Wednesday, October 3, 2012

Bridge-to-Bridge Run 2012: pacing analysis

A nice thing about running with GPS is the ability to go back afterwards and try to analyze what happened. Did I go out too hard or too easy? Was there a particular section of the course where I had special difficulty?

First, results. I finished in 41:46, 33rd overall out of 1653, 32rd overall out of 727 males. I can't complain about that. But I need to remember a large number of the runners were just out there to enjoy the day and the views, not shaving seconds.

In cycling a power meter is really nice for pace analysis, but in running we only have pace and road grade. These are usually fairly good because running pace isn't as dependent on external conditions such as wind and surface quality as is cycling, but even a few % difference in speed-at-a-given-effort can confound trends in effort due to fatigue or loss of focus.

On Bridge to Bridge of the more than 1600 runners, 20 others are listed on Strava as having done the run with me. To get a match, they need to have run a sufficiently similar pace that Strava recognizes us has having been together. Additionally, of course, the runner would have needed to record their run on a phone or GPS unit, and to have uploaded it to Strava. Their market share around here is less in running then in cycling, but it's growing.

I stumbled upon one runner in particular who seemed to be suitable for comparison: Philippe Le Rohellec of San Francisco. A quick glance at his Strava record shows he mixes cycling and running. He finished the Bridge to Bridge in 39:56, right at my reach target.

First, temperature: my Garmin reported between 18 and 22 C during the run. However, it was mounted to my wrist and obviously there it's exposed to body heat. So this places an upper bound on the ambient temperature.

Next, I'll look at speed. My target was 10 kph, as I've noted. In the following, I smooth the speed with respect to distance with a characteristic length of 50 meters, so peaks and valleys will be underestimated, but "noise" due to GPS error will be reduced.

speed

You can see I start out above pace, then settle into my 15 kph target, then there's the hiccup from Fort Mason, then I sag a bit before partially recovering in the final kilometer. In contrast, Phillippe had a very strong middle race, actually picking up his initial pace.

Of particular interest was Fort Mason. I zoom into that here:

speed

I curiously had two sags in speed leading into the climb. I think the first may have been distraction from the aid station which I skipped, or perhaps the view of the upcoming hill. I'm not sure. Phillippe had no such issues.

Then we hit the main climb. Phillippe was substantially faster on the early portion. I recovered quicker over the top, perhaps having paced myself a bit more conservatively on the steep climb. On the descent I was actually okay in comparison to him, but then once we hit the flats he kept his speed, while I soon dropped below my 15 kph target, never again to recover it.

gap

I can also compare our relative positions. Here I take, for every Phillippe position, how far back I was. The most interesting aspect of this plot is its simplicity: I held him close for 2.5 km, then he started to pull away at a steady pace for the rest of the way.

So what held me back from my 40-minute reach goal? The answer, it seems, is I ran too slowly. You could say I started out too quickly, but I started out at almost exactly the same pace Phillippe ran. Rather, I simply couldn't make it happen after the first 2.5 km. I didn't really crash: once I slowed relative to Phillippe I was able to hold that speed differential.

I shouldn't give up hope. My friend from the start line, who I now see was Tim McMenomey, finished the Avenue of the Giants 10 km race (results) in 38:33 on May 6th, yet he finished only two slots ahead of me here, in 41:22. So differences race-to-race of several minutes may not be unusual, although I've been remarkably more consistent in my spotty but long-in-time 10 km running career.

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