I'm OK to stand some while riding outside, though I don't love it. I find it harder since I've switched to bar end shifters (though I otherwise love them, and won't go back).

On the trainer inside, though I cannot do the standing sets on Spinervals (I posted here a while ago seeking advice). Just can't do it. Especially the low resistance ones.

Elliptical is my cross training form of cardio, so I don't think it's that I don't have the right muscles....