training intensity involves “down time” when no effort is made to produce new gains in muscular size and strength. There is some detraining because, by cutting back, you get a little weaker than your previous best, before pushing again to go into new (for you) poundage territory.
Taken to its extreme, i.e., if you cut back too much and for too long, cycling is a disaster. Do not abuse cycling. A 6-month “perfectly” organized stretch that brings you to a peak for just two new-ground workouts is a perversion of cycling. You need to train very hard for a darn sight more than a few weeks out of every 26 - for most of your workouts, in fact.
Some people see intensity cycling as a waste of time because they think that the more hard workouts they have, the better. They are so eager to get training flat-out, or very near to it, that they never develop the gaining momentum needed for long-term progress. Also, by dropping right into full-bore work, how are exercise form and mental concentration going to be learned or reviewed, and then perfected?
While you should push yourself to the limit for most of your workouts, “most” does not mean “all.” Learn not to push yourself to the limit during some periods. This is difficult to do if you have been locked into the “hard all the time” philosophy. Those who try to train full-bore all of the time have a built-in natural cycling format, whether they like it or not. Is there any typical working and family person who can train full-bore two or three times each week for 52 weeks of the year while being 100% healthy, 100% motivated for every single session, and not having work or family circumstances disrupt training? The disruptions and constraints of life force people to have ups and downs in their training, giving it a natural cycling format.