I've been doing something similar to this for about 3 months now and I've seen a vast improvement in cardio fitness so I've recently upped the routine a bit.
I eat breakfast then about an hour later I hit the gym I do strength training first, down a protein shake and then do cardio. I use the stationary bike, I'm not sure what the level goes up to but by level 10 it feels like I'm trying to turn lead weights. I go for 20 mins, warm up for 2 mins then sprint for 1 min followed by 2 mins active rest upping the intensity with each sprint period and a 5 min cooldown afterwards.
0-2 mins slowly warm up to level 5, 80-ish rpm
3-4 level 6, 100 rpm (sprint) for one minute
4-6, level 6 80 rpm (active rest) 2mins
7-8, level 7 100 rpm (sprint) for one minute
8-10, level 7 (active rest) 80 rpm 2 mins
Then it starts getting difficult so active rest drops to around 75rpm and sprint drops to 95 rpm
10-11 level 8 sprint 1min
11-13 level 8 active rest 2mins
13-14 level 9 sprint 1 min
14 16 level 9 active rest 2 mins
16-17 level 10 sprint 1 min
17-18 level 10 active rest 2 min
18-20 go all out for 2 mins, 100rpm for as long as I can keep it up
20-25 cool down
The bike automatically drops the level during the cool down but when it drops below 3 I have to keep putting it back up otherwise legs go like the clappers
. By the end of that legs feel like jelly and t-shirt is drenched but once I've recovered I feel great for the rest for the day. Its taken me a while to get to this stage and I hope I can move it up to 1 min sprint 1 minute rest sometime in the near future but we'll see, heart rate already scares me doing this workout! If I can give you one tip from personal experience for HIIT workouts its this:
Don't forget to have a BIG bottle of water with you, if you're doing HIIT you'll sweat buckets!