Thursday, June 21, 2018

Fast Start Strategy and O2 monitoring

We all know that professional cyclists (as well as enthusiasts) will go to great lengths to shave a few seconds off a given course.  Thanks to nuances in bike tech and aerodynamics many advances have been achieved.  However, another factor that is generally not thought of affecting course completion time is the pacing strategy that is employed.  Pacing choice can be looked at from two different realms, one physics and the other physiology.  Studies have been done looking at the time saved by riding a bit harder up hills than down, and it is not trivial.  From the standpoint of exercise physiology, there may be benefits to whether one rides at an even pace of power or not.  So instead of cycling at 300 watts for 10 minutes, one could start with using more power, or start with less and have the same average power at the end.  The question then becomes, which method (if any) yields the best average power with the same effort or the fastest time at maximal effort.  This has been examined in both running and cycling.  This post will address the literature and some of my personal experiences with the different power start strategies.
To begin with, I stumbled on this subject purely by accident. Recently I was doing one of my usual "drop the rider" intervals.  The first 100 second piece was done at about 400 watts and as costal O2 dropped into my caution zone, power was reduced to about 280.  Instead of stopping at 3 minutes total time, I felt pretty good and just kept the same pace until the 5 minute mark.  Despite still feeling decent at that point, the average power was a personal best by far.
After a 2 day rest, I cycled the exact same course again but at a constant power within 1% of previous.  Although I was fine at 3 minutes, by 4 minutes I was starting to suffer.  At 4:30, I was ready to quit but wanted to finish in the name of science.  The end RPE was off the charts and costal O2 near historical lowest value.

This result is not surprising given some fascinating studies that have been done over the past few years. In a comparison of fast start, slow start and even start power pacing, the fast start strategy is usually associated with the best overall average power in the range of 1 to 6 minutes. The theory behind this is that starting well above the critical power speeds up the kinetics of reaching your VO2 max. In fact riders using the fast start method will consume more O2 than the slow/even start approaches. Whether or not this helps save anaerobic resources later in the effort is not clear.

Here is some data from an early study looking at the slow, even and fast start pacing with a 3 or 6 min time trial.  The trial was ended in each instant by a short sprint.
The exact power profiles were:
 
One of the parameters looked at was the MRT, mean response time of the VO2 max:
The results show that the fast start protocol lead to reaching VO2 max faster as well as improving the MRT:

Total work done was improved in the 3 min trial but not the 6 min one:
More recently the same group of investigators looked at a simulated 4km time trial with either an initial all out 12 seconds or just selt paced.  They also looked at the effect of "priming", which is adding an intense warmup interval before the bout.  The priming could be somewhat equivalent to a good warm up with some hills if you are trying this out for yourself.
As before, the fast start (all out) lead to faster VO2 kinetics and more O2 consumed.

The O2 and HHb tracings of a muscle (?vastus?) were also looked at:
There may have been a quicker desaturation in the fast start and primed groups.  However the amount and degree are close to noise levels of O2 sensor day to day variation to be of practical use.

The combination of using the fast start strategy with costal O2 monitoring may be a superior technique to maximize speed and average watt output in short time trials and parts of a longer race.  There have been some interesting proposals in modeling power reserve based on physiological parameters.  Perhaps in some later posts, this can be discussed in more detail.  What I would like to do here is just present some data and hope that other folks can try this for themselves and perhaps report back if it leads to better results.

Now for some of my personal observations.  To preface what is to follow, these were not done with the method above.  The intervals were all preceded by an hour of warm up including hills.  This could be similar to a "primed" strategy but since on a practical basis, everyone is going to warm up before intense efforts it seemed reasonable to do it this way.
The course, conditions were as consistent as possible (same hill, time of day, temp).  When the intervals were done I did not have a plan of testing prospectively.  For most of the tracings, the goal was to reach a near peak average without totally wiping myself out since I still needed to ride home about an hour away.  

