Adding 580 EX ii flash

I am new to this forum, and am self taught, so you can imagine I need all the help I can get! I have mostly shot sports for several years now, and did about 10 senior shoots in the past several months... All of which I have done with natural light... I have purchased a 580 EXii canon flash for my 5D mark ii and don't know much about flash.... I am wondering if my understanding that adding the flash will freeze action faster? Because I read somewhere in tips to another that they did not have to worry about blur when holding their camera using a shutter of 40 because their flash would freeze the action.... Can any of you help explain this?

Thank you,
Lisa

Well before I started to learn about my flash I would shoot in program mode because I had not idea of what the flash was doing. In program mode which defaults the shutter to 1/60 I often had blurred hands from people moving them around while talking. Now I shoot in M between at 1/125 and or 1/200. I am just as interested as you are about this.

Flash freezing motion depends on the flash being the predominate light. If you have the camera set to expose the ambient light close to the light that the flash is producing then you will get blur. If you have the ambient exposure set a couple stops or more under the light the flash is producing then the motion will be stopped.

That makes sense. I sorta already knew that. Just curious in case there was something I did not think of.