I know it sounds handicapped, but if you strain your legs and point your toes while you happen, it's more intense and pleasurable.
Also, if you do the aforementioned WHILE your jack off, it will make you happen very, very very quickly.
I also tense up my legs when I do it, you're right.
Nope.
I've heard it prevents cancer though.
It's like a car. If you don't turn on the car for three months parts will start to go bad.