Therefore, another way to look at the potential benefit of optimal power pacing (and VO2 max on kinetics) would be to minimize negative factors leading to fatigue and failure to maintain performance.  Hopefully by optimizing VO2 max, anaerobic reserves can be saved for later on, as well as minimizing the buildup of fatigue associated substances.

Cycling:
The first set of comparison tracings to be discussed are 5 min intervals, Fast vs Even start.  To begin with though lets look at a previous "even effort" at slightly less power:
The costal O2 does drop significantly but there is only a slight drop at the end and not into a zone of concern.  This degree of drop would be consistent with continuing the ride without major impairment

The Fast start:
The initial costal O2 drop from baseline is not much different than the even start despite 100 watts extra average power.  As the O2 sat dipped below 30%, I backed off to my 10 minute pace or so.  Costal O2 rose a bit before a slight dip at the end.  The deltoid data was very similar and rose promptly after pedaling stopped.  Avg speed was 20.6The costal O2 saturation was similar to the 307 watt average and performance was not impaired after.

The Even start:
The costal O2 drops initially (although slower), and continues especially the last minute.  The last 30 seconds were quite difficult with a max RPE.  Deltoid tracing was very similar.  The costal O2 was near my nadir at the end.  As expected, the interval "cost me" significantly and I had reduced ability for the rest of the ride.  If this was a race situation I would have probably just dropped out.

The following are the tracings for the VL (a bit noisy on Fast start, also Tot Hb shown):



There does not appear to be any major difference in degree of relative desaturation.  The tot Hb does rise a bit initially in both tracings, perhaps from venous outflow compression.  It then drifts back down to baseline.  Despite the massive reperfusion and VL O2 overshoot, little is seen in the Tot Hb rise, making this a mediocre marker of flow (unless flow was going elsewhere).

What about at 3 minutes duration? 
Here I have many samples (the 3 min interval is my standard test I do 2x/week) but will only show 3 representative tracings of the Fast, Slow and Even starts.



Given that the 3 min average power is the same in all, there are some interesting differences.  As a preface, these do not represent an all out maximal effort, but a near max over the exact same hill.  Both the Slow and Even starts show a gradual decline on costal O2 sat.  Special attention is made to the 10 seconds or so after the pedaling stops with the circle in green.  In the slow start there is a continued fall even with coasting.  I have seen this with post 1 min max intervals possibly from severe acidosis, continued high work of breathing leading to persistent costal muscle use and hypoxia.  This was not seen in the Fast start.
Despite all three intervals delivering the same average power, the costal O2 status at the end is quite different.  In the Slow and Even trials, the O2 curve is downward, and would shortly reach an unsustainable nadir.  Here is a typical all out 1 min costal tracing showing what happens if the O2 keeps dropping.  
There is a steep drop (after a mild rise) and the desat continues to drop to nadir levels after the interval (green marker).  The power of 235 was the best I could do at that point and was forced to stop pedaling after 1 minute.

With the Fast trial, the O2 does drop at 2 minutes or so, but begins to come back up into a more steady state zone that potentially could continue.  A potential usage of costal/deltoid O2 monitoring is avoiding that steep drop into the untenable zone, thereby optimally judging power vs time vs ability to continue.  As mentioned above, I personally was in much better state after finishing the Fast start, confirmed by the higher costal/deltoid O2 values.

The studies do make a point that the Fast start strategy may not be effective for durations longer than 6 minutes (or even at 6 min).  I decided to take a look at this as well. Same course, time of day, temp.

My conclusion was that at similar RPE, costal O2 curves, I was able to get another 14 watt average, basically from the first 60 second fast start without harming my ability to perform an intense effort.  Incidentally, the Fast start 8 minute average above was a personal best over the past 20 years (yes I had a Powertap back then), and I was not even trying to do that.

The bottom line here is that at least for me the Fast start strategy seems to work over the span of 3 to 8 minutes potentially by speeding VO2 on kinetics.  After the fast start is over, continuing on at a stable power that keeps costal O2 from bottoming out seems to be effective.  Of course, if this was an actual race, running the O2 down at the end with a sprint or just keeping the pace higher throughout would yield a better time.

