Magnesium and endurance: a deficit more common than you think
You finish a long 90-km ride, your legs are burning, sleep comes in fragments and the next morning a violent cramp wakes you up. That triad — cramps, persistent fatigue, broken nights — is the classic signature of inadequate magnesium status in endurance athletes. It is no coincidence: sweat continuously exports magnesium, and the heavier the training load, the deeper the deficit grows. Recent data put the daily requirement at 300-400 mg for sedentary adults, but athletes can significantly exceed that threshold.
The key is not just to supplement, but to choose the right form. And not all forms are equal — not by a long way.
Ograal tracks your magnesium status every week
Ograal integrates weekly micronutrient tracking (magnesium, iron, calcium, vitamins) directly into its automatic meal plan. The app detects potential deficiencies based on your training volume and adjusts meals accordingly — with a Daily Insight, one of 30+ daily nutritional rules, to guide you without overwhelming you.
Five forms of magnesium: which one to choose for endurance?
The market is saturated with supplements, but the formulas vary enormously. Here is a concise comparison of the five most common forms:
Bisglycinate stands out on two counts: its bioavailability is superior (glycine facilitates active transport across the intestinal wall) and its digestive tolerance is excellent, even at high doses. That matters when you train early in the morning or the day before a target race.
Why citrate is problematic before a long training day
Magnesium citrate is often praised for its good bioavailability, but its osmotic effect accelerates intestinal transit. For a runner who wakes at 5:30 am before a half-marathon or a long run, a nighttime dose of citrate can cause urgent bathroom stops at kilometre 8. This is not anecdotal: studies on mineral supplementation in athletes consistently document this limitation.
Bisglycinate carries no such risk — which is one of the main reasons it has become the reference in precision sports nutrition.
Sweat loss: 150 mg extra per 1,000 kcal expended
A cyclist or runner who expends 1,000 kcal during an intense session loses on average 150 mg of additional magnesium above their basal requirement. Over a training week of three to five sessions, the cumulative deficit can reach 600-900 mg — equivalent to two or three days of recommended intake sweated away. Diet alone, however well structured, struggles to compensate without a targeted strategy.
When to take bisglycinate: the post-training and evening combination
Timing matters. Two windows are particularly effective:
- Post-training with the recovery meal — magnesium accompanies carbohydrates and proteins in the anabolic window, supporting glycogen resynthesis and reducing muscle inflammation.
- Evening dose 30-60 minutes before bed — magnesium potentiates deep sleep (delta waves), during which most tissue repair occurs.
Avoid taking it on an empty stomach in the morning, which is less well tolerated. Split doses above 150 mg at a time to maximise absorption. The effective dose for an endurance athlete generally sits between 300 and 400 mg/day of elemental magnesium.
Dual benefit: cramps and sleep quality
Magnesium acts on two complementary levels. First, muscle contraction: it blocks calcium channels at neuromuscular junctions, reducing the hyperexcitability responsible for nocturnal cramps and exercise contractures. Second, the central nervous system: it modulates NMDA and GABA receptors, facilitating the transition into deep slow-wave sleep.
Studies on magnesium supplementation and sleep quality consistently show improvements in deep sleep duration and fewer nocturnal awakenings, translating into measurable recovery outcomes — lower resting heart rate and improved heart rate variability on waking. For endurance athletes, that is where long-term progress is built.
Foods naturally rich in magnesium
Supplementation is a complement, not a replacement for a well-structured diet. The best dietary sources of magnesium include:
- Pumpkin seeds (156 mg/30 g) — scatter on morning porridge
- Dark chocolate ≥ 70% (64 mg/30 g) — the post-session square is more than just a treat
- Almonds (76 mg/30 g) — a practical pre- or post-training snack
- Cooked spinach (78 mg/100 g) — integrate into the recovery dinner
- Legumes: lentils, chickpeas (around 50 mg/100 g cooked)
- Magnesium-rich mineral waters (Hépar: 110 mg/L, Contrex: 84 mg/L)
Even with these foods, an athlete training 8-12 hours per week can easily exceed dietary magnesium capacity. That is exactly where bisglycinate works as a precision lever.
What the research says
The meta-analysis by Tarsitano et al. (2024) on the effects of magnesium supplementation on muscle soreness concluded that athletes engaged in intense exercise have magnesium requirements 10-20% higher than sedentary individuals, and that taking capsules 2 hours before training reduces muscle damage and improves recovery.
The review by Xun et al. (2017) in Nutrients documents how magnesium improves glucose availability in muscle and brain during exercise, reduces lactate accumulation, and supports endurance performance — with a particularly strong signal in deficient subjects.
Finally, Domínguez et al. (2025) confirm that athletes constitute a high-risk population for magnesium deficiency, directly linked to sweat losses and metabolic training stress. The authors highlight the interaction between magnesium and vitamin D, two micronutrients that are often deficient together in endurance athletes who train indoors during winter.
Recommended product
Chocolate Recovery Protein Drink 512g — Decathlon
A complete recovery drink (protein + carbohydrates) to consume in the post-exercise window, ideal alongside magnesium bisglycinate supplementation.
Key takeaways
- Choose bisglycinate: superior bioavailability, no laxative effect.
- Account for sweat losses: +150 mg per 1,000 kcal expended in intensive exercise.
- Double timing: post-training + 30-60 minutes before bed.
- Effective dose: 300-400 mg/day of elemental magnesium for endurance athletes.
- Combine diet and supplementation: pumpkin seeds, almonds, spinach, dark chocolate.
- Use Ograal for automated long-term micronutrient tracking.
Sources
[1] Xun P. et al., "Can Magnesium Enhance Exercise Performance?", Nutrients, 2017. https://doi.org/10.3390/nu9090946
[2] Tarsitano M.G. et al., "Effects of magnesium supplementation on muscle soreness", J Transl Med, 2024. https://doi.org/10.1186/s12967-024-05434-x
[3] Domínguez L.J. et al., "The Importance of Vitamin D and Magnesium in Athletes", Nutrients, 2025. https://doi.org/10.3390/nu17101655
[4] Heffernan S.M. et al., "The Role of Mineral and Trace Element Supplementation in Exercise", Nutrients, 2019. https://doi.org/10.3390/nu11030696
