Problem controlling player movement with keyboard

programming flash
1

I’m making a side scroller game and want to move the player across the screen using the arrow keys on the keyboard. I am able to move him fine, but he always seems to move over once, pause and then continue moving until i let go of the key. I want to get rid of that little pause that keeps occuring.

I tried to minimalize the code as much as I could and I was sure that having a loop to keep the player moving until the key was released would make it smooth, but the lag is still there.

Any ideas on why this happens or how I can move the player smoothly would be much appreciated, thanks!

var keyNowUp:Boolean = true;
stage.addEventListener(KeyboardEvent.KEY_DOWN, movePlayer);
stage.addEventListener(KeyboardEvent.KEY_UP, stopPlayer);

function movePlayer(event:KeyboardEvent)
{
    keyNowUp = false;
    do {
        player.x += 10;
    } while(keyNowUp = false)
}

function stopPlayer(event:KeyboardEvent)
{
    keyNowUp = true;    
}