Monday, February 1, 2016

Go Fast When the Race is Slow - A Case Study

by Alan Couzens, MS (Sports Science)

A bit of a departure from my series on flexibility this week to indulge one of my guilty pleasures: Power File Analysis!

In April we were fortunate to have a number of ECers and friends of EC racing the Oceanside 70.3. A group of these came in with quite similar bike splits and seemed like a great opportunity for a case study.

In training, the aim is always to build the greatest power over your race duration but on race day, that emphasis changes to getting the most speed for the power that you’ve built, that is, being as efficient as possible with the power that you have. I chatted through some theory on the best way to get the most speed bang from your power buck in my "Know Your Enemy" series. But in this piece I want to put theory into practice and look at what speed differences are actually created by different power distribution scenarios.

In terms of getting speed from power, two big factors come into play:

  • Aerodynamics
  • Power distribution

In this article I’m going to focus on the latter of these and see if we can tease out differences in speed from different power pacing strategies.

As I suggested in "Know Your Enemy," when it comes to speed, not all watts are created equal. The percent speed difference between 200W and 300W will be significantly greater when relative air speed is low, such as when climbing a hill or when being pushed along by a ripping tailwind. The clever athlete can exploit this by, as Robbie Ventura calls it “going fast when the race is slow,” resulting in more overall speed from a given amount of watts.

The opportunity to look at six athletes going similar speeds on the same course but with different power output was too good to pass up. Thanks to Chris Hauth, Albert Boyce, Mark Pietrofesa, Greg Penner, Paul Linck and Gordo Byrn for offering up their power files for this piece. Let’s dive right in and take a look at power and speed for each of the guys on the Oceanside course.

Now, of course, body size does come into play, especially on a course with some solid hills like Oceanside so let’s look at the weight of the guys and the data from a watts per kilogram perspective.

As an aside, looking at the data from a pure w/kg perspective is being generous, as speed has been shown to be related to w/kg^0.32 for relatively flat cycling and w/kg^0.79 for climbing (Padilla, 1996, 1999). So, everything being equal, we would expect the heavier guys to outperform the lighter guys at the same w/kg on anything but a straight up climb.

That's quite a range of relative power numbers there for folks going a similar pace. Looking at each pair of athletes individually yielded some obvious differences in aerodynamics when I compared two athletes putting out the same relative power but going very different speeds on the downhills and flats (for example, Paul versus Mark). Nothing particularly revolutionary here: he who produces more power or exposes less frontal area to the wind, wins!

However, the really fun stuff comes when we compare two athletes who got similar speed out of their power numbers when they were equal on the downhills and flats but who chose to distribute this power differently for the bulk of the race and got some different results. Albert and Gordo fit the bill for two athletes who had similar w/kg numbers and similar watts:speed on the flat but different overall results. Let’s take a look at their files in a little more depth…

Even with a busy chart like this one, it’s clear to see the differences in pacing strategy. Gordo hits the first rollers very hard with two periods at or above his FTP of 4.05 w/kg and then a solid period just below his FTP before "shutting it down" to 80% of FTP for a significant portion of the race (25-39K). A period of about 20 minutes that allowed him to metabolize the majority of the lactate produced with the earlier efforts. This section of the race also happened to be the fastest (41.5km/h). He then regroups and comes back with FTP+ efforts for the two significant climbs before dialing back to about 70% for the descent and finishing the flattest portion of the race close to the race mean of 3.6 w/kg.

Albert has a much more even distribution of effort (VI=1.05 vs 1.07), with significantly more power output on the rolling downhill section of the course (km 25-40) and a little less on the climbs. Albert puts out 4% more relative power than Gordo on this section – 3.5w/kg versus 3.35w/kg, while Gordo puts out about 11% more power (4.1 versus 3.7w/kg) but for shorter periods on the climbs.

So, who gets the most bang for their buck? For his 4% greater power outlay from km 26-40 Albert gets 1% greater speed than Gordo over that high speed section. For Gordo’s 11% additional outlay on the climbs he gets 13% greater speed, resulting in a 5% faster total speed over the whole course.

Basically the same power output but distributed differently yield different average speeds. The message is clear. If the aim is to produce the fastest possible overall speed on the power that you have – go fast when the race is slow.

Train Smart

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