If I knew shit like 100 sets would make me any stronger I'd do it in a heartbeat.
I seriously doubt that increased strength is a factor of only neurological adaptation [100 sets takes synaptic facilitation to a whole new level]; you probably got bigger.
BTW, why MUST you feel pain??? There's no need to go to failure.
It's just the way I lift. Some people like going to failure, some don't. It's been debated alot and no one has really proven which way is better. I just like the burn, it makes me feel like I've accomplished something when it takes all the willpower I have to withstand the pain of one more rep.
Doing this may have made me stronger, but there is really no way for me to measure it now (I never did one rep maxes for curls). All I know is that pain/burn has been my limited factoring up until now, now it's how much I can do before I am too tired to lift anymore (funny thing is, this is what happen near the end of my 250 set day. I no longer had any pain/burn, and the only thing that stopped me from doing more reps is I was too tired to lift anymore).
I have no idea what is up with my arms. I can punch them and feel it, so I know I didn't fuck up my nerves or anything like that. It's just like when I lift, it doesnt matter how much I lift or for how long, it always feels like I just did my first rep everytime.
I did not get any swelling while lifting (you know how you muscles look bigger after lifting? I didnt get that). However I measured my arms today, it's been 3 days since i did my last lift, and they were .2 inch bigger. I guess they didn't hurt my growth, that's more than I grew from actually doing the 250 sets and all I did 3 days ago was 5x6.