Either – short intervals followed by the same recovery to period to get you going with it – ie 30 seconds on, 30 seconds recovery – repeated 3 -5 times during a workout, once a week. As you progress, increase the interval and shorten the recovery and increase the frequency.
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Or; pyramid intervals, so 10 on, 10 off, 20 on 20 off, 30 on, 30 off, then down again, ie 20, 10.
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Good luck, get used to the sick taste in the back of your mouth, that way you’ll know you are doing it right without a HRM or Powermeter.