Re: Dark Gate OOC Thread
Simple. Obviously the muscle guy in your example focuses mainly on exercises to make his muscles big and defined, whereas the thin person focuses on training entirely intended to boost their strength with their appearance as an afterthought, leaving the latter's functional strength actually greater than the bigger guy's. In addition, the thin person does a lot of cardio because they regularly practice ringen and have honed their grappling technique, while the muscular gentleman either has no such training in technique or is simply not as talented at it, so the latter gets outdone in positioning and gasses out leaving them at the thin person's mercy.
Oh, right, and in some cases there's also the whole magical corruption making warped and supernatural characters potentially powerthirst strong regardless of their builds. Can't forget that either.
Yeah though re. the original question, it's all GM discretion and how you roleplay your character. Personally, when I GM I tend to consider body to represent a character's potential level of physicality (including strength, endurance, durability, dexterity, even eyesight) and general martial skill unless the character's bio or the player's writing indicates otherwise.
To be a little more helpful: I think the examples given last were that 30 body was pretty average for physical labor jobs such as carpentry and farming, 40-50 body was considered pretty close to peak fitness, 60 body was considered Olympic athlete level, and 70 body was considered to be breaking into low level superhuman fitness.
Assuming the character isn't supernatural or warped, it's probably pretty safe around the 40-50 body mark to consider your character at least capable of lifting their own body weight given proper positioning and care, should you want to roleplay them as the lifting type, and by 60 they're probably looking more toward 2x. Most GMs will give extra consideration to more monstrous races or supernatural types as well.