Every time I pool swim, I seem to urinate a lot afterwards. Swim, shower, urinate, get dressed, walk back to my office, and then have to urinate again 10 minutes later.
What’s up? It doesn’t happen during a race, but then I don’t eat or drink three hours before sprints or olympic distances races.
Is this a survival mechanism? Does my body say, “hey, maybe we should conserve body heat by getting rid of some of this excess fluid”?
Or, is this some kind of blood volume reduction thing?
The external hydrostatic pressure due to being immersed in water* causes a shift in blood from the periphery to the central circulation, which the body senses (via stretch receptors) as meaning that blood volume is too great. This in turn results in changes in hormone secretion (i.e., reduced secretion of ADH) that result in less reabsorption of water in the kidneys, and hence an increase in the rate of urine formation.
*Being horizontal for a prolonged period of time may also be a contributing factor, but clearly isn’t necessary to cause diuresis.
Of course, that’s what I meant, either way if it’s a physiological response it should happen everywhere, but maybe the stress of races overrides it
IME as a diver, it’s cumulative. By the 3d or 4th day of a dive trip I am peeing like a racehorse during the diving (also contributed to by drinking more water, but not THAT much more… sheesh)
I always assumed it was because in a race you exit the water and immediatly begin to sweat (on the bike) thus lowering excess fluid but maybe AC360 has the scientific answer…
Of course, that’s what I meant, either way if it’s a physiological response it should happen everywhere, but maybe the stress of races overrides it
Presumably one is exercising at higher (sustained) intensity when racing, which would divert blood flow away from the kidneys and hence diminish urine formation.
(BTW, free water clearance by the kidneys actually increases slightly during very low intensity exercise, due to the rise in mean arterial blood pressure…something to keep in mind the next time you go on a recovery ride with a slower cyclist!).
Of course, that’s what I meant, either way if it’s a physiological response it should happen everywhere, but maybe the stress of races overrides it
Presumably one is exercising at higher (sustained) intensity when racing, which would divert blood flow away from the kidneys and hence diminish urine formation.
(BTW, free water clearance by the kidneys actually increases slightly during very low intensity exercise, due to the rise in mean arterial blood pressure…something to keep in mind the next time you go on a recovery ride with a slower cyclist!).
Oh, come on, now you’re just making shit up…
In addition to the hydrostatic pressure effect, my understanding of muscle physiology is that each molecule of glycogen is stored along with 2 molecules of water (or it could be more than 2, I can’t recall exactly). When glycogen is burned, the chemical bonds between the water molecules and the glycogen molecule are broken and the water is “liberated” into the muscle cell. The excess water will come out as sweat if you are sweating but, if swimming in cold water and not sweating or hardly sweating, almost all of that water comes out as urine. Thus if you swim in an 88 degree pool you’ll generate a lot less urine than in say a 74 degree pool, assuming no wetsuit. Similarly, if you go out for a bike or run in cold temperatures and aren’t dressed warmly enough to sweat much, you’ll also have to urinate more frequently than if you wear more and sweat more. The urination on a cold bike ride is probably less than during a cold swim to to the hydrostaic pressure effect that Dr. Coggan discussed.
Also, Dr. Coggan, I have a question: Most of the time when I swim I am not completely immersed in water but rather my shoulders, arms, and part of my head is out of the water quite a bit. I would think this would affect the hydrostatic effect somewhat??? This is the first I’ve heard of this effect but then I’ve mostly read exercise phys.
TC - I sweat very, very little when the water is cold. I’ve swum 6000 yds and weighed myself before and after and only lost like 1 lb, almost ALL of which came out as urine in 2 trips to the bathroom during the workout. I didn’t collect the urine and weigh it but it was quite a bit both times.
The thing that clenches this debate for me is the huge difference in the amount I have to urinate when swimming in a hot pool versus a cold pool. I sweat a huge amount in the hot pool and urinate very little versus LOTS of urine when in a cold pool for same workout.
