If you're using Project Blue (or Project Green I think) the script below should work:
desc = Sprint Script by Marc Steene
:state=0:etimerstart,state=1
:state=1,plrusingrun=1:state=2
:state=2,etimergreater=YOURSOUNDLENGTH:sound=$0,etimerstart
:plrusingrun=0:state=0
Set that in a trigger zone with your breathing sound in the Sound0 field. You also need to set the YOURSOUNDLENGTH to the sound length in milliseconds (e.g. 1000 = 1 second).
Please note - I haven't tested the script and wrote it without a guide in front of me so no guarantee it will work
[b]FPSC MIGRATION: http://forum.thegamecreators.com/?m=forum_view&t=142497&b=21