I am going to take a slightly different track and forgive me if this sounds preachy. I am a physical therapist that treats pelvic floor dysfunction along with the general patient population.
Just because it may be common to do something does NOT make it normal. It is not normal to pee yourself - even with a hard effort. The even sadder thing is that we (as women) tend to chalk this up to a hard effort, changes with children, etc. You do not have to pee yourself to work hard in a workout.
This is actually pretty common in young, athletic women. It does not necessarily have to do with 'weak' muscles. Often in my super fit athletic women (especially cyclists) I see excessively tight pelvic floor muscles, which can no longer function properly in their job and can lead to incontinence.
So what to do - if it happens once, maybe not a huge deal for you. But if it happens every time you run, all hard efforts, etc and you ignore it, you are potentially solidifying poor motor control of your pelvic floor. You can seek out a pelvic floor specialist in your area. Request a referral from your OB-GYN or GP. I have found some MD's are more than happy to refer and some prefer to try other alternatives first.
Finally, just a thought - there are all sorts of reasons you could have been 'wetter' - maybe it wasn't urine, but other bodily secretions.
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