Mesomorphs are the athletes who usually have no problem putting on mass. They have broader shoulders that helps give them a natural athletic appearance, although they still must pay attention to their diets since they tend to accumulate fat along with their weight gains.
At the core of the mesomorphs training program should be resistance training. Since mesomorphs muscles are so thick and powerful, moderate to heavy weights are required to stimulate growth. After a thorough warm-up, your target should be 3-4 sets of 6-8 reps with increasing weight load each set. It is important to strive for a solid pump. Start with 3-4 exercises per muscle group.
Remember, once your muscles have been properly stimulated, further stimulation doesn't equal larger muscles. Heavy weights is not the only way to go. Be creative, and try switching up the order of your exercises and the type of exercises. You may want to train with higher reps and lighter weight every now and then. Constantly challenge your muscle with a variety of stimulation. This helps minimize the risk of injury and help maximize your gains. Avoid overtraining, and pay attention to proper rest and nutrition for optimal growth and muscular development.
Although mesomorphs gain mass easy, they also gain some fat. How do you solve that problem? You guessed right...Cardio. Doing some form of cardio about 35 minutes 3 times a week should be enough.
When training regularly to build muscle, you'll need 1.5 or more grams of protein per pound of bodyweight. So a 200 lb bodybuilder should be eating 300g of protein or more per day. With increasing muscular demands your protein intake may increase as well. Try to get a protein: carb ratio of 3:4 (300g protein, 400g carbs). So if you are eating 6 meals a day you should get 50g of protein and 66g of carbs per meal.
Also, try to choose complex carbs with lower glycemic indices. You don't need to concern yourself with fats too much since they are limited by the type of protein you consume. If you eat red meat you should be getting enough, if you do need to add more fat do it in the form of nuts or flaxseed oil. You may want to increase your fats if your energy levels are low, and only increase carbs if your muscles appear extremely flat.