People keep wondering why at 32, with a child, and with no time to do sports at all, I have abs that have put Marines' to shame (this is fact). And I really can't tell them; but I will tell you.
I've never been able to have an orgasm by touching myself. It just won't work. It's a bit like tickling myself: it doesn't have the same effect as when someone else does it.
When I was a student, visiting the gym, I got introduced to this great machine for ab training, something to do hanging leg and knee raises while you hang supporting yourself on your lower arms, and with a panel that supports your back. I found that raising my knees, and then bringing my legs down, gave me the most intense feeling, and started to use the machine often to reward myself for a tough workout, coming without anyone noticing (easy to disguise if you're huffing and puffing from the cycling already); it got so bad that I had to start wearing thin inlays and when there weren't many people around managed to work in 3 orgasms-and much more of the other work-outs, so it wouldn't stand out.
At home, I don't have the machine of course, but I found that when I lie down on my back, find a hold for my hands, and put a pillow under my waist, making the same moves imagining the wildest scenarios will always get me off, between 1-5 minutes.
If you're just starting out with this, it might take some time and you'll have a muscle ache, but for me, it is totally worth it. Getting at least one or two orgasms in, even on a busy day, and as a bonus a never-expanding belly.