Birkebeinerrennet (lit. The Birkebeiner race) is a long-distance cross-country ski marathon held annually in Norway. It debuted in 1932 and has been a part of Worldloppet as long as Worldloppet has been around.
Researchers at the Manchester Metropolitan University found that the metabolic cost for modern ski models is about 2.5 J/kg*m as compared to about 5 J/kg*m for ski models dated 542 AD. They also estimated maximum cross country speed for the 542 AD ski to 5 m/s, compared to about 12 m/s for modern cross country skis; for long distance skiing (several hours) results were 3 and 7 m/s respectively. This corresponds to about 5 hours for the original 1206 AD Birkebeiner flight.
The Birkebeinerrennet run has been held since 1932, and commemorates a trip made by the Birkebeiner loyalists to save the infant pretender to the Norwegian throne, Håkon Håkonsson, in 1206. All participants carry a backpack weighing at least 3.5 kg, symbolizing the weight of the then-one-year-old king. Till 1991 the start city was 1 year Lillehamer (finish Rena)and then the next year Rena (finish Lillehamer). Last year  In Lillehamer the start was on the site where the now the skijumparea is build for the winter Olympics 1994.
In 2007, the race was cancelled due to extremely high winds (90 km/h or 55 mph). However, at the time of cancellation, the event had been under way for nearly an hour, with roughly a quarter of the 13,000 competitors already on course. Despite the efforts of officials to send everyone back to the starting point, 55 competitors eventually reached the finish in Lillehammer, and upon being interviewed, blasted the decision to cancel the event .
The race has also been cancelled in 2014 15 minutes before the start also due to high winds of 15 m/s . Despite the cancellation, thousands of skiers completed the route from Rena to Lillehammer (and from Lillehammer to Rena) and criticized the decision  . The organizers also decided not to give any refunds, which caused an investigation by the Norwegian Skiing Federation.
Course record in bold.
Special 2002 FIS World-Cup Race
In 2002, the race was included as the last event in the FIS world-cup. The world-cup class was won by Thomas Alsgaard and Anita Moen Guidon finishing in 2:24:08.7 and 2:43:39.1, respectively, faster than both Rezac's and Hilde GP's records as of 2008. The participants in the world-cup class were, however, not required to carry the 3.5 kg backpack.
- "Birkebeinerrennet". Worldloppet. Retrieved 4 March 2015.
- Formenti, Federico et al. (2005): Human locomotion on snow: Determinants of economy and speed of skiing across the ages Archived March 4, 2016, at the Wayback Machine., Proceedings of the Royal Society B, vol. 272 no. 1572, 1561-1569 .
- "Archived copy". Archived from the original on 2011-01-23. Retrieved 2011-03-19.
- FIS-Ski Results Lillehammer 2002, Men[permanent dead link]
- FIS-Ski Results Lillehammer 2002, Woman[permanent dead link]
Media related to Birkebeinerrennet at Wikimedia Commons