For the uninitiated Cross Country skiing, also known as Nordic skiing, has two techniques. Classic - where the skiis move in a straight line along pre-prepared parallel grooves in the snow and the basic movement resembles a slow running or bounding action (badly demonstrated by me here on the left). Freestyle - which is basically like ice skating but on skiis and takes place on a smooth loipe and is faster than classic. Both techniques use the arms to add power and hence XC skiiers have recorded some of the highest VO2 Maxes recorded - remember VO2 is a measure of the body's oxygen consumption so the skiiers use more oxygen than runners say (this also raises an interesting question about whether the limitiing factor in VO2 max development is the muscles ability to use oxygen rather then the heart/blood's ability to supply it - it would suggest that it is). And to give you a feel for the speed the men go at, the Engadin Skimarathon is won in around 1hr 20mins on good snow - so 2 minutes a kilometre or fast enough for drafting to play a part as in cycling.
In Sochi the course that has been built at the Laura centre is a tough one for several reasons. Firstly its at an altitude of just over 1400m which is just enough to feel the effectos of if you are not acclimatised. Secondly, its hilly which means athletes need more power to ski uphill and the downhills can be treacherous where speeds of 70kph are reached on narrow cross country skis which only have a front binding. And thirdly the snow has been soft which means that the skiis slide less effectively taking up more energy from the athlete and presenting a challenge for the 'waxman' who prepares the skis with the appropriate wax for the conditions.

So his rehab and why it may have made the winning difference. Unable to ski Cologna and his coach Guri Hetland were forced to get creative about how they trained. Ostensibly to maintain his aerobic fitness Cologna used a couple of techniques.
Firstly he used a sitting machine that was fixed to enable him to do upper body work to maintain aerobic fitness (above left) and then later as his rehab progressed he was able to get out on the snow on kneeling pair of skiis so that at least he could mimic the full upper body pushing action (below left).
What would turn out ot be most significant about this training is that I believe Cologna created a bigger training load on his upper body than his normal training would and therefore he got a bigger adaptation and ultimately more power. And it was this extra power that enabled him to gap the field on that final climb before the stadium despite his aerobic fitness in his legs probably still being slightly off where he would have liked it to be.
So what are the take outs for runners and other sports ? There are probably many and I just want to mention two of them:
1. A very big aerobic base can survive a lengthy period of rehab with just sufficient training to maintain it. For middle distance runners and soccer players this is particularly relevant when considering the type of training programme to follow. A big aerobic base will have you back competing at a higher level sooner.
2. A very intensive block of training on a part of your system that is relatively undertrained can pay big dividends. Why ? Because of the law of diminishing returns - When my Anaerobic Threshold is already at 3min/km and my vVO2max is 2min 45sec/km and i've done 60,000km of running getting even a 1% improvement requires a huge additional training load. However increasing my standing vertical jump by several % may be a much easier gain to make with a focused strength/power block of training. And this will convert into improved running performance without needing to increase my aerobic engine.