1) Can I do this program in season?
Yes! The biggest factor we want athletes to be aware of, while doing this program in-season, is "Over-Training". Over-training can increase the physical stress on specific parts of the musculoskeletal system, and increases the risk of injury. Some symptoms of over-training include (are not limited to): Increased rate of illness or susceptibility to illness, persistent muscle soreness, elevated resting heart rate, loss of motivation, insomnia, increased instance of injury, and loss of appetite. In other words; taking on "more" does not mean you will get "more" out of the program. It often means you will get less out of it. If you ever start to feel like you are taking on too much training, back off of either the program, or whatever other fitness related training you might be doing on top of the program (Basketball Practice etc. NOT included in this).
2) How important is my diet?
Food is fuel. A car won't run without fuel. A car won't run efficiently with the wrong type of fuel/oil. If we want to have a powerful body (vehicle) we need to fuel it properly. It's important to fuel for your day, and fuel for your training. In other words, we need to make sure we are eating enough to fuel our workouts. Diet is very important to your success as an athlete. When we learn how to fuel our bodies efficiently, we are capable of breaking through new barriers and really opening ourselves up to our true athletic potential.
3) How do I maintain my gains?
The best way to maintain gains is to repeat the Week 8 program.
4) How important is the diet?
If you look at any great jumper - they have really ripped bodies (there are exceptions of course). But if you want to jump higher you need to lose fat and increase muscle. Moreover, you need to recover and build your muscles in between every workout session - diet helps you do that. And lastly, you need to have energy when you work. Diet is responsible for all of this; so yes, it is very, very vital to your success in the program.