I can ejaculate from doing pull-ups.
I keep going and going till i start to feel it and then usually if i just hold the final one the contractions just kinda start and it just flows out.
It's a fun thing to try to do. it has to do with using the muscles inside your body and contracting them intensely. Usually helps too if i pull myself out of my jock or underwear i'm wearing so i can hang free.
I'm don't even get fully erect when it happens. Like i said; it's like an internal orgasm/contraction more than a penis stimulated reaction.
Fun to do. Feels great. It's intense and exhausting. Needless to say if I go for it I save it for the end of my workout!