Monday, November 12, 2007

Power Demands of Cyclocross Racing: Part 2

It was another exciting round of cyclocross racing in New Jersey at Beacon and Highland Park this past weekend; both were UCI races and part of the Mid-Atlantic Cross Series. Davide Frattini and Georgia Gould won both days with the right combination of form and fitness. Georgia impressed us all by winning the Men's B race on Saturday and placing well again on Sunday (starting at the back of the field both days) before riding away from all her competitors in the women's races both days.

Last week I posted power numbers for some of the riders that rode with PowerTap wheels in the Spring Mountain race. Just to refresh, a few things immediately stand out about these files:

1. Very non steady-state efforts
2. Relatively low power; far less than what the riders would be capable of producing for a steady-state effort of the same duration.
3. Low cadence. Average cadences were 67-80 rpm.

So what makes cyclocross so hard? It certainly isn't the high average power, or even normalized power. Is it the low cadence? Is it the running? How important is technical ability? Does better technique mean that a rider will not have to put out as much power to go the same speed? And finally, what qualities make a good cross racer?

When you look at power files from any cyclocross race, there are 3 "modes" that a racer will be in almost all the time:

1. Sub-Maximal. This is the point that is just short of a sprint, about a 9.5 out of 10 on the intensity scale. In non-technical sections with good traction and no obstacles, riders can really lay down the power. These efforts can range anywhere from 2-3 seconds up to about 30 seconds on courses with long open sections. In the course of a 60 minute race a rider may have to make up to 200 of these efforts. Though the length of the efforts is highly course dependant, they are rarely over 30 seconds. Since Normalized Power is calculated using a 30 second rolling average, that number will not truly reflect the difficulty of the race like it will in criteriums and road races that include regular 30 second+ hard efforts.

2. Coasting. No power is applied to the pedals. This could occur going down a hill, into a turn or into the barriers. These efforts typically range from 1-5 seconds.

3. Braking. Although braking and coasting will both register as zero power, I will make the distinction here because braking is actually the application of additional opposing force. Remember my definition of Speed = [Power - opposing force]. On a flat road, about 85% of the opposing force is from aerodynamic drag with the other 15% from gravity, rolling resistance and drivetrain resistance. When a rider goes uphill, more of the resistance is from gravity and as they slow down the amount of aerodyamic drag increases. Off road, aerodynamic resistance is minimal because of the slower speeds, but rolling resistance is much more significant. Braking force is rarely considered in road racing because the brakes are used so infrequently, but it is highly significant off road. So maybe before you go on that crash diet and try to lose 10 lbs, you should ask yourself if you could brake a little less, or perhaps not quite as hard.

4. Soft Pedaling. These are the sections that are too technical for a rider to go full throttle, but they can still pedal through. These usually occur around tight turns or off-camber sections of the course. These efforts are usually 3-10 seconds in duration. Power output is typically in the recovery or endurance zones.

What is conspicuously missing here are the long steady state efforts that would occur often in road racing and even in mountain biking.

If we examine in detail the file of a technically proficient rider, you will see that they spend less time coasting and more time pedaling. A good technical rider is still soft-pedaling when others are coasting. This means that they will come much closer to actually producing the power they are capable of (as we saw with Kyle last week).

The other factor is that the better technical rider makes less severe decellerations. Less severe decelleration means that the reacceleration is also less severe. Think of it this way: every time you lose speed through an obstacle you have to get back up to speed after you clear the obstacle. If you don't lose as much speed, you don't have to apply as much power or apply power for as long to get back up to speed. This energy savings adds up. Though some of us have more matches to burn than others, no one has an unlimited number of matches. Every re-acceleration takes energy and causes muscular fatigue, so a rider that is constantly slamming on his brakes and then sprinting back up to speed is at a distinct disadvantage and most likely won't have much left at the end of the race to sprint, attack or chase.

As evidence of this, we can examine a couple close races at Spring Mountain. In the B race, Woody and Johann were 2nd and 3rd, respectively, and finished only 5 seconds apart. Woody, as the better technical rider, spent 8 minutes and 27 seconds (~19%) at sub-maximal power levels (>5.5 watts/kg) whereas Johann spent 9 minutes and 11 seconds (~20%) in that zone. In the elite race, we can examine John (4th place) and Colin (5th place) who finished 1 minute apart. John spent 13 minutes and 10 seconds (21%) at sub-maximal power levels compared to Colin's 15 minutes and 24 seconds (25%).

So, what does it take to be a good cross racer?

1. The ability to make repeated sub-maximal efforts with little recovery.

2. Good technical skills: more time pedaling, less time coasting, less time braking and less severe braking. This of course, should all be done while keeping it upright :)

3. Good muscular strength. This is necessary because of the low cadence/high torque nature of the sport.

Of course, there are other factors as well, such as being able to start a race with a 15-30 second all out sprint, transitioning on and off the bike well, being able to run with the bike, and of course, a lot of mental toughness. Next week I will talk about how we can create workouts and race strategies that will best capture the unique demands of cross racing and help racers minimize their weaknesses and maximize their strengths.

This weekend Trenton will host the biggest weekend of cross racing on the East Coast, so I hope to see you all out there with your cowbells!

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