the longer you extend the interval time, the less intense the exercise becomes. 1:2 work to rest ratio is pretty good. 1min. tempos are good, as are less (30sec ro 20sec of work). As you get more conditioned, try and lower the rest interval instead of increasing the work interval...so maybe 1:1 and then 1:.5 (for every one unit of work you do half a unit of rest).