Split your training into relatively small intervals where you can push yourself to the limit. The breaks in between allow you just to recover enough for the next interval.
Instead of running 45minutes on a treadmill at 10km/h you could better apply the following HIIT:
1) 3 minutes warmup on the treadmill at 7km/h
2) 6 intervals of 45 seconds at 14km/h sprint followed by 40 seconds break each. You can of course run at fast as you can.
3) You can then finish the workout with a 3minutes cool-down phase at 5km/h.
You have then trained for less than 15minutes, and nevertheless you have pushed yourself pretty hard. You can vary the intervals by making them longer or you can shorten the breaks. You can also run faster. The goal is to be exhausted after each interval.
You can apply HIIT on any kind of trainings i.e weight training or abs workout.
Enjoy you HIIT Time.