If you are new to Zwift, and especially if you have never met before with your power numbers only until your newly purchased smart indoor trainer, then first thing you will have to do before entering into any Zwift event like Slovenian Winter league, is to find out what your actual abilities are and what category you fit in.
One of the best Zwift “social” features is the possibility to join riders into smaller groups with similar abilities. Unfortunately (or fortunately) we are not all the same. The bitter truth is mother nature has created extremely wide differences among individuals. Not only everyone haven’t got brown eyes, dark skin, small nose, long and skinny legs, etc.. same applies to our cycling abilities. Some are tiny and can metabolize the huge amounts of oxygen aerobically, say perfectly built for fast climbing, others might be largely built, a bit overweight and without a lot of sporting background from youth, thus unable to follow much faster, stronger, leaner athletes. The range of abilities is really large. But, with choosing the right category you can be joined to people within a fairly similar group. In this case, even women can fairly equally compete with men and even override them.
Slovenian Zwift league uses most common 
group division format on Zwift and on Zwiftpower, and its based on individual abilities expressed in Watts per kg (W/kg)
FTP above 4.0 W/kg FTP 3.2 to 4.0 W/kg FTP 2.5 to 3.2 W/kg FTP under 2.5 W/kg
But wait a moment, what the heck is FTP?
If you never met with the term FTP yet, then you really are new to power-based cycling. Arguably, it’s the most common term used among spirited power-meter users. It’s a simple abbreviation for “Functional Threshold Power -> FTP”. In practice, your FTP is roughly equal to the maximum power you can hold for one hour. Simple as that! But in theory..o my, damn theory. it’s something almost illusionary. Want to know more about the theory of thresholds surrounding common FTP? Then read this beautiful article on Pulse Performance about the entire ecosystem of thresholds and their relation to each other (in Slovenian language only).
How to estimate your FTP on Zwift?
Since all the results from any Zwift event, from group rides, workouts to races are stored on Zwiftpower and our league demands having created Zwiftpower profile, we choose to use the most simple estimation of FTP possible. That is, 95% of your maximal 20-minute power output. Phenotype up, phenotype down, it’s the same marker Zwiftpower uses to delimit between groups.
Estimating is as easy and simple as it gets. Go on your trainer, run Zwift, warm up for 15-20min and then simply put the hammer down for exactly 20min. No mercy. All-f***ng-out. Once finished, check your 20min power, reduce it by 5%, divide with your weight and voila -> it’s your FTP estimate.
Example: Luka Zvonec weights 83 kg and has averaged 307 W over 20 min test.
(307 W * 0.95) / 83 kg => 3.5 w/kg.
His FTP is around 3.5w/kg so he chooses to participate in Category (FTP 3.2 to 4.0 W/kg)
For any newcomer to Zwift, it’s by far easiest to simply do the FTP test within the Zwift itself. Anyone can find it among preloaded workouts in the app. Just run it and follow the instructions.
What if I am right on the category border and do cross it?
This is a common scenario, especially among beginner cyclists. The category borders have to be set somewhere and there will always be somebody who’s ability is right on the limit. In this case, if it’s about experienced Zwifter, we recommend choosing a higher, stronger category. Because if it happens to someone to cross the limit with 95% of maximal 20-minute performance, he or she will get a strike. A maximum of two strikes is allowed within 9 week-long series. On the third strike, a rider has to be upgraded to the upper category and his points in general classification get reset to zero so he starts from there, which can be quite a bummer.
For beginner cyclists, this might be more common since they might improve very quickly during several weeks of the league. In this case, they should not take it as trouble, but be happy about it. Ultimately it’s a good sign of their performance improvement.