great question!
while normally Iwould tell someone to mix up changing all 3 variables (increase work period, decrease rest period, increase # of intervals), I wouldnt increase the work interval past 1 minute. 1 minute is probably the max I would suggest, because the work isnt really maximal anymore (even though you are in OMG mode)
First thing, shorten the rest interval to make it a 1:1 work to rest.
Then, after a month or so of that, go back to 15-45 seconds at 100%+of MHR, maybe on a different piece of equipment, recovery period as needed, and add more intervals.
Excellent answer Gymcoch, thanks so much for your help!!!
Today I switched to 1:1 and after 15 mins I really felt the difference
One more question do you think HIIT can have the exactly same results if I do it after weight trainning (1 hour really hard) as if I do it first thing in the morning????
there is actually research supporting shorter intervals to be better, something like 15 to 30 seconds. personally i believe in mixing it up so your body doesnt adapt.