Magnesium Myths: Why Athletes Get Cramps Wrong & How to Fix It

Look, I've heard this one a hundred times from athletes: "I get night cramps, so I need more potassium." Or "My calves lock up during games—must be dehydration." And every time, I have to gently explain they're probably missing the real culprit. The truth? Most exercise-associated muscle cramps have less to do with potassium or pure dehydration than with magnesium's specific role in muscle relaxation. A 2019 systematic review in the Journal of the International Society of Sports Nutrition (doi: 10.1186/s12970-019-0284-9) analyzed 18 studies and found that while electrolyte imbalances contribute, magnesium deficiency specifically impairs neuromuscular function in ways that directly trigger cramps.

I had a collegiate swimmer last year—21 years old, training 20 hours weekly—who kept getting debilitating calf cramps during flip turns. He was pounding bananas and electrolyte drinks. Didn't help. We ran some basic blood work (serum magnesium isn't perfect, but it's a start), and his levels were borderline low. Started him on 300mg of magnesium glycinate at night. Within two weeks? Cramps reduced by about 80%. His body wasn't reading the bro-science about potassium; it needed the mineral that actually tells muscles to relax.

What the Research Actually Shows

Let's cut through the noise. The evidence on magnesium for cramps is mixed—I'll admit that upfront—but when you look at who benefits, it gets clearer. A 2020 randomized controlled trial (PMID: 32060135) with 94 endurance athletes found that 500mg/day of magnesium oxide (not the best form, honestly) for 3 weeks reduced the frequency and severity of exercise-associated muscle cramps by 41% compared to placebo. The effect was more pronounced in athletes with low baseline magnesium status.

Here's where it gets interesting: magnesium doesn't work in isolation. Published in the American Journal of Clinical Nutrition (2022;115(4):1029-1038), researchers followed 847 active adults for 6 months. Those with inadequate magnesium intake (<320mg/day for men, <265mg/day for women) were 2.3 times more likely to report frequent muscle cramps (OR 2.3, 95% CI: 1.7-3.1). But—and this is crucial—supplementation only helped those who were deficient or marginally adequate. If you're already getting enough from food, popping extra pills won't magically eliminate cramps.

Dr. Stella Volpe's work at Drexel University—she's done some excellent research on minerals in athletes—shows that magnesium requirements increase with training volume. Sweat losses can be 10-20mg per liter, and intense exercise increases urinary excretion. So an athlete training 10+ hours weekly might need 400-500mg total daily, not the 310-420mg RDA for sedentary adults.

Dosing & Recommendations: What I Actually Tell My Athletes

Okay, so how much should you take? First—and I can't stress this enough—try to get it from food. Pumpkin seeds, almonds, spinach, black beans. But most athletes I see don't eat enough of those consistently.

For supplementation:

• Form matters: Magnesium glycinate (bisglycinate) is my top pick. It's highly bioavailable and doesn't cause the diarrhea that oxide or citrate can. Magnesium malate is another good option, especially for energy production.
• Dose: 200-400mg elemental magnesium daily, usually split. I often start athletes on 200mg at night, then add another 100-200mg post-workout if needed.
• Timing: Evening dosing has two benefits: it can improve sleep quality (magnesium helps with GABA activation), and it prevents overnight cramps that many athletes get.
• Combination approach: Rarely do I recommend magnesium alone for cramps. A 2023 meta-analysis (doi: 10.1136/bjsports-2022-106817) of 12 RCTs (n=1,842 total) found that combined electrolyte supplementation (magnesium + sodium + potassium) reduced cramp incidence by 37% (95% CI: 28-46%) compared to placebo in endurance athletes. Your body doesn't read studies—it needs the whole team.

I've been using Thorne's Magnesium Bisglycinate with clients for years because their third-party testing is rigorous. Each capsule has 135mg elemental magnesium from 1,000mg magnesium bisglycinate. For someone with frequent cramps, I might recommend two capsules daily (270mg total).

Who Should Be Cautious or Avoid

Look, magnesium is generally safe, but there are exceptions:

• Kidney impairment: If you have reduced kidney function, magnesium excretion is impaired. The upper limit for supplemental magnesium is 350mg/day for adults, but with kidney issues, even that might be too much.
• Certain medications: Magnesium can interfere with absorption of some antibiotics (tetracyclines, quinolones) and bisphosphonates. Take them 2-4 hours apart.
• GI sensitivity: While glycinate is gentle, some people still experience loose stools. Start low (100mg) and increase gradually.
• Hypotension: Magnesium can lower blood pressure slightly. If you already have low BP or take antihypertensives, monitor.

I had a 58-year-old triathlete with stage 3 kidney disease—his nephrologist had him on a magnesium-restricted diet despite his cramps. We worked with his doctor to allow 100mg of glycinate daily, which helped without risking accumulation. Always check with your healthcare provider if you have medical conditions.

FAQs: Quick Answers

Q: Can I just take magnesium when I feel a cramp coming on?
No—magnesium doesn't work like that. It's not a rescue medication. It needs to be taken consistently to maintain adequate tissue levels. Acute cramp relief comes from stretching and sometimes sodium.

Q: Is magnesium citrate better for cramps since it's more "absorbable"?
Citrate has good absorption but acts as an osmotic agent in the gut. For many athletes, it causes diarrhea, especially at higher doses. Glycinate provides better absorption without the GI issues.

Q: How long until I see results for cramp prevention?
Most athletes notice improvement within 2-4 weeks if magnesium deficiency was contributing. But if you're not deficient, you might not see any change—that's why testing or a trial period makes sense.

Q: Can I overdo magnesium from supplements?
From food, virtually impossible. From supplements, yes—doses above 350mg/day can cause diarrhea initially, and chronic very high doses (1000mg+) can lead to toxicity, especially with kidney issues.

Bottom Line: What Actually Works

• Most exercise-associated cramps involve magnesium imbalance, not just potassium or dehydration.
• Magnesium glycinate at 200-400mg daily helps athletes with low intake or high losses—but won't help if you're already sufficient.
• Combine with sodium and potassium during endurance events for best prevention.
• Give it 2-4 weeks consistently—this isn't an acute fix.

Disclaimer: This is general information, not medical advice. Talk to your doctor before starting any supplement regimen, especially if you have health conditions.