Monday, November 5, 2007

Power Demands of Cyclocross Racing: Part 1

For the past couple weekends, coach Mike Kuhn and I have had the pleasure of going to some cyclocross races at Lehigh Valley, Fogelsville, Fair Hill and then yesterday at Spring Mountain. Cadence has partnered with CycleOps for these events and CycleOps has generously provided 10 Fluid trainers for riders to warm up on as well as 2 wireless PowerTap demo wheels for riders to use. We have encouraged riders to ride and race on these wheels. Many have never used a power meter before and are curious about what to expect. Others would like to test the durability of the PowerTap wheel in some of the harshest conditions imaginable. Personally, I look at it as a great opportunity to collect data. Though power meters are very common on the road, you don't see too many in cross races so naturally there isn't much out there in the way of literature on training and racing with a power meter for cyclocross racing. Here are some basic stats on some of the riders that rode Sunday's race at Spring Mountain:

Woody: 2nd place in Men's B race
Weight: 175 lbs
Background: Cat. 3 road racer, former messenger
Duration: 44:48
Avg. Power: 271
Avg. Speed: 12.1 mph
Avg. Cadence: 80 rpm
Normalized Power: 297 watts

Johann: 3rd place in Men's B race.
Weight: 200 lbs
Background: Cat. 2 road racer
Duration: 44:53
Avg. Power: 286 watts
Avg. HR: 186 bpm
Avg. Speed: 12.0 mph
Avg. Cadence: 79 rpm
Normalized Power: 316 watts

Chris: 7th place in Men's B race
Weight: 180 lbs
Background: Cat. 4 road racer, Ex-BMXer
Duration: 45:59
Avg. Power: 253 watts
Avg. HR: 180 bpm
Avg. Speed: 11.7 mph
Avg. Cadence: 70 rpm
Normalized Power: 275 watts

Kyle: 3rd place in Men's A race
Weight: 134 lbs
Background: Pro Mountain Biker
Duration: 34:36 (the data recorded is for the beginning of the race... Kyle had a mechanical and had to take a bike change)
Avg. Power: 234 watts
Avg. HR: 182 bpm
Avg. Speed: 12.7 mph
Avg. Cadence: 76 rpm
Normalized Power: 260 watts

John: 4th place in Men's A race
Weight: 160 lbs
Background: Cat. 1 Road Racer
Duration: 1:05:56
Avg. Power: 227 watts
Avg. HR: 175 bpm
Avg. Speed: 12.2 mph
Avg. Cadence: 74 rpm
Normalized Power: 250 watts

Colin: 5th place in Men's A race
Weight: 170 lbs
Background: Cat. 1 road racer
Duration: 1:06:59
Avg. Power: 245 watts
Avg. HR: 187 bpm
Avg. Speed: 12.1 mph
Avg. Cadence: 67 rpm
Normalized Power: 269 watts

Erik: 10th place in Men's A race (also raced in B race)
Weight: 185 lbs
Background: Cat. 4/espoir road racer/track racer
Duration: 1:02:54
Avg. Power: 203 watts
Avg. HR: 187 bpm
Avg. Speed: 10.1 mph
Avg. Cadence: 76 rpm
Normalized Power: 240 watts

For a definition of these terms, look at my last entry on this blog. The first thing that stands out to me about these files is how low the power is. Every one of these riders is capable of producing more power than they did here but the technical sections make it difficult to use that power. A good technical rider will spend more of the time pedaling and less time coasting. Kyle is certainly the most technically proficient of these riders and he is able to come much closer to actually producing the power he is capable of producing. However, it is important to remember that most riders will fade in the later laps of the race so with only 35 minutes of data, Kyle's numbers are most likely a bit high.

The other thing that stands out about these files, at least compared to a road race or criterium is how low the cadence is. This is primarily because a lot of time is spent coasting, usually just before obstacles or technical sections. However, cadence will be lower even when pedaling during cyclocross because a bigger gear will generally make it less likely that the rider will lose traction.

More to come later on how we can use these files to better identify riders' strengths and weaknesses and design individualized workouts and training plans that can help maximize their potential.

