Q: During interval recovery period should I target a specific time or a specific heart rate for a specific amount of time?
A: There are two general methods, time based recovery and heart rate based recovery. Every intensity session should have this listed. The only exception is specific strength workouts, which I would recover fully between each set, meaning that my heart rate has returned to Level 1.
Something that is also important to mention is that all recovery should be “active recovery”, meaning that after finishing an interval, you do not stand around waiting for the next interval. Easy skiing or running at a Level 1 pace should do the trick. This will actually lessen the stress of transitioning from stopped to full speed. It’s similar to keeping the engine running in a car before “flooring it”.