I try and do my HIIT (running) with 30 seconds walk, followed by 30 seconds sprint but I find this almost impossible to complete the whole session. should I try start lengthing my walk periods to maybe 1 minute folowed by 30 seconds sprints?
I use to HIIT with 90/30 or 80/40. I think the difference between the numbers is a reference of aerobic/anaerobic condition.
You could try with 90/30 and as soon as you improve your resistance you could do the numbers more similar to 30/30