Mike and I plan on being at a lot of cross races in the upcoming weeks, so if you are there feel free to stop by, warm up on the CycleOps trainer and demo one of the wheels. Here's the schedule:

November 10th: Beacon Cyclocross, Bridgton, NJ
November 11th: Highland Park Cyclocross, Highland Park, NJ
November 17th: Mercer Cup Cyclocross #1 (USGP #3), Trenton, NJ
November 18th: Mercer Cup Cyclocross #2 (USGP #4), Trenton, NJ
November 25th: MABRA Championships, Taneytown, MD (tentative)
December 1st: Carlisle Cross Classic (MAC #5), Carlisle, PA
December 2nd: Capitol Cross Classic (MAC #6), Reston, VA

See you there!

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5 Comments:

Blogger Chris Mayhew said...

Would it be possible to get the IF's for the athletes? That supplies a lot more information.

Do you think perhaps the low powers are simply based on time off the bike eg running and barriers?

November 7, 2007 at 12:08 PM  
Blogger Mike Kuhn said...

Hey Chris, good to hear from you. Thanks for the great questions and thanks for checking out our blog!

Unfortuneately, since we do not coach all of these athletes and many are trying power meters for the first time at these races we do not have threshold data to calculate IF values. I am sure this is something Colin will discuss as we progress through the season in his continuing series on the Power Demands of Cyclocross Racing.

At the Spring Mountain course I would estimate that the athletes were off their bikes and running for a maximum of 10-20 seconds per lap. While the zeros contributed by the time off the bike to the power and cadence averages will certainly bring both down, the overall impact will be small -- 2 to 3 minutes off the bike over 50 to 60 minutes of racing. We should also consider that the accelerations after the runs are typically high power efforts substantially over threshold and above the averages for the race. These accelerations would contribute an opposite effect on the average and normalized power.

Certainly the more running involved (time off the bike) the more it will draw down these averages.

November 7, 2007 at 5:57 PM  
Blogger Colin said...

Chris-

Thanks for your excellent questions. As Mike said, we don't have Functional Threshold numbers for all of these athletes, and even the ones we do have (Kyle, Colin, John, Woody, Chris) are based on test results during the summer so they may be outdated for November. That said, here are the estimated IFs for the race:

Woody: 0.86
Johann: 0.90
Chris: 0.76
Kyle: 0.92
John: 0.77
Colin: 0.77
Erik: 0.87

As for the running, this would not greatly affect the power averages because of the relatively short time off the bike. There is a setting on the powertap to record data if speed is present or if HR is present, and this could affect the numbers slightly. Unfortunately this is not something we checked before the race. It cannot be ignored, though, that even short runs take a toll on the rider both muscularly and aerobically and will draw down the power numbers a little.

My belief is that there are 3 main resaons for the low power numbers:

1. Very non-steady state effort in cross. Constant coasting/braking then re-accelerating. Most of these accelerations are 3-10 seconds, so generally not enough to drive the Normalized Power very high. (I'll talk about this in the next blog).
2. Because of the technical sections, riders cannot use all of their power, though as I mentioned, the better technical riders are able to get closer.
3. Low cadence. This means more muscular fatigue and therefore an athlete's muscular strength becomes more of a limiter than aerobic capacity.

November 8, 2007 at 8:39 AM  
Blogger Adam Mills said...

The thing we must ALL remember about this is that Cycling Peaks was not designed for CX. I've got multiple clients using power meters for CX and I'm not really using any of the default graphs in CP to quantify the CX races. It DOES NOT WORK! Think about it.... RPE (race)= 19-20, however the TSS and IF are both indicative of threshold rides or less...... You are missing something. Something big. Something very important.

October 12, 2009 at 4:39 PM  
Blogger Colin said...

Adam-

Thank you for your comment but I am having trouble seeing exactly what you are disagreeing with. I never claimed that TSS and IF are good meaures of intensity for cyclocross races. In fact, if you read through the comments you will see that I am saying just the opposite. The normalized power algorithm is based on a 30 second rolling average of power, which doesn't work for cyclocross because most of the efforts are 3-10 seconds. Last fall I experimented with changing this to see if a different duration worked better and I found that using an 8 second rolling average to calculate NP was a much better fit for cyclocross.

It is also important to remember that normalized power isn't perfect. There are plenty of "Normalized Power Buster" files that anyone who has used a power meter for a significant length of time has, but the bottom line is that it's the best we have... unless you can propose something better.

October 13, 2009 at 8:16 AM  

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