‘At the ripe age of 55, I made it to the finals of my tennis club’s singles tournament, facing a spry opponent two-thirds my age. Absurdly, he was named Cort.
I won the first set; the second went to a tiebreaker, and he nosed ahead 6-5. I kicked a serve down the T, then patiently waited to pounce. Finally, Cort hit me a short ball low to my backhand. I like it there and sprang into attack mode, hitting an inside-out slice that landed in the far corner and swerved off court. But Cort is a bloody jackrabbit, 125 pounds wet, and retrieves everything. He’s there in plenty of time and whips a redirected backhand down the line for a winner. Dejected, I looked up at the sky toward some imaginary tennis God in a golden fleece Fila jumpsuit and pondered the injustice of it all. Now I had to play a third set. I was running on fumes, and after a grueling rally, my left calf decided to turn into a fist.
I crumpled to the hard, hot court, writhing. Incongruously, Tennis Jeff checked out, and Science Jeff appeared with his clipboard. What was going on inside my malfunctioning muscle? Hmm… a supply-chain issue involving three elements from the periodic table and the electrical wiring of my own nervous system. Needless to say, I didn’t bring home the trophy. But I did learn something. What happened to me on that court turns out to be one of the more elegant stories in human physiology: a yin-yang balancing act between sodium, potassium and magnesium that never stops, whether you’re two games from the club championship or just sitting here reading this essay.
Every neuron in your body sits at rest in a state of electrical tension, with sodium camped outside the cell and potassium inside. The sodium-potassium pump, powered by ATP, spends energy around the clock to keep that tension in place, pumping three sodium ions out for every two potassium ions it lets back in. It is a tiny cellular tollbooth that never closes. When a signal needs to fire – a thought forming, a foot deciding to plant, a serve toss timed to the millisecond – sodium channels snap open, sodium floods in, and the cell’s polarity flips for an instant. This is depolarization, and it sends a wave traveling down the length of the nerve’s axon. Then potassium rushes back out, restoring the negative charge (repolarization), and the whole system resets for the next signal. Sodium in, potassium out. Push, then pull. Squeeze, then release. It’s the same teeter-totter logic that runs the rest of the body – stress and recovery, exertion and rest – just wired down at the cellular level. Magnesium is the outsider in the throuple, less celebrated than sodium and potassium, but just as load-bearing. It has two jobs. First, it powers the sodium-potassium pump itself; without magnesium, that tollbooth stops collecting. Second, it acts as a gatekeeper, holding the cell’s calcium channels shut until they’re needed.
And calcium is the ion that actually gets things done. In a nerve terminal (the end of a nerve cell where it connects to a muscle fiber or the next nerve cell across a tiny gap called a synapse), calcium flooding in triggers the release of a neurotransmitter, passing the signal along. In a muscle cell, calcium flooding in binds to a protein called troponin, which shifts a second protein out of the way and finally lets the muscle’s fibers grab onto each other and pull. That handshake between fibers is a muscle contracting – exactly what my calf was trying, and failing, to do at 4-4 in the third set. What most conversations about hydration miss is that water alone can’t run any of this. Water is the medium. Sodium, potassium, and magnesium are the current. Drink a gallon of plain water without replacing the minerals, and you can dilute your way into feeling worse, not better.
I find something cosmological in the fact that sodium, potassium, and magnesium are not exotic. They are stardust forged in the crucible of supernovas, ancient elements created long before nervous systems existed to use them. Biology assembled them across a membrane to push and pull against each other in perpetual disequilibrium… to produce a thought, a heartbeat, a topspin forehand. Which brings me back to my left calf. I can’t prove that a better electrolyte strategy would have saved me that day. Exercise-associated cramps are complicated creatures. But after several hours of sweating on a hot court, I was asking my nervous system and muscles to keep firing while steadily losing some of the very minerals that make that electrical machinery work.
That’s the case for electrolytes. Hydration isn’t simply about replacing water: sodium, potassium, and magnesium play essential roles too. When you sweat, particularly for hours, replenishing those minerals along with water gives your body the raw materials it needs to keep doing what you want it to do.* So next year, I’m showing up properly hydrated and loaded with electrolytes. Because if I’m going to lose to speedy old Cort, I’d prefer not to blame the periodic table.’
Jeff, Onecommune
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