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Besides keeping up with hydration and carbs, which electrolyte is most important in maintaining muscle endurance for longer rides like centuries? I'm guessing it would be potassium or calcium. Trying to plan ahead on which snacks or drinks to use for my next ride, RSVP, Seattle to Vancouver.

  • Could you please add some more information to your question. 168 miles? That's quite a ride. Is there support for the trip? Are you doing it in one hit or planning rest stops? What time of year and what temperatures is it likely to be? What's your cycling experience - how far do you ride each week ? – Criggie Aug 6 '16 at 1:29
  • It's the one you're about to run out of. (Hint: Calcium is never a problem so long as you still have bones.) – Daniel R Hicks Aug 6 '16 at 2:14
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    As altomnr suggests, you lose a lot of sodium in sweat, and it is certainly the electrolyte you need the most of in grams/hour or whatever. Potassium is #2. Most people don't lose enough magnesium to worry about, if they maintain normal nutrition. – Daniel R Hicks Aug 6 '16 at 12:03
  • Again, unless this is a race, just eat when you're hungry. – whatsisname Aug 6 '16 at 17:44
  • @DanielRHicks You're right that magnesium losses during exercise are insignificant, but magnesium deficiencies are very common and under-diagnosed because blood serum levels, which doctors use to diagnose it, are a very poor indicator. – Carey Gregory Aug 7 '16 at 23:18
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Most likely sodium.

However, a lot of it depends on the person. One person might need more of one electrolyte than another, so it's difficult to make a judgment on the order of your "most critical" electrolytes. A sweat test would be a great way of testing which it might be.

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    While Na is certainly a very important electrolyte, with a little care most will have sufficient intake to offset losses. One very important electrolyte that is often overlooked is Mg, which is critical in many metabolic pathways and is often deficient in our diet. It is often through to be a factor behind poor performance. – Rider_X Aug 7 '16 at 5:39
  • Agreed - magnesium is the one I have to focus on the most, personally, but sodium still has it beat in terms of quantity lost (typically). That's where a sweat test could be beneficial. – Altom Aug 7 '16 at 12:33
  • It has been estimated that 60% of all westerners are Mg deficient. This is because modern farming practices have depleted soils of Mg such that many foods that used to be high in Mg no longer are. To compound the problem, doctors typically rely on blood serum levels, which don't reflect deficiencies until they become severe. That's because the vast majority of Mg in the body is intracellular, so blood samples can't accurately measure it. And worse yet, it can take months of supplementation to restore normal intracellular levels. – Carey Gregory Aug 7 '16 at 17:40
  • Anyone with atrial fibrillation (which includes a LOT of endurance athletes such as cyclists) should probably take daily Mg supplements. Most cardiologists prescribe Mg supplements now for their afib patients for this reason. And for you guys and gals who have trained and ridden hard for many years, you should pay attention to afib news since it's quite possibly in your future. – Carey Gregory Aug 7 '16 at 17:43
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The five major electrolytes for endurance athletes are Sodium (Na+), Potassium (K+), Chloride (Cl-), Calcium (Ca++), and Magnesium (Mg++). Of these, I would say sodium is the most important one, followed by potassium.

Sodium is the most abundant and perhaps the most important of the electrolytes. Na+ is found in higher concentrations outside of cells in our bodies. All cells depend on sodium and potassium to bring nutrients inside the cell and to remove waste. Nerve conduction–a process important for thinking and for activation of muscles—is also heavily dependent on sodium and potassium. Sodium Chloride (NaCl) is table salt and often referred to simply as “salt.” Many foods contain sodium. Deficiency of sodium is called hyponatremia. Hyponatremia is the most common electrolyte disorder in the U.S. Hyponatremia in athletes is usually due to sodium lost in sweat. Other disease processes may cause hyponatremia, but the symptoms of hyponatremia are the same for athletes and non-athletes. These include fatigue, muscle weakness, muscle spasms or cramps, convulsions, nausea, vomiting, confusion, or decreased consciousness. Vomiting due hyponatremia can cause Na+ levels to drop even further. - A Tale of Five Electrolytes.

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    I wanted to give a shout out to Mg as "low Mg+ is often the reason for sub-optimal performance" - from your article. Mg is an important cofactor for many metabolic processes and most diets have Mg deficiencies, especially for endurance athletes who lose a lot of electrolytes through sweat. The other electrolytes are readily available through a variety of foods so deficiencies here are more easily prevented. – Rider_X Aug 7 '16 at 5:35

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