Did they confuse 'invisible man' with 'invincible' man?

I honestly like this movie enough, I think that 5.8 imdb rating is really low. It's great up until the ending, where Kevin Bacon out of nowhere develops superhuman strength and invincibility! He's snapping necks, impaling people with crowbars like the people are made of styrofoam, holding grown men above his head by their necks, and then he survives getting torched with a flamethrower, beaten with a crowbar, falling several stories onto a moving elevator, getting severely electrocuted, and two explosions???

And up until that second explosion, he doesn't even seem phased by anything. He walks off getting set ablaze by a flamethrower as if a few bees stung him. And then when he falls for his death, I half expected him to climb back up the elevator shaft and keep fighting. It's ridiculous. Is there any explanation for this? One theory that attempts to justify it is that the invisibility serum basically fried his brain and nerves and made him immune to pain, but even then he still wouldn't get around long. If you got set on fire, pain wouldn't be your worst issue.