Road race vs Cyclocross Race Power Comparison
Comparing Road to Cyclocross Race (a power perspective)
Alright gents. This year I got a power meter on my cyclocross bike so I could see what the races looked like. After my first year of racing I had some questions like
OMG why is Cyclocross so hard?
How do I train for Cyclocross?
How much power am I actually doing in a Cyclocross race?
In this post I will try and answer why a Cyclocross race is so hard.
The Power Analogy
Power = force X distance – it is how hard you push on the pedals. W’ or watts prime, is how much power you have in your battery before you collapse in a heap on the side of the road and cry. Put another way, it is an estimate of the amount of power you can do over a given time before you die. The measurement is joules. This is all based on your functional threshold power (CP60) which is how much power you can do for an hour.
Imagine that you can put out 300 watts for an hour and 380 watts for 5 minutes… There is formula, which I can’t find, but it will calculate your W’ to be 24,000 joules. Thats a lot of joules mang!
Now, based on your physiology and fitness, a certain point below your CP will be your break even point. Lets just say that this break even point is 225W. If you did 225W evenly on the bike, theoretically you could go forever because you’re not draining your battery. The rate at which you regenerate is the same your usage.
Alternatively, you do 400W…this is above your equilibrium wattage so you’re using your battery. If you can do this for 6 minutes you might have used up all your energy. (W’ is zero) Lets look at a chart of me doing some intervals.
First of all, this was my first time doing these intervals. These are 20sec hard, 10sec rest X 7, rest 5 minutes and do it again. I had no idea what power to shoot for. I started at 600W and ended up decreasing a little bit. Ideally, your power will be steady for all 7 intervals. In the future I’ll try for 550W.
Regardless, here is the WATTS chart, see the downward trend? Again, not ideal but my point can still be made.
Here is the W’ chart – my W’ fresh is set to 29kJ.
As you can see, each interval, which is done at 150% or more than my CP, takes some of my battery. Further, the 10 second rest (which I still had to pedal) did not replenish my battery to 100%. The result was that I only had 4.9kJ left in my battery at the end of 7 intervals. This is a pretty good interval session because anything less than 7.25kJ is considered Severely Fatigued!
After the intervals I do a light spin until I feel good to go again and then I hit it. As you can see, even though I felt good to go I had not returned to full battery. In reality, if you burn matches like I’ve done then you will never return to full strength but that’s another topic. The interesting thing though is that after about 10kJ I start having issues generating the power to drop it further. Lactic acid in the legs and troubles with the mind contribute to this. I end up only getting to 7.7kJ left in the tank.
Whatever dude how does this apply!
Ok, so hopefully you understand a bit of what is going on in the chart. Now, in a road race you have key moments but otherwise can chill out and draft people. Actually, the whole strategy is to conserve your power and only use it when absolutely necessary, for instance to get over a climb with the leaders, to bridge a gap, or launch a sprint finish.
Here is my chart from the Gorge Roubaix which featured a 7 min climb at the beginning followed by a 25 minute climb further in the race.
At the beginning I did a little action off the front but returned to the pack for the climb. After the first climb I recharged going downhill at the back of the pack. I felt good and actually solo’d off the front at the base of the second climb for about 10 minutes. Unfortunately, I got caught and then dropped by about 10 guys before the climb ended. As you can tell, I dug deep though. At 8.2kW I finished the climb and started chasing to get back on. At about 3kJ I gave up and finished the decent “recharging”. We picked up a few guys going into the finish and I attacked with 1km to go…draining the battery to 7.9kJ before the finish.
Contrast this with a cross race – Heiser Farms CAT 2/3.
The race is much more jagged, not ever fully draining the battery. This is because power is off/on in a CX race. You don’t pedal through every corner or downhill. You get off the bike too (which is zero power). The result is that you will likely maintain a closer distance around a W’ average for the race. This is essentially how well you can deal with the pain in your legs.
The first lap is hard, getting to the front and establishing position for the race. It drops me to moderately fatigued. At this point though you see what happens…things get hard and I’m no longer draining the battery further. Sometimes it feels hard and you don’t want to push, but other times you get stuck behind someone and don’t feel like you can pass them with the power you have left in you or you fear if you do you will blow up.
Cyclocross feels harder than a road race because you’re always putting power down in a fatigued state. This was probably obvious to you prior to reading this but now you know the data behind it.
Therefore, the goal of your training should be to learn to lay down power in the most fatigued state you can sustain for a given race time. For the chart above, once the first lap is done I am at 14.5kJ reserve. Later in the race I am storing power up to around 20kJ. The majority of the race is done within a 5kJ W’ band. These are little power bursts, 5-15 seconds with short recovery.
Now, if I were really good at dealing with the lactic acid I might get myself down to 7kJ and then manage my effort between 7kJ and 12kJ. This would give me much more time at the front, perhaps causing others to lose my wheel due to the pace.
Regardless, the Tabata protocol does a good job of putting you in a fatigued state and hardening the mind but it should be noted that you might change the protocol if your goal is to simulate a cross race. For instance, 5 intervals, followed by tempo with periodic 5sec power bursts or whatever you can do to keep you in that deeply fatigued state.
Disclaimer: I probably should have put this at the top of this post but please note that I’m not a Dr. or sports physiologist. I’m just a dude with a power meter riding my bike and trying to make sense of the numbers.