They were members of the Canoeing club / Dragon Boat race team and were the Arnold Schwarzenegger type of men.
Another method is the Japanese Sumo wrestler method. From a documentary I saw, the sumo wrestler revealed that they ate a lot of food and went to bed immediately for naps. The SUMO way of gaining weight is to go to bed immediately after meals. It is not so effective to simply eat a lot of food and hope for weight gain to happen by itself.
i think the second method is suitable for my needs.