Things runners never say #1 hematuria

It turns out a lot of runners experience it at some point. Blood in your urine. It can certainly give you a fright and send you running to your GP. While it actually should (because there may be several reasons for passing blood through the urinary tract which are not exercise-related), there is no need to panic if you're not experiencing pain and the red hue does not persist a few hours after you have stopped exercising.

Apparently, there are as many as three (!) reasons for passing blood through your urinary tract (a.k.a. Hematuria) that are induced by running itself. Gross? Good news is, it could be worse :) Welcome to the world of endurance running!

1. Footstrike hemolysis / mechanical muscular trauma
   The reason for blood in your urine may actually lie in your...feet. The foot strikes, repeated several times over a few hours, especially on hard surfaces, cause damage to red blood cells in the feet and releases haemoglobin into the bloodstream, whose excess is then lost to the urine. This type of hematuria is actually called haemoglobinuria.
2. Microscopic lesions in the interior wall of the urinary bladder as a result of bladder-jostling on the run
   We all know that if you are a runner, you are prone to injury sooner or later...but we often associated 'running injuries' only with the musculo-skeletal system. But would you think you can actually injure an internal organ while running? Well, now you do! The impact of your foot strikes, especially if you are running on hard surfaces without sufficient padding, can cause trauma to the delicate walls of the urinary bladder, causing tiny capillaries inside to bleed and tint your urine. If hematuria has happened to you after a long run before, do not urinate later than 30 minutes before exercise. The little urine in your bladder may prevent the bladder walls from making contact and alleviate the symptoms.
3. Increased permeability of the glomeruli
   Strenuous exercise has a serious impact on the renal function. It is estimated that the renal blood flow may drop to 25% of its resting value. This changes the permeability of the glomeruli. The increased glomerular permeability allows the red blood cells to pass to the urine, thus colouring it before normal filtering capacity is restored.

All in all, passing blood into your urine after strenuous exercise (especially a marathon or half-marathon) has several physiological causes and is not as serious as it may seem. However, if it has happened to you for the first time, you are experiencing pain or the blood remains in your urine several hours after you have stopped exercising, it is important to consult your physician, as it may also be a symptom of an infection, kidney stones or a tumor.

Read more: http://www.ncbi.nlm.nih.gov/pubmed/6567229

http://www.time-to-run.com/doctor/bloodyurine.htm

http://link.springer.com/article/10.1007/s004210050480#page-1