"I think this is extremely pertinent in many sports. Inner doubt tends to express itself as muscular tension, which is results in breath holding. You are correct that you can't just tell some one to relax, but the verbal cue (bumper sticker) to "breathe" can bring instant and dramatic results. It's one of those detrimental things that you don't know that you are doing until some one reminds you. Free flowing movement comes from free flowing breathing."
^^^^^^The above can DEFINITELY be true for those that are less experienced at running gates. The tendency is to hold your breath--which is why in training it is something we mention to people. Perhaps just one word would suffice once an initial message or two was driven home.