Most trainers typically do 3-4 sets of an exercise, but with chins Arnold commonly used a technique in which he aimed for a total number of reps—say, 50—rather than target a particular number of sets: "On the first set you may do 10 reps. Perhaps you struggle with 8 reps on the second set. You have 18 reps now. If you make 5 on the third set, you have 23 reps. You continue to add them until you've reached 50, even though it may take you 20 sets to do it. That's how I built up my chinning power, and I was very successful with it."
Several exercises from Week 1 are carried over to Week 2, but one move is added to each bodypart routine—with the exception of abs—so you can train all muscle groups more completely from multiple angles. Chest, for example, includes two exercises: One is a compound movement (dumbbell bench press) that involves multiple joints (both the shoulder and elbow) to work the largest amount of muscle possible, and the other is an isolation exercise (dumbbell flye) that involves only one joint (shoulder) and targets the pecs to a greater extent. (When doing presses for chest, the deltoids and triceps are involved to a degree, meaning presses don’t isolate the pecs as much as flyes do.)
If you've been competing for five-plus years, there is a quiet confidence that comes from knowing what you bring to the table. If it's your first time, don’t allow yourself to get rattled. Nerves cause cortisol to shoot up, which causes water retention and all kinds of other unwanted issues. If you’re well prepared and you have done all the hard work, it's time to enjoy the fruit of your labor.

Resistance training or lifting weights is a common practice in the world of people who want to get bigger and stronger. To someone who wants to lose weight, it could seem almost counterproductive to put on muscle weight when your true goal is to lose weight. The truth of the matter is that you want to lose fat, and putting on muscle can help you accomplish that goal.
The amount of exercises and sets a bodybuilder would use would vary among each individual. Some bodybuilders, like Arnold Schwarzenegger and Sergio Oliva, would do multiple exercises and sets for each muscle group to insure that the muscle was being properly trained from each angle. They would normally do up to 5 sets per exercise and 4-5 exercises for each muscle group for a total of 20-25 sets for each body part.
After session 12, consider whether you need to increase the weight for any particular exercise. If you can comfortably do more than the RM of 12 exercises, increase the weight by a modest amount, say two pounds or a kilogram for isolation exercise muscles such as triceps and biceps, and 5 pounds or 2.5.kilograms for compound and large muscle group exercises like squats and deadlifts. When using dumbbells, this would apply to each one. Don’t increase the number of sets beyond 3 at this time.