how are blood vessels under the feet not compressed to the point of blockage when standing?
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Actually they are. But you naturally shift every few seconds. If you don’t, lactic builds up and it starts to hurt, very subtly at first, so you shift without noticing.
This is why paralyzed people get bedsores. They can’t shift. It happens even lying down.
Most of the blood vessels in your feet is deeper in your foot. The underside of your foot is a thicker layer of skin and then layers of harder fat so that the weight gets distributed into your bones without compressing the blood vessels. You still do not get around the issue though as there is some smaller blood vessels that need to supply the skin and fat with blood. Again the thicker skin helps as the blood only needs to get to the inner part of the skin. And in general skin and fat does not need much blood anyway, not like muscles or inner organs. Your cells do not need a constant flow of blood but can handle shorter disruptions in blood flow. Although not recommended your extremities can be without blood flow for up to 15 minutes without needing treatment. But skin and fat can usually last much longer then this. It is however almost impossible to stop blood flow completely. And you do not tend to stay completely still for longer periods of time either and will move around a bit. The problem you are describing is however an issue in certain environments, for example on airplanes where the seats are tight and does not allow for much movement.
To add, because I didn’t see it mentioned, you find an increased number of red blood cell fragments in blood samples taken after running long distances.
The impact and squishing of the vessels in the feet is enough to crush some of the red blood cells in those vessels.
Standing does restrict blood flow in the feet, but you don’t stand perfectly still very often. You shift your stance, fidget, rock back and forth, pace, the works.
This can be a problem soldiers face when on parades or in boot camp, where they sometimes have to stand perfectly still for long periods. In the Air Training Corps, I was taught how to shift my feet a tiny bit to relieve pressure while not being too noticeable when standing at attention – and if you pay really close attention to videos of soldiers standing at attention, you’ll notice them fidget their feet a tiny bit now and then.
Have you ever seen a video of a soldier on parade stood still for so long that they faint? That.
When I was in the forces, you’d see it a good few times a year with the odd bloke breaking their nose.
I used to do security. Had a lot of standing in one spot in that job. At one point I had stood in the same spot, not moving enough that I had caused a small blockage stopping enough bloodflow that I ended up nearly passing out.
Crazy feeling when that happened. I was fine, then suddenly I felt a cold shiver creep up my legs and when it hit my head I nearly fell over immediately. Coworker noticed me go pale, sat me down gave me some juice and a few minutes later I was fine.
Wow so many wrong answers. Whew.
The correct answer is that there’s this thing called the hydrostatic effect – the taller a column of fluid, the greater the pressure at the bottom. So the normal systolic blood pressure in your feet is usually 200 or higher, compared to the “normal” reading of 120 at the level of your heart. This pressure is enough to overcome the compressive forces on the soles of your feet and perfuse the tissue.
The *many* wrong responses that you “shift your weight” don’t know what they’re talking about. That’s something you don’t utilize the skeletal muscle pump to increase venous return since veins are highly compliant. People pass out when they lock their knees because that requires sustained muscle contractions (instead of rhythmic contractions), and de-activates the skeletal muscle pump.
And the “lactic acid causes pain and hives you he’d sores” is maybe the strongest thing I’ve read today. That’s impressive.
I had to read this while walking in my socks on the treadmill, didn’t I…
Sorry feet blood cells. 🙁
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