I know there are many HIIT programs but I certainly would not call 2*20 or something HIIT. HIIT training are highly anaerobic short intervals, usually at least 6 or 7 of them with very short rest and not lasting longer than 2 minutes each.
2*20 I would call conventional intervall training.
definition of HIIT at wiki:
http://en.wikipedia.org/wiki/High-intensity_interval_training
"High-intensity interval training (HIIT), also called High-Intensity Intermittent Exercise (HIIE) or sprint interval training, is an enhanced form of interval training, an exercise strategy alternating periods of short intense anaerobic exercise with less-intense recovery periods. HIIT is a form of cardiovascular exercise. Usual HIIT sessions may vary from 9–20 minutes..."
not any interval training is HIIT.
2*20 I would call conventional intervall training.
definition of HIIT at wiki:
http://en.wikipedia.org/wiki/High-intensity_interval_training
"High-intensity interval training (HIIT), also called High-Intensity Intermittent Exercise (HIIE) or sprint interval training, is an enhanced form of interval training, an exercise strategy alternating periods of short intense anaerobic exercise with less-intense recovery periods. HIIT is a form of cardiovascular exercise. Usual HIIT sessions may vary from 9–20 minutes..."
not any interval training is HIIT.