increase in venous blood flow return from a strong muscular pump effect in the legs.  The increase in venous return could result in a transient boost in stoke volume, cardiac output.  In any case, like the Costal tracing, the active, 50% MAP rests create a progressive desaturation and higher blood flow redistribution.  The progressive increase in deltoid desaturation argues against the possibility that arm muscular activity is producing a deltoid O2 change since they are of the same power efforts (only the rest is different).  This helps to validate the deltoid area as a reasonable surrogate for cardiac output redistribution.

VO2 max training without power.
I recently was traveling and did not have my usual bike and power meter.  However I brought along the Hexoskin shirt to try to simulate a typical 3 min MAP (350 watt) interval.
The goal was to reach my max heart rate at the end, about 159 at 1 min, near max ventilation at the end (200+) and near max midway.
It looks like I nailed it pretty well!
This physiologic tracing is indistinguishable from one I would do with a power meter (see above).
Having said that, after doing so many of these in the past, my "pacing" is probably good, but this was on a different bike, inside trainer and I was lucky to get it right.  
The takeaway on this is that VO2 max monitoring and training can be done without a power meter with super accurate HR (EKG quality) and ventilation.


Summary:
  • VO2 max is trainable.
  • Some athletes will require more intensity, duration of training to reach their potential.
  • Since the Heritage study did show a moderate "non responder" rate when training at moderate intensity, one could say that moderate intensity is not optimal for VO2 max potential improvement.
  • The optimal intensity may be near or at the MAP.
  • Shorter intervals (although helpful on many levels) by themselves do not allow sufficient time at VO2 max and may not be optimal for this training outcome.
  • Short intervals coupled with even shorter active rest (half MAP) allows training at VO2 max in a similar (or better?) fashion than 3-5 min MAP intervals.
  • One can simulate VO2 max training with accurate HR and ventilation without using a power meter. 

 VO2 max related posts

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