Exercise and Fitness

All interval training is high intensity. The idea is to get your heart rate almost as high as it will go for a short duration, switch to low intensity to recover your heart rate to a lower level, then repeat a few times. Once you get in really good shape your recovery times are faster and you can do several sets in 30 minutes or so. Unless you really need the motivation, I'm not sure trying to do it within a group is all that great because other people are going to have different recovery rates depending on their fitness level. So if they base the recovery rate on the slowest person, the most fit are going to waste a lot of time. If they base it on the most fit, those at the bottom end aren't going to get the most benefit.