why do i taste rust or metal in my mouth after running for a long period of time?

It's probably blood. You should drink more water when you run and throughout the day, because all that running dries your mouth and nasal passage out (because of the constant heavy breathing), and could be making your throat raw. That's prob. why you taste blood. Rule of thumb is to drink half your weight of water in ounces (Ex.-you weigh 150 lbs., then drink 75 oz. of water per day), and drink a little extra on the days you work out or sweat a lot.

Here is a true , medical based answer...

http://www.runnersgoal.com/why-do-i-have-a-metalli...

I did a little research and you know what it is? It is actually a mild form of heart failure. That sounds super scary but it is actually not that uncommon and is really just a sign that you are exerting yourself beyond what you heart was able to keep up with.

How the Heart Works

So how does the human heart work anyway? We all know that the human heat is nothing more than a pump to keep the blood circulating through the body to keep us going. It is actually pretty interesting how it works.

Blood flows through the heart in one direction, from the atria to the ventricles, and out of the great arteries, or the aorta for example. Blood is prevented from flowing backwards by the tricuspid, bicuspid, aortic, and pulmonary valves.

The heart acts as a double pump. The function of the right side of the heart is to collect de-oxygenated blood, in the right atrium, from the body (via superior and inferior vena cavae) and pump it, via the right ventricle, into the lungs (pulmonary circulation) so that carbon dioxide can be dropped off and oxygen picked up (gas exchange). This happens through the process of diffusion.

The left side collects oxygenated blood from the lungs into the left atrium. From the left atrium the blood moves to the left ventricle which pumps it out to the body (via the aorta) to bring oxygen to the body.

Heart Underperformance

Typically when you are resting or exercising you are at an equilibrium in that your heart is normally pumping out exactly as much as it is pumping in. This system usually runs very smoothly, resulting in the proper flow of blood. Nonetheless, if one element of the pump is not performing at full capacity, fluid can accumulate in unwanted places. If your left ventricle is not able to pump blood out of the heart to the body at the rate the right ventricle pumps it into the lungs, fluid accumulation in the lungs can result. This is sometimes referred to as a pulmonary edema.

So Why Do I Taste Metal?

Our red blood cells contain hemoglobin, a highly efficient molecule whose purpose is to collect and transport oxygen. Hemoglobin is carried around in groups connected by a central iron ion (Fe).

When you are overexerting yourself, fluid can accumulate in the lungs where some of the excess red blood cells can accumulate in and be transported to the mouth via phlegm (nasty I know…). Our tongues carry receptors that respond to iron (Fe) by sending a signal to our brains that we sense as a “metallic taste.” Whether you taste blood or “metal” it is basically the same mechanism at play.

This Sounds Bad – Is it?

In short, you have a metallic taste in your mouth during strenuous exercise because your heart is unable to keep up with the physical demands you are placing on it. Is this a sign of really bad things? Not necessarily. Particularly is there are no other symptoms of concern.

Our bodies are capable of dealing with this mild form of cardiac underperformance. You will typically experience relief from the symptoms when you stop exercising and resting for a bit. By resting a bit you are decreasing the demand on the system and the left ventricle is able to catch up to the demands of the right ventricle. The fluid is thereby cleared out and red blood cells are no longer accumulating in the lungs.

According to the experts, actual heart failure produces additional symptoms including shortness of breath. This is accounted for by an even more extreme accumulation of fluid in the lungs than is expected during strenuous exercise. One could also expect persistent coughing or wheezing, buildup of excess fluids in body tissues (i.e., swelling of feet, ankles, legs, etc.), fatigue, nausea, confusion, impaired thinking and increased heart rate.

If you do not have these sort of symptoms, you probably just over did it a bit on your run so the next time you try to chase someone up the side of a mountain, well just let them go…

you are dehydrating yourself, drink more water.

are you saying a mile is a long run?