I'm having the same problem. Now most of my solves average 5 seconds or so higher than before, and that's because my right hand has been strained. I just hope I don't lose the feel of the cube.
Sometime I have a so bad day that I want to crush the cube. But if you're finished with leaarning all the algorithms for friedrich, then it's just the look ahead again.
Don't take breaks?! LOL!!! That's like working at the gym EVERY SING DAY for 3 hours a day, and no breaks. LOL!!!
You are right about how stamina builds over time, but it builds by healing. Meaning if you want your stamina to build, you have to let it rest, and then it will get stronger. For example, if you work at the gym everyday, especially if you're young, your muscles are going to start to ache. Work at the gym every other day, so your muscle fibers GET A CHANCE to rebuild stronger, and then your muscle stamina will get stronger. If you don't let the muscle rebuild, and will just hurt more and more.
Same for cubing. If you have sore hands, you have to take a break. Then your hands will get stronger. If you don't take a break, how will your hands heal and get stronger?
OK, guys. This is getting to be a problem. Cooper, stop hunting down old threads. Pcwiz, read the f-ing dates. It's been 2 months now, I think I fixed my problem. I average 23+/-2 seconds. I don't think I need your help anymore.