I have often been asked the question ‘What does 3 x (3+3) minutes VO2 max mean?´ so I thought it would be a good idea to spent a short post on it. 3x(3+3)min VO2 max means 3 times 3 minutes maximal effort with recovery periods of 3 minutes between each interval. (3min hard work, 3min recovery, 3min hard work etc.)
VO2 max refers to the intensity you shall try to maintain through the intervals.
It’s clear that you don’t know what your actual VO2 is, but when you have tried these intervals a couple of times you will know how to pace yourself.
The important thing to remember is that you are supposed to ride as fast as you can for a period of 3 minutes (but not faster than you can repeat it a couple of times).
It is not possible to use a heart rate monitor for pacing because of the delay of the heart rate but can be a good indicator of your performance afterwards.
A power meter like SRM or PowerTap is very useful for such pacing. Yeah, they are expensive, but strongly recommended if you are a serious cyclist.
In the recovery periods it is a good idea to do some light pedalling to remove metabolites. That will make it easier for you to make the following interval at the right intensity.