dear Hoegaarden man and tonywoodall,

I particularly like tonywoodall's approach to solving musculoskeletal problems and much of the doctrine i adhere to when there is a need for it. However, I personally find it difficult to conclude on what a problem is with very little information. This is clearly some fault in my ability to clinically reason a problem. Having said that, there are so many reasons why you would have groin pain especially when you sprint and in no other activity (i am assumming this is the case)...also there is a reason why this flares up lasts for two days and then goes...
I will not jump to the conclusion that it is a sacroiliac problem however i would acknowledge that it could be. again more information is needed..

i.e, after the sprint due to find it hard to weight bear? do you get it at the start of the sprint or at the end? is there any other movement that brings this problem up? e.g stair climbing, hip movements, lower back movements... after your sprint and you have a flare up, is there a position that eases it? does it disturb your sleep?

stress fractures can occur in sprinters to be honest...so is osteitis pubis, so are adductor strains...to conclude that the problem is from the spine automatically with authority shows an expertise that very specific to experience..
if you can give us more information, then maybe we could help reason out the problem...in the end nothing beats having a hands on assessment
cheers