The layman thinks it is hard to run an ultra because of the great distances involved - I get tired just driving that far. Yet foot problems and stomach woes are more threatening to the ultra runner than covering a lot of miles. Effective digestion requires a sufficient supply of sodium ions. The biochemistry of that is beyond the scope of this forum, so let‘s focus on the connection between foot problems and sodium. Consider the typical ultra runner standing at the starting line. The feet are fine, the stomach is fine and the amount of sodium ion in the runner‘s blood plasma is fine. If those stayed the same during the run, the only factor in finishing would be the runner‘s ability to overcome muscle fatigue in the last part of the run. As the runner proceeds down the course, the body sweats for cooling effect( running generates a lot of un-needed heat that has to be removed from the body ). Sweat normally contains the electrolyte ions found in blood plasma. The primary ion in sweat is sodium. Potassium amounts in sweat are considerably lower. Other ions such as calcium, magnesium and iron are present but in very small amounts. As sodium is lost in sweat, more and more of it is pulled from the blood plasma. There is a normal level of sodium in plasma, and body must maintain the plasma sodium concentration within a tolerable range. If the sodium concentration falls too far outside the range, it can cause death. As you might suspect, the body has regulation mechanisms to avoid such a catastrophe. If you have too much sodium, thirst increases to prompt drinking water that can dilute or flush away any extra sodium. If you have too little sodium, the body must get more sodium or remove water from the blood plasma. This will lead to an increased desire for salty foods. If sodium is not ingested, then an alternative mechanism must be used. Your body can move water from your blood plasma and put it into extra-cellular spaces between tissue cells. That lowers the amount of water in the blood plasma and returns the ratio of sodium to water to an acceptable level. That ‘s good for your blood stream, but what about that water sitting out there between the cells? The cells that were compact now have water around them and that means the mechanical strength of the cellular structure is compromised. What is unfortunate for ultra runners is that the water will collect in the hands and feet because of gravity. It may be alarming to see your hands swell up, but it usually won‘t knock you out of an ultra. The big problem is found in the tissues of the feet. As you know from this forum, your feet are complex structures that bear strong and repetitive insult from the hours of running. Life is hard enough for them even when they are not compromised with extra fluid. When the fluid in extra-cellular spaces gets to be significant, mechanical strength is reduced. The feet swell inside the running shoes, putting extra pressure on the tissues, and those tissues can be rubbed to the point of physical damage. We see blisters form as layers of skin separate, and we see toenails move more, damaging the weakened tissues that normally anchor them. If one is not aware of the part electrolyte status plays in tissue strength, it is tempting to blame the socks and/or running shoes. Now, if these give you problems on short runs, the blame is well founded. If you run four consecutive runs that total 40 miles, and the shoe/sock combination works fine, but a single run of 40 miles produces problems, maybe something else is going on. Another tip-off is related to temperature while running. If your feet do just fine in cold weather, but have problems in hot weather, it could well be a symptom of poor electrolyte status. Runners sweat less in the cold, and sodium is not quickly lost. When the temperatures climb, sweat rate increases and the loss of too much sodium causes problems at a shorter distance than in the cold. Runners in cold northern climates rarely have blister problems during cold long runs, but can have blisters arrive during longs runs when the first hot days of Spring arrive. In my personal experience, electrolyte status made a big difference in the frequency of black toenails. Before I made my own electrolyte supplement, I had six to eight black toenails on a regular basis, just like many of my ultra-running friends. When I got the hang of how to use the supplements, my black toenails gradually healed and I ran ultras for five years with no more toenail problems. I made no significant change in shoe or sock type. In terms of terrain, I actually ran more difficult terrain over those five years. Sodium intake can be on a hit-or-miss basis, taking whatever might be salty from the aid tables, or it can be controlled by taking a supplement. I developed SUCCEED! Buffered Electrolyte Caps ( S! Caps ), with 341 mg of sodium per capsule so I would know exactly how much sodium I was getting throughout a run. While individual results vary, low-sodium problems can be avoided by taking one capsule per hour, with water. Since I‘ve used them, blisters and black toenails problems are a thing of the past. Copyright 1999 Karl King, all rights reserved.