Madonna, Kylie, Cher, Cindy, Pet shop boys, Celine, Donna was still touring just before she died ... & i'm sure there are dozens more (plus loads that aren't big in the US) and ofcourse all the rock acts like U2 that have been touring for 100's of years now
But i made my point wrong.... what i really ment to say was, the old school artists including janet didn't complain on their first tour(s) or got exhausted or overworked... They just did it