The reason behind this idea is simple; muscle is 3 times heavier than fat. Due to the nature that its density is high, it is easier for a person to become heavier even without much significant growth in the size of his body. However, this must be done with the right system in order to maximize the food that he or she ingests.
Next up, building muscle is also a good way to ensure that you still have the same metabolism rate. What this really means is that you have the option to lose weight or gain weight. In comparison to just eating unhealthily and being inactive, the muscular resistance training ensures that there is always a demand for the nutrients from the food you eat rather than let them collect and become unsightly fatty deposits all over your body.
One great thing about building muscle on top of a high calorie diet is the option for you to put on mass where you want. Normally, ectomorphs are unsatisfied with their narrow shoulders and thin limbs and that is where they can put on the weight by training those areas and gaining muscular mass there. When you experience growth in the places you would like to put on mass in, this strengthens the self-belief that you are in total control of their body. This will ensure that you feel more confident about yourself, fueling your desire to grow larger with more mass.
Next, muscle is lost slower compared to fats. Fat is always being used by an ectomorph as a fuel source constantly due to their high metabolism. Thus, the fat deposit in the body of an ectomorph is always declining. However, it is more difficult to reduce the weight of an ectomorph by decreasing the muscle mass in the person. This is because a muscle in a collective community of fibers and enzymes, with its own storehouse of energy source in the form of glycogen. The body can only lose muscular mass when the glycogen in the muscle has been removed and it is not replaced promptly. This ensures that even with a higher metabolism rate of an ectomorph, the body weight will decrease slower as compared to having a body mainly consisting of fat deposits.
Lastly, nothing is more satisfying for an ectomorph than the idea of finding their current clothing tight. When their small sized shirt is becoming tighter, it is an immediate gratification in 2 ways; knowing that they look good in what they wear now and the desire to shop for clothing that is of a larger size to continue growing. This sign motivates the ectomorphs to train even harder and to continue with what they have been doing right.