The Wingate test is 30 seconds long and if you want to see Max Anaerobic Capacity you will need to use a similar length test. Tests as short as 10 seconds will barely get the glycolytic metabolism activated. At rest you’ll have about 6 seconds worth of stored ATP and CP in the muscles. BTW: Your myoglobin will also have enough oxygen stored to support aerobic metabolism for a few seconds (irrelevant in this test though).
So your sprint test needs to be long enough to deplete the stored ATP and CP. But not so long as to give the aerobic metabolism a chance to get cranked up and producing ATP. Thus the 30 second Wingate test.
The cycle test is used for its simplicity and measurability. Careful work/power measurement on an ergometer will provide the total anaerobic work capacity (ie. Anaerobic Capacity). Without the ability to measure work output all you will get is the lactate number (which will probably peak somewhere between 2-6 minutes post test, depending on the anaerobic capacity and muscle fiber composition so don’t expect to see the highest lactate number immediately at the end of the test).
Anaerobic capacity is hard to train and to change. Strong FT fiber sprinter type athletes will have higher AnC than ST long distance types. It takes months of consistent AnC type training to effect much of a change. Strength plays a big role in AnC. You need to be strong and well coordinated in the sport specific movements in oder to produce a lot of power. The bike ergometer is used because most people can ride a bike and the machine dictates the range of motion so levels the playing field somewhat. But runners, unfamiliar with standing sprints on a bike will still not produce great peak AnC numbers due to the lack of specific training.
If you are trying to do this on XC skis then it is even harder because you have to be technically proficient at very fast, high power skiing if you hope to max lactate production. Training this type of max effort/speed skiing is also a long process. If your technique limits you at high power outputs then you will not get an accurate picture of AnC.
As you can see, doing what you are trying to do is fraught with challenges. Bear in mind too that AnC plays a tiny role in XC skiing, even among World Cup Sprinters. The Aerobic system so dominates not only the production of energy (even for a 3min sprint) but also for the recovery from max and near max repeated efforts in races and between sprint heats that even WC skiers spend less that 1% of their training time doing AnC building training.
There is a systematic way to build AnC for any sport: Start with developing high general strength. Move then to high specific strength, convert that specific strength in to specific power. For skiers we use weights for the general and specific strength phases, hill bounding or double poling for the power. BUT and this is the critical part: Power is not the end goal! Speed is. I have coached some very powerful but relatively slow skiers and also some relatively low power very fast skiers. WHY? Economy. So you have to train speed to ensure that power is making you faster. Medals are given to the fastest skiers not the most powerful ones.