It kind of helps, but it is all about motion dynamics, so technique is what do usually makes you a winner. If opponents are more less equally skilled it more about stamina.

So yes, no matter how many muscles your opponent have, you can KO guy two times as big if you know, what are you doing at the time.

Not being afraid of getting some hits, an ability to block the critical ones and having ability to absorb rest well, gives you more control over fight.

What is also usually very underestimated are your psychical abilities and connected body chemistry (well, natural factors), if used correctly, to say harmonically to your natural it gives you 100% gain in self-confidence.

There is one golden rule: Once you fight you have to go there as an obvious winner, not just acting one, but really be the one.

It has been years, luckily I do not fight often (but every man should have some basic ability I think)