HIIT

I'm experimenting with this. So far I've tried three workouts:

Day One:
Warm up at 2.5-3.5 mph
20 minutes of HIIT run at 7 mph for a minute, walk at 3.5mph for 2 min
The highest sprint was 8.5mph for me!
Cooldown 5 minutes

Quite tiring

Day Two:
Warm up: 5 minutes
20 minutes of HIIT at 3.5mph this time altering the incline/grade on the treadmill. Highest Grade was 9%
Cooldown 5 minutes

Fun variation- the high incline moments were definitely anaerobic

Day Three
Warm up: 5 minutes
20 minutes of HIIT alternating between incline & speed intervals. Highest speed was 9mph, highest incline was 15%
Cooldown 5 minutes

Definitely fun. My body didn't know what to expect. My interval times in all cases can be spontaneous based on my body's needs at any given moment.

I'll see how this goes!