They say that Spider-Man may have the same kind of radiation that the Hulk has where he can grow in strength the madder he gets that might explain his fights with a clearly stronger BT Morlun Savage Hulk and Firelord. I believe there have been debate wether or not Spider-Man had then symbiote at the time when he fought Firelord but the last book in that sersi when he finally beat Firelord he had got muscle bound