As has been said it's mostly confidence. Being confident makes you relaxed. If you're relaxed, your muscles aren't all tensed up, if you're not all tensed up, you last longer. But there's something to be said about being bigger, and having to slower to start. It kinda forces me to calm down and take it easy so that I don't hurt her. Her warm up time, getting used to me, is a good warm up time for me, too. It's like exercise and sports. If you properly stretch and warm up before a game or workout, then you tend to be able to play/workout more before you get gassed. The same seems to apply to sex in my experience.
Also! Bulls, generally, tend to be in really good physical shape. It's part of the confidence, but also stronger legs and pelvic floor muscles mean more stamina, too. I strained a pelvic floor muscle in an accident about 6 years ago, and it took years for me to get my stamina back from that. The muscles just didn't listen to me anymore. Lots of squats, kegels, and stretches over about a 2 year period before I had my stamina back, and it's still, even now, not completely 100%. Every once in a while the it just will not be controlled.
Also! Bulls, generally, tend to be in really good physical shape. It's part of the confidence, but also stronger legs and pelvic floor muscles mean more stamina, too. I strained a pelvic floor muscle in an accident about 6 years ago, and it took years for me to get my stamina back from that. The muscles just didn't listen to me anymore. Lots of squats, kegels, and stretches over about a 2 year period before I had my stamina back, and it's still, even now, not completely 100%. Every once in a while the it just will not be controlled.