Pictured here is a generic graph that relates finish time to age and depicts the performance elements that will be examined in upcoming figures. The points on the graph are the mean finish times each age (predicted times for a 50k freestyle event or a 55k classic event). At the upper extremes of age, mean finish times become more variable, and this is mostly due to the fact that there were relatively few skiers over which to take means. For most ages, means for each age were calculated from hundreds, if not thousands of observations over 1999-2019. For all analyses that follow, there were at least three skiers used for each mean.
A broad-brush summary can be achieved by dividing the performance curve into a younger period and an older period. This was accomplished by using multivariate adaptive regression splines (MARS) to approximate the actual performance curve by using two linear regression lines.*
The junction of the two linear lines represents the estimate of the transition age between the two periods. As will be seen, there is a relatively long period of sustained performance that is then followed by a more marked decline starting somewhere within the ages from 49 to 69 depending on technique, gender, and proficiency. The slope of the lines estimates the effect of age on performance within the two periods.
*S. Milborrow. Derived from mda:mars by T. Hastie and R. Tibshirani. earth: Multivariate Adaptive Regression Splines, 2011. R package.
The use of multivariate adaptive regression splines (MARS) provides a nice tool for distinguishing performance of male and female skiers as they age.
Male and female classic skiers show similar performance patterns in the younger phase when males slow down by about 1 minute:13sec/yr, and females slow down by 46 sec/yr. After the transition, older skies of both genders slow down - males by 5 min:15 sec/yr and females by 4 min:48 sec/yr.
The real distinction between genders seems to be the age of transition - 61 for females and 69 for males, an eight-year difference. As will be seen in the following graphs, this trend for transition age holds across technique and proficiency level.
Note: Finish times are standardized to a 55k classical race or a 50k freestyle race.
Freestyle skiers seem to hold their speed well into middle age. There’s no discernible slowing for females until they reach their transition age of 49. Males slow at 39 seconds/year until their transition age of 57.
As with the classic technique, there was an eight-year difference in transition age between the genders. The transition ages for freestyle skiers are markedly earlier than for classic skiers - 12 years earlier for both genders.
After the transition age both females and males slow down at a similar rate of about 4 minutes/year.
Note: Finish times are standardized to a 55k classical race or a 50k freestyle race.
For the fastest three classic skiers of each age, overall performance patterns are very similar to those of the average classic skier, with the exception of the pronounced decline in performance after the transition age.
In the younger period, the top 3 classic skiers slow down at less than one minute/year - essentially the same rate as the average classic skier, and the rates are perhaps a little lower for females (46 seconds/ year) than males (59 seconds/year). The transition ages of both genders are exactly the same as those of average skiers - 61 for females and 69 for males, again an eight-year difference.
But after the transition age, the wheels really come off the cart for top 3 skiers. Performance declines at a rate of about 12 minutes/year for females and 13 minutes/year for males. It is obviously more difficult for elite classic skiers to maintain high speed into to the older period than it is for the average skier, although elite skiers are still skiing much faster than their less competitive peers.
Note: Finish times are standardized to a 55k classical race or a 50k freestyle race.
For the top three freestyle skiers of each age, patterns of performance during the younger period are similar to those of the average skier. The top 3 freestyle skiers slow down at about the same rate as the average skier, and the rate is slightly lower for females than males.
The transition ages are 57 for females and 65 for males, again an eight-year difference. The transition ages for top 3 freestyle skiers are 8 years later than the transition age for average freestyle skiers for either gender.
After the transition age, performance declines at an accelerated rate of about 8 1/2 minutes/year for females and 9 1/2 minutes/year for males. Just as with elite classic skiers, it is difficult for elite freestyle skiers to maintain performance after the transition age.
Note: Finish times are standardized to a 55k classical race or a 50k freestyle race.
In general, classic race times may have decreased somewhat over the past 19 years, while the same cannot be said of the freestyle race. From 2008 on, the classic and freestyle events had separate start waves and a separate trails to OO. So while the distances for the two races were equal to each other up to 2008, in 2008 the classic trail was about 2 km longer, and from 2009 on, about 4 km longer than the freestyle trail.
Finish times, however, in this graph are standardized to a 55k classical race and a 51k freestyle race for all years, so the convergence of the finish times for the two events probably indicates that after 2008 classic skiers were able to increase their overall pace, especially during the first half of the Birkie, because of less interference with skate skiers. The downward slope of the trend line suggests that the classic finish times have decreased at a rate of about 4 1/2 min/year.
There were several notably slow races, particularly 2001 when 8 inches of new snow fell from midnight until midmorning on race day. In 2002, the classic race was plagued by warm conditions and a badly deteriorated track. In 2014, 18 inches of snow fell in the two days before the race, and the temperature was well below zero at the start.
Note: Finish times are standardized to a 55k classical race or a 50k freestyle race.
The mean age over both genders and both techniques has not changed much, from 41 in 1999 to 44 in 2016. The mean age of men has increased fairly steadily over the years while that of women has remained steady or slightly declined in recent years.
On average, classic skiers are about 4.2 years older than freestyle skiers, and women are about 5.5 years younger than men.
Further age breakdown:
Classic - female = 41.4
Classic - male = 48.1
Freestyle - female = 38.4
Freestyle - male = 43.5
The proportion of women has increased slightly over the years. Women made up 19% and 22% of the total classic racers in 1999 and 2019 respectively. For the freestyle race, women were 15% and 19% of the total in the two years. The proportion of women totaled over both races has increased from 15% in 1999 to 20% in 2019.
The proportion of classic skiers has increased dramatically over the years, from 4% (35 females and 150 males) in 1999 to 34% (415 females and 1458 males) in 2019. The classic event became more attractive after the new classic trail was established in 2008.
The increasingly popular classic race has been responsible for the much of the significant growth in total number of Birkie skiers.
There is a steady increase in finish times from the elite wave to wave 7 for both events, with each wave finishing about 27 minutes slower than the one preceding it for classic racers and about 23 minutes slower for freestyle racers.
For waves higher than 7, many racers may be experienced skiers, but they may also be first-time Birkie skiers without finish times from qualifying events that would have placed them in one of the earlier waves.
Note: Finish times are standardized to a 55k classical race or a 51k freestyle race.
For this database, each skier's wave placement was determined by bib number although in a few instances additional steps were needed to separate elite racers from wave 1 racers. The Birkie includes several honorary waves for founders, those who have skied 35 Birkies, and those older than 70. These honorary waves were not included in this table.
1997 was the first year when the classic and freestyle racers were distinguished from one another in the results, even though they still had common start waves based on prior finish times regardless of technique. Therefore, there were relatively few classic skiers in the elite and lower number waves until 2008 when the two races had separate starting waves based on separate finish-time criteria, and the new classic trail was first used.
The current (2017) policy for assignment to the elite wave is that the top 200 male and 60 female finishers from the previous year's Birkie freestyle race, and the top 100 male and 40 female finishers from the previous year's classic race are automatically assigned a starting position in the elite waves for the current year. This policy has changed over the years, and it also seems that there have been special situations when notable skiers are allowed into the elite waves without having skied the Birkie in prior years.
The size of the first five waves of the freestyle race have remained relatively constant over the years, although it is hard to really determine this since the Kortelopet skiers are excluded from this summary.
It's readily apparent that the classic race has become more popular, especially since 2008.
How fast do we slow down (1999-2019)?
Birkie trends (1999-2019)