General Max VO2 intervals are race pace intervals and work the cardiovascular system using a non ski specific mode (i.e. running, biking, swimming, etc).
Progressively work into the intervals until you hit your desired pace at the 30 sec mark. Make sure you are not starting them all out.
Specific Max VO2 intervals are race pace intervals and work the cardiovascular system using skiing or activities that simulate skiing very closely (i.e. classic/skate rollerskiing, bounding with poles, classic/skate on snow skiing).