Quantifying Differences In Average Speed Between Classic/Skating

I received an email recently from a reader who pointed out to me that Marit Bjørgen completed the 30k classic mass start in Oslo this season in 1:26:09.8, last year at World Championships Therese Johaug did the same course, mass start, skating in only 1:23:45.1, which is only a difference of about 2.8%. Surely, skating is more than 2.8% faster than classic?

Now, there are all sorts of reasons why unusual differences like this could occur. Strange weather and snow conditions, obviously, is the major culprit. My memory for those things isn’t so good, but my correspondent assured me that the classic conditions for Bjørgen were not favorable, which should have made the gap much larger, one would think. (I’m also assuming that the course really is identical, which is another factor that I have very limited knowledge of, being many thousands of miles away with limited TV coverage.)

As a first pass, let’s just look at the average speeds for the winner of all recent women’s 30k mass start races:

Now we can see that the average speed difference does appear to be quite large, but that my correspondent happened to stumble across a particular pair of races that weren’t that different. But clearly I can’t stop here.

Before going any further, let me be up front that there are numerous important variables that influence average skier speed that I can’t control for simply because I don’t have the data. Weather and snow conditions, as mentioned above, but also the fact that I collapse race distances down to their “advertised” distance. For instance, if the schedule says it’s a 15km course, that’s what I call it. The PDF race results will typically have a more accurate number, but pulling data out of PDFs is just more trouble than it’s worth.

With those caveats in mind, I went ahead a fit a big complicated model. Well, it’s not really that complicated, but I’ll spare you most of the details. Basically, it models average speed among the top 30 skiers as a function of gender, technique, race type (mass start vs interval start), race length and time (to account for changes in speed between, say the mid-90’s and now). There were a little over 16,000 observations in the data set used for this model.

Then we can look at the model’s estimates for the average speed of skiers in various types of races. First, the men: Read more

Technique Specialization

There are two somewhat different ways in which you could be considered a skating or classic specialist.  First, you can be noticeably better at one technique than the other.  Second, you could just only do races of one technique or the other.

These two situations might overlap, or they might not.  In any case, they are easier to consider separately.  Let’s look first for skiers who specialize via participating primarily in one technique or the other.  Some ground rules: I’m going to toss skiers with fewer than 30 WC, OWG or WSC races in their career, pursuits with a break will count as one classic race and one skate race, pursuits without a break will count as half of classic race and half of a skate race.

We could get picky about changes over time, particularly with changes in the number of classic/skate races available on the schedule each season, but I’m going to ignore that for now.  Also, keep in mind that there will be skiers here who’s careers extend beyond my database, so the data for them is incomplete.  Requiring at least 30 races weeds out the more extreme examples of this, but not all.

First let’s look at the distribution of the percentage of skate and classic races by athlete for their entire career: Read more