I think more than heart rate, you should also look at how they felt. Did the 30/30s get you to that gasping for air/fish out of water sensation? That seems to be one of the greatest indicators that you are at VO2max. Also, maybe consider that the 1:1 work:rest ratio is too low and maybe consider 45/15s or something like that if you want to keep going to short/short route.
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