Re: This is what happens to your chops after 120 days...
I'm familiar with the song, actually well enough to know what you're referencing. Having grown up on old-school thrash, I never alternate-pick chuggy stuff unless necessary for sheer speed. I get worn out fast now though. It's just a skill I don't use much now.
What's your right-hand (assuming you're right-handed) technique like? My friend I play bass for when we have a metal band going is all wrist action, total economy of motion. Actually, no, scratch that, for speedy stuff it's thumb and forefinger. Blows my mind to watch. We'd done metal before with both of us on guitars, and I am brute force forearm Zakk Wylde type to watch with the 3mm pick and the vintage-y pickups and giant strings, precious little gain and plenty o' hate.
I'm pretty friggin' sloppy with the alternate stuff on chord work too unless it's so damn fast it doesn't matter. Might just be all the years of downpicked chugging. I don't know.