You maybe start college soon and you  don’t want to be the smallest guy there. you  probably 5’11 and I weigh on average 165 lbs. You may was doing P90X but multiple sites and forums explained that it was a program mainly for toning and losing weight. you will stopped now before you disappointed yourself.

So now you just want to get the ideal for muscle. You get it  that working out the whole body is ideal but you really eager to increase my arm and neck sizes.  You must really want to know what are the best exercises and P90x Workouts Schedules you should follow.

You may ask some questions as:
1. How many times should I do cardio & abs and could you still use P90X for those workouts,  eating a lot so which foods should I aim for or decrease, usually wear a 20lb weight vest doing P90X so how can I incorporate that in the muscle growth program, really?
2.  I take one-a-day multivitamins should they be good after my workouts?

The diet – first you need to find out how many calories you need to be eating to maintain your current weight, then you add 500 calories to that amount. Eat lean, and try to get 1 gram of protein per pound of body weight. Keep your fat at 20% of your total calories. Supplement with a whey isolate drink post-workout. Take it within an hour after your workout. Supplement with ~25 – 40 grams of the whey isolate.

Hope this helps: Eat quite a bit of red meat. Try to eat mostly red meats like steak, drink lots of milk and water, and work out in the mornings. If you are a veggie person than eat those a lot too. They will help you gain muscle faster If these things can raise your metabolism. Decrease fatty foods like candy, chocolate, honey buns, etc. and try running before you do your P90X workout. Try doing lots of pull ups and whenever you do arm exercises try to use at least 16-25 pound weights.
FYI: There are 5 calories per gram of carbohydrates and protein and there are 9 calories per gram of fat. So, you want 162 grams (659calories) of protein, 19% fat calories of whatever your caloric intake should be and the rest should be carbohydrates.

The workout – you want to keep your repetitions between 8 and 13 (68% – 78% of your 1 repetition max). You want to do 3 to 4 sets. When you get to your last repetition, you want to be at failure. If you feel like you can do more reps, then you need to increase your weight. You want to do a minimum of 8 reps and a max of 14. Rest about 2 to 3 minutes between sets.

Do cardio 3 to 4 days per week for about 35 minutes above. I recommend HIIT (high intensity interval training) training. Long endurance type cardio, like running, will interfere with muscle gains.

I would recommend seeking the help of a good personal trainer and a p90x workout blog to learn it more.