Vamp:
This is a science. Sheldon somatotyped over 100,000 people in his life time.
Here are some of the myths about body type.
1. It is a myth that anyone can get fat if they eat enough. Ectomorphs would physically die if they cramed their short intestinal length with enough food to make them obese. Endomorphs can have intestines up to 45 feet long. Ectomorphs as short as 15 feet.
2. It is a myth that if an endomorph goes on a starvation diet that they will become an ectomorph. A starved endomorph doesn't even look like an ectomorph. A starved endomorph looks like an emaciated ENDOMORPH. If you took two people the same height and same weight and stood them before me in swimwear I could easily pick out which one was the endomorph. This is why Endomorphs need to radically alter the type of food they consume for permanent weight loss. They need to fill that 45 foot long food processing tube with lots of raw vegetables. On the other hand Ectomorphs need concentrated foods in small amounts throughout the day because they don't have reserves of fat for energy. Ectomorphs move their food fairly quickly through their 15 feet of intestines.
3. It is a myth that anyone can become a mesomorph by following a vigorous program of weight lifting. The Trunk Index is changed very little by weight training. Most of the muscle mass that is added is in the arms and shoulders which isn't calculated into the Trunk Index.
To understand Sheldon's method you really need to understand the Trunk Index. This is how the Trunk Index is determined.
1. You have a photograph of a person. Preferably enough of the body is exposed to determine the critical measurement points. You need a planimeter which is an instrument for measuring irregular areas. You determine two areas on the photograph. One is called the Thoracic Trunk and the other is the Abdominal Trunk. Basically we are dealing strictly with the Torso (body excluding head, arms and legs). The dividing point between the Thoracic Trunk and the Abdominal Trunk is a line midway between the anatomical waist and the top of the pelvis. The Trunk Index is determined by dividing the area (obtained using the planimeter) of The Thoracic Trunk and dividing it by the area of the Abdominal Trunk. As the abdominal trunk area gets larger the Trunk Index becomes a smaller number. So here are some Trunk Indexes that will give you an idea of how they vary. (Trunk Index abbr. TI)
Extreme Endomorph Endo 7, Meso 1, Ecto 1 Height 62.4" Weight 219@50 TI = .85
Extreme Mesomorph Endo 1, Meso 7, Ecto 1 Height 62.4" Weight 144@50 TI = 2.05
Extreme Ectomorph Endo 1, Meso 1, Ecto 7 Height 69.6 Weight 106@50 TI = 1.45
Balanced Endo 4, Meso 4, Ecto 4 Height 70.8 Weight 186@50 TI = 1.45
I can figure this out for about 1,800 combinations using a 13 point scale (using .5 increments for 7)
It is possible for a person who has worked with this system to be fairly accurate with guessing, but it is really best to have a proper photograph.
If you aren't familiar with the system don't even think that you can guess. But, please don't dismiss it just because you don't understand it.
Also, the written test some of you have been referring to is practically worthless for figuring out your somatotype.
A lot more on my website.