Sunday, February 15, 2009

Riding with Power

I've had a CycleOps PowerTap for about 15 months now.  The device was immediately useful to me in a few ways:

  • I went out and did my own 5-minute, 20-minute and 60-minute "tests" to establish training zones and benchmarks
  • I became more aware of those subtle surges in power, when you don't realize just how hard you are working
  • I measured some of my hard efforts in bike races to figure out what it takes to get away (and hopefully stay away) from the group
  • The new toy gave me one more reason to get out and ride!

But I get even more value out of the device now that I have a coach planning my bike workouts and prescribing & analyzing blood lactate tests.  There are some great books out there to help with the workout side (I recommend Training and Racing with a Power Meter by Hunter Allen and Andrew Coggan and Coggan's Power Profiling article on the TrainingPeaks website) but I recently learned something cool on the testing side of things.

I'd always thought that the point of blood lactate testing was to find your lactate threshold, which the geeks among us know to be a better predictor of triathlon racing performance than VO2 Max.  But you can get another very interesting number from your test, what I'll call the Z1/Z2 boundary.  Check out this picture:


At low intensities, your blood lactate concentration may fluctuate a little but it is basically flat (the blue region above).  At some critical point, your lactate starts increasing linearly (yellow region).  At the highest intensities your lactate concentration will increase curvilinearly (red region).  You've probably guessed by now that the first transition is this Z1/Z2 boundary and the second is the Lactate Threshold.

At my first test, my coach noticed that my Z1/Z2 boundary was significantly lower than it should have been for a rider with my lactate threshold.  This caused us to focus a bit more on lower intensity riding, as well as core strength and pedaling efficiency.  I know other gifted racers with the same issue -- we have the capacity to work very hard and we use this to compensate for our pitiful Z1/Z2 boundaries.  After three months of focused training, my Z1/Z2 boundary wattage has increased by 30W and my lactate threshold power has also increased by 30W while doing barely any high-intensity training.

The notion of zones 1 & 2 as "fat burning zones" is a bit misleading.  You don't stop burning fat when you work harder.  You start adding "energy from carbohydrate metabolism" to that maximum output derived from fat.  Looking at the output side, if you can generate more power from just fat (via improved fitness and/or efficiency) then this gain will translate directly over to higher-intensity riding.


So if you can increase the height of that yellow box then you get to use that increase in power at any workload.  The same is true for the height of that blue box -- raising your power at LT will help you in shorter efforts like jumps and bridges in bike racing.  The green area above is another favorite topic of mine ... but a topic for another post.

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