Monday, July 11, 2011

Nature Valley Grand Prix St. Paul Criterium, When Numbers Alone Can Lead You Astray

Sometimes, looking at numbers can give you a realistic idea of how hard an event is.  Using Intensity Factor number from Training Peaks helps us to understand and quantify the difficulty of the event.  Coupled with the Training Stress Score, and normalized power an experienced exercise physiologist and coach can realistically estimate how tough any particular ride or race was.

But what happens when the numbers just don't add up?  For each event, Source Endurance consultants make it a point to engage every athlete in some way to get a report/ debriefing of how it all went down.  This usually occurs during the scheduled consult.

A few weeks ago Shadd Smith competed in the Nature Valley Grand Prix (NVGP) Stage Race.  Following each stage Shadd would upload his data where it would be examined and scrutinized.  The numbers tell one story.  However, when coupled with the daily race summaries provided by Shadd, an entirely new layer of data comes to light along with some new realizations of the limits of human physiology.

In the picture below, you can see the non-smoothed race in its entirety.  The first thing that comes to mind is that it looks almost like there are attacks the entire race.  But wait, is that true? I've drawn two lines; one at Shadd's threshold and the other is at 600W.  This wattage seems to be a good measure of how many top-end efforts an elite athlete makes.  To put it in perspective, an amateur race with nine +600W efforts in 5 minutes can cause a irreversible split in the field. 

At the NVGP, Shadd produced around 15 of these efforts per every five minutes for over an hour.  All while the United Health Care Team (UHC) rode "tempo" on the front, meaning that not only was the field not splitting, Shadd was actually just sitting in the wheels, a testament to the difference between amateur and professional racing.

Towards the end of the file, you'll see where Shadd was finally unhitched, along with nearly every other rider in the field as UHC began the lead out.  This led him to ask the question, "if the normalized power from the race was significantly less than my threshold power, why did myself and so many guys get dropped?"  Indeed, even with those high power spikes, the normalized power was only 299W for the entire race.  Let's investigate..... 

Below you see a smoothed version of the same race.  Notice how the speed and power are very cyclical, indicative that not a lot of attacking is going on.  Rather, because of the UHC escort, the race was just fast, all the surges were mostly likely accelerations coming out of corners as well as the energy required to improve position.  You can see that toward the end of the race, the pace begins to edge upward.  With the accumulated fatigue from the day's efforts, this proved too much for many riders, amateur and professional.
His output numbers for the event are well within his ability level, by the numbers.  How would it be possible to gap off that many excellent riders?  To get a better view, we'll examine the non-smoothed, zoomed in view of a ~5min block of the stage.

Confirming the previous conjecture, it does appear that cyclical peaks and valleys are a product of the race course which required slowing for turns, then accelerating back to speed.  However, you'll notice the large bit of time where the is no power production, or very little. That little bit of rest, that coasting is a godsend in the short term.  The opportunity to recover just a bit makes the prospect of what is to come just a bit more bearable.

However, the coasting is also the root cause of why so many PRO and elite riders were sent home that evening with a time loss.  In order to coast for ~38% of the race and maintain a normalized power of 299W, there must be some hard efforts, and many of them as you'll note from the amount of time spent over 600W.

This brings me to the issue of recovery.  For every effort, there is a required recovery period.  As the intensity rises, recovery time increases.  However, at some point, or perhaps always, this recovery time appears to increase exponentially or at least in a non-linear fashion.
For example say at an intensity of 200W the recovery time is at a 1:1 ratio. 
300W, 1:1.5
325W, 1:2
350W, 1:4
375W, 1: 8 and so on....

This could explain how a race that appears very benign "by the numbers" was in fact one of the hardest races Shadd has ever completed.  However, without the race summary from him and the post race consult, any coach and many exercise physiologists would have a difficult time understanding this race and why the athlete, Shadd would find such a race so hard.