To be clear, when I said that I didn't mean the joy is in chasing numbers. That's a bit reductionist. Some people enjoy that, but I was implying that the downstream effects of chasing numbers are the exciting part; challenging yourself and going through suffering to get a good physique or lift heavier things. Increasing reps/weight is the way to increase workout difficulty, thereby stimulating growth.

I don't think there's a fitness discipline out there that can put you in as much 'injury-free' pain as strength training does - at least, not acute pain like after a heavy leg press. It's almost sadomasochistic, which is why I think calling strength training boring is a little off the mark.