First, Y3T is a system invented by Neil Hill. Flex Lewis is one of the bodybuilders who uses it on a regular basis. It involves changing up the type of training you perform every single week. It is a 3 week cycle that gets repeated 3 times for a total of 9 weeks.
I found that I made strength gains while on Y3T. I believe it is because the system cycles you through various repetition ranges and that forces all muscle fibers to be engaged during a 3 week cycle.
Recovery started to become an issue as the program went on. At first I was fully recovered and ready to train by the time a body part was scheduled again for training. This because frustrating because I'd have to adjust the schedule to accommodate the fact that I was not yet recovered. I believe that the system is so intense that recovery becomes more difficult. In the long run, there are ways around this as long as you are willing to be flexible with your training schedule.
I gained size while on Y3T. My back improved as did my shoulders. There is something to be said for the approach used in this program. It has heavy days, light days and extremely high repetition days. These each stimulate growth in their own unique way. What I thought about while utilizing this training is that certain body parts on me respond to different types of training. Y3T automatically handles this by including 3 types of training over the 3 week cycle. It obviously worked well for me.
This program is very well thought out, but it involves a body part split. If you've been reading my contest preparation journals you will know that I am currently not sticking to a body part split type of training. I use my instincts and train what needs to be trained. If I were to incorporate Y3T into my training schedule again, I would skip the body part schedule and just use the workouts as outlined. I would cycle the type of training as programmed into Y3T. I think that the concepts are very helpful for the budding bodybuilder.