Health Trivia : physical constitution easy to gain weight

Is there any physical constitution easy to gain weight?
 

The physical constitution hard to gain weight is that a body is flexible. 
Conversely it is easy to gain weight if a body is inflexible.

The reason of gaining weight is that fat is not burnt. It is mitochondria that burns fat.

If a body is inflexible, muscle does not stretch. Blood vessel in such muscle cannot send fat to mitochondria. 
Thus, fat is accumulated to the body without being burnt.