The luckiest body type of the three different body types. Called the "gifted" ones. This type is genetically prone to great muscular gains. Usually very athletic looking, with good posture and symmetry. For a bodybuilder or fitness model this is good news. Mesomorphs are said to build muscle faster than most people and are able to loose fat rapidly when on the right diet. Where the ectomorph and the endomorph both have a positive and negative side, the mesomorph has the best of both worlds.
Training:
The best type of training is said to be achieved with heavy weight performed explosively (with great force output, intensity). Super sets, Compound sets and giant sets are useful here as they can produce significant gains. Always allow proper recovery, rest and variety as this style of workout can easily lead to overtraining!
Cardiovascular exercises should be done 2-3 times a week for about 20-30 min per session. Intensity wise, moderate to high for fat burning purposes. Don't go over board as it is believed that Mesomorphs could loose lean mass if cardio is too long or frequent!
Diet:
Protein is the key. So be sure to get quality protein daily along with moderate amount of carbohydrates (preferably low glycemic ones) and fat. Ideally, a Mesomorph should avoid weight fluctuation in order to gain or retain mass. Adopting a diet that is rich in nutritious and "clean" food will help you to keep your appetite and energy level stable (satisfied) and avoid cravings.