The Role of Magnesium and Potassium in Athletic Performance
Magnesium and potassium are two minerals often overlooked by athletes, yet frequently the cause of cramps, fatigue, and declining performance. Discover what science says about the role of these electrolytes.
Written by
João Araújo
Physical Education Teacher (FADEUP – University of Porto) · Futsal Coach – Level II · UEFA B License · Master’s in Physical Education
15 years teaching Physical Education in schools, 20 years coaching futsal at youth development level and 5 years coaching football. Federated and amateur football and futsal player.
A cramp in the 85th minute of a match. Inexplicable fatigue in the third kilometre of a run that should have been easy. Muscle contractures after a week of intense training. These situations are often interpreted as lack of fitness or insufficient training. Frequently, the cause is simpler and more correctable: a deficiency of magnesium or potassium.
Magnesium: The Mineral of 300 Processes
Magnesium is a cofactor in more than 300 enzymatic reactions in the human body. For athletes, the most relevant are:
ATP Production: magnesium is essential for the synthesis of adenosine triphosphate (ATP), the cellular energy currency. Without sufficient magnesium, the efficiency of energy production decreases, resulting in earlier fatigue and a reduced capacity to sustain intense efforts.
Muscle Protein Synthesis: magnesium participates in the activation of enzymes necessary for protein synthesis, the central process of muscle repair and growth after training.
Intracellular Calcium Regulation: magnesium and calcium function as antagonists in muscle contraction. Calcium triggers contraction; magnesium facilitates relaxation. A magnesium deficiency results in a state of muscular hyperexcitability, clinically manifested as cramps, spasms, and contractures.
Sleep Quality: magnesium activates GABA receptors (gamma-aminobutyric acid), the primary inhibitory neurotransmitter in the central nervous system. Low magnesium levels are associated with lighter and poorer-quality sleep, compromising the athlete’s recovery.
Requirements and Deficiency
The recommended daily intake ranges from 310–420 mg/day for adults. Athletes with high training volumes who sweat abundantly may have needs 10–20% higher, since sweat eliminates magnesium significantly.
Foods rich in magnesium: pumpkin seeds, spinach, almonds, black beans, dark chocolate (70%+), oats.
Signs of deficiency: frequent muscle cramps, irritability, chronic fatigue, insomnia, palpitations.
Potassium: The Guardian of Action Potential
Potassium is the main intracellular cation of the human body. Most of the body’s potassium is inside cells, in contrast to sodium, which predominates in the extracellular space.
This distribution is fundamental to muscle and nerve action potential: the concentration difference between intracellular potassium and extracellular sodium creates the electrochemical gradient necessary for the transmission of nerve signals and muscle contraction.
During intense exercise, potassium leaves muscle cells and moves into the extracellular space, contributing to peripheral muscle fatigue. A muscle that is adequately replenished with potassium recovers this gradient more quickly, translating into shorter recovery time between repeated efforts.
In the cardiovascular system, potassium regulates heart rate and blood pressure. Endurance athletes deficient in potassium show a higher risk of cardiac arrhythmias during prolonged efforts.
Requirements and Deficiency
The recommended daily intake is approximately 3500–4700 mg/day. High-intensity athletes who sweat abundantly can lose 200–400 mg of potassium per hour of exercise.
Foods rich in potassium: banana (362 mg/100g), baked sweet potato (475 mg/100g), avocado, white beans, yoghurt, salmon.
Signs of deficiency (hypokalaemia): muscle cramps, weakness, fatigue, palpitations, constipation.
The Interaction Between Magnesium and Potassium
Magnesium and potassium have a direct physiological relationship: magnesium is necessary to keep potassium inside cells. In magnesium deficiency, the body loses potassium regardless of intake. This explains why isolated potassium supplementation may be ineffective when magnesium is lacking.
For athletes with frequent cramps, the most effective approach is to check and correct magnesium status first, before moving on to potassium supplementation.
Supplementation: When and How
Magnesium supplementation has solid scientific evidence for athletes with confirmed deficiency or high training volume. Forms with the best absorption:
- Magnesium malate: good absorption, fewer gastrointestinal side effects
- Magnesium citrate: good absorption, widely available
- Magnesium glycinate: excellent absorption, recommended for sleep disorders
Typical dose: 200–400 mg/day, preferably at night (due to its relaxing effect).
For potassium, supplementation at high doses requires medical supervision. The nutritional approach through food is generally sufficient and safer.
Magnesium and potassium losses accelerate with your sweat rate, so hydration status directly affects your mineral balance. Learn how to calculate your own fluid loss during training to keep both water and electrolytes in check.
The minerals we ignore are often the ones our body needs most.