Sunday, March 22, 2009

Tale of Two Fridays

Friday's Noon Ride seemed fast to me. The nice thing about power data is they allow one to put a quantitative validation on such qualitative assessments. One of my favorite ways of looking at ride data are maximal power curves. These are the maximum average power recorded during the ride over intervals of various duration. Here I compare average powers over four rides: three noon rides and the Menlo Park Grand Prix criterium, for durations from 0.05 minutes (3 seconds) up to an hour:

maximal power curves
Maximal power curves for two Friday Noon Rides, a Thursday Noon Ride, and the Menlo Park Grand Prix. FTP estimated from the Menlo Park Grand Prix normalized power is also shown, along with a curve using the Critical Power model for AWC/CP = 40 seconds with this FTP value.

On the plot, I point out a key feature of that Thursday ride: the hard effort of the Canadã College loop, which is a pair of climbs separated by the descent. Note the peak average power increases with increasing time for a bit here. This is a characteristic feature of two hard efforts separated by a brief recovery.

I also "sketch in" a "theoretical maximum" curve generated with the elegantly simple Critical Power model. This model assumes there is a fixed "Anaerobic Work Capacity" (AWC) which can be spent over a certain interval of time, then is slowly regenerated. The ratio of AWC to Critical Power (CP) is units of time. It takes a certain minimum amount of time to utilize AWC, so I sketch the curve only for times of one minute and higher. The effort of Canada College fails to reach this curve, because the curve can only be reached for efforts of approximately constant power, while the Canadã College interval was far from constant power. The same is true of Menlo Park, which had hard accelerations separated by drafting and braking (way too much braking due to my poor pack position).

The comparison of interest here is the two Friday Noon Rides. For each power interval, I worked harder during this week's Noon Ride than the one in February. Warm weather, later in the season, and folks are feeling friskier. I put in a little attack myself, just to make life harder on myself.

P.S. Nice discussion here of the Roaster Ride Sting last weekend. What a total joke. My money is on these tickets getting tossed out upon challenge.

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