Off hand, the stupidest story I ever read and why I wondered even then why my mom bought me comic books or I guess slightly thicker sort of graphic novels (but I don't think this was exactly a graphic novel). The boxer wants to go up a weight class or something and figures if he takes the whole bottle of weight-gain pills at once he will gain weight faster which indeed he does; in fact, the surface of the earth no longer supports his mass (he becomes denser but not fat) and he falls through the surface deep underground.
The kicker is, he meets giant moles who want to use the man as a sparring partner and that becomes his fate -- boxing against giant moles (not mole people but giant, intelligent rodents) underground.
EDIT: Looking at the artwork at the link the answer provided, they apparently were humanoid creatures, not giant moles. I remembered that part wrongly.