Moraghan, Dr (not that I am) TmR at your service..... the diaphragm is a muscle like any other, so my only suggestion is that you have strained it at some point in the past, and periodically you are aggravating it. But that isn't really consistent with only coming on in longer races, rather than when you are running faster, and breathing more deeply in shorter races. How long has it been around ? When did you first notice it ? What about in long hard training sessions ? I think you said the right side, so another possibility is that is is something to do with irritating a otherwise asymptomatic gallstone ?  Or do you get very stressed and breathing goes haywire in those 3k+ races ?
What: "track session" total 8ml, except that the track is still snow covered, but the trusty Uni RR was completely snow and ice free, so even did 2 laps are warm up, instead of usual road loop. Then 2 laps, 1 lap, 2 laps, 1 lap., 2 laps c M-tempo effort (each lap = 0.8ml)
Why: it's Tuesday, but a shorter than usual distance as a nod to tapering for the w/e
Edited: 12/01/2010 at 22:37