What are you trying to achieve with those different tasks? Sub maximal effort exercise for extended periods of time will improve cardio and endurance. To show large gains you probably need to do this 3 times per week. Doing HIT will have a small benefit in weight loss but most people that say they do HIT really don’t do it. If you can maintain that intensity for longer than about 30 seconds it wasn’t HIT. If you don’t feel physically ill after the 30 second burst then it wasn’t HIT. Not sure HIT will increase muscle mass that much? If you want to build muscle mass then you need to do resistance training, weights etc. If you want to lose weight then its mostly diet related, HIT will have a small impact on weight loss. So as fitnfast has said pick your goal.

Weight loss = diet
cardio = endurance training
muscle mass = resistance training

There are actually a lot of different forms of HIIT. What I did in cross country training in high school would probably kill me now! At the time it was common for one or two to even throw up during the interval workouts. Typically we had to 6 to 10 cycles and we had to run at set paces that were painfully fast. Typically 10 cycles of either quarter mile or half mile. The rest was just until our heartrate hit a certain threshold, and it was always way too short for comfort. After the last cycle you might just lay on the ground for 10 minutes before getting up to slowly go back to the locker room and clean up. There wasn’t any talking after those workouts. That was decades ago.

Five years ago I started with Tabata style. Basically 20 seconds hard, rest 10, repeat 4 times for one set. Can be the same or different exercises. I did different because I was out of shape. It was effective but as I got into shape I fell into old cardio habits and did a lot of running.

Over time I learned a lot of bodyweight exercises. If you want to feel what a painful death could be like, do HIIT workout with mountain climbers. That is if you are pushing to the max.

I’ve been doing Sprint 8 style because I’ve reach a point where the first two hard intervals don’t tax me enough. Typically it isn’t until there 3rd one that I feel like is going to kill me. Ideally I want to see my heart rate hitting around 170 and then in the rest period going to the 120’s. The recovery cycle is just as important as the sprinting.

Currently I use a 30s hard 90s recovery cycle and I repeat that 8 times. Early on I typically start early because my recovery is fast. By number 7 I typically can’t recover in 90 seconds. Also if you can talk after the sprint you aren’t breathing hard enough. Typically by #3 I’m at that level. I don’t think there is anything that special about 30s. It is just pushing yourself too exhaustion, whatever it takes.