Running:
I asked my friend the cross country skier to try the slow, even and fast approaches as well.  He kindly ran 2 sets of the 3 different pace patterns on a 1 mile track.  He has done extensive physiological testing and knows his lactate numbers pretty well.  He did one set at a power associated with a lactate of about 2 and another at a power equivalent to 4 mmol lactate.  Power was measured with a Stryd and recorded on his Garmin watch.  I plugged the data in at cyclinganalytics.com.  Both the time splits indicated by the Garmin watch, as well as manually highlighting the time under power were determined.  The average power readings were within a percent or 2 in each set.
Here are the "lactate 2" power intervals:
Both the manual measurements as well as the Garmin watch splits indicate the Fast start yields the shortest duration to the mile run.

Next, the lactate threshold run:
The Fast start "wins" by both estimations.  As in my tracings, this does not represent an all out maximum effort, but a significant amount of power near max. Measures of the speed/distance covered showed improvement seen with a Fast start protocol.  One could argue that by using the Fast start method he is getting a faster time without negative physiologic impact.

We also have some VL O2 saturation data that is of interest:
The Fast start tracing has a faster desaturation pattern that remains stable.  Whether or not this is an indicator of better O2 extraction, is hard to say given lack of knowing the blood flow (not tot Hb).  What we can say is that the curve is different than the Slow/Even pacing pattern.
Although this is only a brief look at data without rigorous statistical validation, the results are intriguing and seem to agree with the literature (except for the time of 7 minutes being longer than the study addressed).  My cycling data was done for a fixed time, the running tests were done at fixed distance.  However as shown below the new priming and pacing study did show better time to completion with priming and all out fast start:


Physics
Terrain/Wind considerations:
There is an additional practical consideration when employing a fast start strategy, namely aerodynamics, wind and climbing. In a very elegant study of physics in cycling, modulation of power based on terrain will yield tangible time trial benefits:


From the paper:
Swain (1997) used the equation of motion of a cyclist presented by Di Prampero, Cortili, Mognoni, and Saibene (1979) to model performance on undulating and windy time-trial courses. Faster times were predicted when a cyclist increased power in slower uphill or headwind sections even if this higher power was compensated for by reducing power in faster downhill or tailwind sections so that total work done was unchanged. 

Adopting a variable power profile based on terrain/wind can improve time trial results:


 And the net results in a simulated 40 km TT:
I underlined the curves for different power averages.  Interestingly, the least time saved was in the intermediate power group, the most in the weak riders.
The authors concluded that this type of intervention was potentially worthwhile compared to other methods:

An obvious extrapolation is to combine elements of fast start with terrain/wind considerations to fully optimize a time trail, break away or ascent.
Going back to my 5 min Fast vs Even start tracings (the second and third of my data graphs), the initial 2+ minutes are up a hill (encompassing the Fast start distance).  The Fast start average speed was 20.6 vs 19.8 mph with an Even start at the same net power.  Interesting.



A last comment:
A model of athletic performance was recently discussed in regards to Chris Froome's power profile in various race situations.  This model does not incorporate any power modeling VO2 alterations (especially fast start) in the equations and discussion.  There is also a significant degree of variation in each assumption that could add up to some major significance.  So when modeling such as INSCYD is presented, it may or may not be precise for the given athlete.  Using this approach to provide a clue to doping, motors and such can be very problematic in my opinion.


Final thoughts:
  • A fast start strategy can lead to faster "on kinetics" of VO2 max, allowing a higher power to be averaged over a duration of 1 to 6 minutes (perhaps longer) at max effort or the same average power with less negative physiologic impact.
  • The use of either costal or deltoid NIRS monitoring may help indicate the degree and duration of each segment of the power partitioning strategy to inform the rider how to proceed in real time.  Avoidance of a given riders' personal nadir costal/deltoid O2 range would best allow them to continue at optimal power levels.
  • Consideration of the terrain and wind conditions may also play a role in longer time trials for best race times.
  • Athletic modeling should take into account the actual tracing of power since starting strategy alters VO2 max assumptions.



 VO2 max related posts

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