The ultimate Lausarunner question: which race is harder, the 20K or the Half Marathon?

A data analysis to answer this fundamental question

I found myself asking this question after running the 20 Kilometers of Lausanne last April. For the ones living elsewhere, there are two main races of this distance in Lausanne: the 20K in April and the Half Marathon in October. The BIG difference, besides 1.2 km, is that the Half Marathon is rather flat along the lake (110m up and down according to my watch), and the 20K goes uphill to the cathedral and down again (270m up and down according to my watch). Most people believe the 20K is the harder race.

I am trying to get back in shape after some progeny production last year. And suddenly, I ran the 20K in an awesome (by my standards) time of 1h34, faster than my fastest Lausanne Half Marathon ever (1h37). WHAT? No way!! I am not fitter than I was before! Is the 20K not that hard after all?

Rule of thumb calculation: both races are equal in effort

If we apply the rules of thumb: (i) 100m uphill = 1km flat, and (ii) downhill compensates for half of the uphill, we end up with two roughly equal races. The Half Marathon is further in distance, but you ascend more in the 20K so at the end it equals out. We would expect people doing similar times in both.

Ok, that was still fine for me! Super coool! With my 1h34, this meant I was better than “just” back in shape!

But let’s look at the real data…

In reality: people need more time to run the Half Marathon

For these two races, all results are online in Datasport, so I checked the validity of the rule-of-thumb in our situation. Result: nope, people don’t do similar times in both, people need more time to run the Half Marathon!

Finishing times of all participants from 2013 to 2016 (34’520 participants in total). Vertical lines indicate the median race time.

The median 20K runner did 1h41 and the median Half Marathon runner did 1h54. That’s 13 minutes longer! The 20K is definitely easier! This time difference is more than “just” running for 1.2km longer — this time difference means the median Half Marathon runner is running at a slower pace:

Running pace of all participants from 2013 to 2016. Vertical lines indicate the median pace in min/km.

Could it be that the average runner of the 20K is fitter than the average runner of the Half Marathon?

Ok, it could be that the 20K is tougher, and the average 20K runner is also tougher :). Age distribution was basically the same in both runs (although Xavi showed that actually the age doesn’t matter that much). However, there was a higher proportion of women running the Half Marathon than the 20K.

Age distribution of participants from 2013 to 2016 (left) and their genders (right) in both races.

This actually could make a difference, but even when we separate men and women, both genders run the 20K at a faster pace. So no, the slower median pace for the Half Marathon is not due to a higher proportion of women.

Running pace of all participants by gender and by age. Boxplots limits = interquartile range, whiskers = 5th-95th percentiles. Those little red dots are me!

People running both races in the same year keep the same pace

The fact that more women run the Half Marathon indicates that the profile of the runner is different between the races so perhaps they are not comparable. What about people that run both races in the same year? Over the 4 years between 2013 and 2016 I got around 2400 of such brave people, and they run a median of 3 seconds/km slower in the Half Marathon.

Pace difference between Half Marathon and 20K for people running both races in the same year (between 2013 and 2016).

Most people take longer to run the Half Marathon than the 20K. It seems that the super tough uphill of the 20K is actually not much worse than running flat :)!

Time difference between Half Marathon and 20K for people running both races in the same year (between 2013 and 2016).

To sum up: I am not fitter (not cool)

Counter-intuitively, the median runner manages to keep the same average pace in the 20K (with its feared cathedral climb) as in the Half Marathon (flat easy-peasy along the lake). The Half Marathon is therefore “harder” (in the sense that the same person takes longer to finish it). I don’t know why. People might be fitter in April? People train more for the 20K?

  • More “slower runners” run the Half Marathon. Probably something to do with the (apparently wrong) perception that the 20K are harder?
  • My pace in the 20K was 4’44’’ and in my best Half Marathon I did 4’37’’. So I am not fitter than before.

I should have left it at the rule of thumb stage…