In a high-endurance physical activity like a marathon, we are well aware of the importance of the key nutrients such as carbohydrates, proteins, fats, vitamins and minerals, which is quite appreciable. However, have you missed out on something very important? Yes. They are salts. Your sweat consists of both water and salts. These salts, also known as electrolytes, are essential for maintaining balance in your body’s cells.
During a marathon, the average sweat loss rates may vary between 0.5 to 1.5 L of fluid loss every hour and can be even higher depending on the individual and climatic conditions.1
Exercising moderately in cool or temperate conditions
Racing in hot conditions
500 mL or 1 standard water bottle per hour
1 L or 2 standard water bottles per hour
Electrolytes and their importance
Electrolytes such as sodium, potassium and magnesium regulate your body functions. Electrolytes that are lost through sweat should be replenished from time to time to maintain optimal performance during the run.
Electrolyte imbalance can result in muscle fatigue, cramps, fatigue, dizziness, nausea and constipation. Different electrolytes and their importance are described below.2-5
Sodium: Sodium helps the cells to retain water and prevent dehydration. It also has an important role in energy release. For events that last longer than 5 hours, hyponatraemia (low sodium levels) is an important concern as you tend to lose sodium through sweat.2
Runners should aim at getting 80 to 100 mg sodium per 32 ounces (950 mL) of hydrating beverage and 100 to 300 mg sodium per hour from other sources.2
Magnesium: Magnesium has a vital role in muscle relaxation, bone remineralisation and energy release. It also plays an important role in red blood cell production. Loss of magnesium can contribute to early fatigue, nausea and muscle cramps during the run.3,4
Recommended intake for endurance athletes is 500 to 800 mg daily3,4
Potassium: Potassium helps in regulating the water content in your body and stabilising muscular contraction. It enhances recovery and muscle hydration. Excess loss of potassium may result in fatigue.5
Potassium intake should be approximately 435 mg for 1 hour of exercise 5
Tips for salt loading
- Monitor your thirst levels and urine colour and learn to manage your input well.
- Ensure that you consume enough electrolyte-rich foods, sodium (table salt, meat, fish and pickles), potassium (fruits, vegetables, nuts and pulses) and magnesium (green leafy vegetables, nuts, legumes and eggs).
- Keep a quick snack or beverage ready with you during the run (energy bars and gels).
- For moderate fluid losses, a sports drink (10-25 mmol/L of sodium) is adequate. When fluid losses are high (>2 L), sodium intake of 50 to 80 mmol/L may be required.1,6-8
Every runner is different when it comes to losing and replenishing electrolytes.
Keeping your electrolyte levels balanced is the key for a successful finish.
- Baker A. Essentials of nutrition for sports. Washington DC, San Diego: Argo Publishing 1820; 2005.
- Hiller WD, O’Toole ML, Fortess EE, Laird RH, Imbert PC, Sisk TD. Medical and physiological considerations in triathlons. Am J Sports Med. Mar 1987;(2):164-7.
- Altura BM, Gebrewold A, Altura BT, Brautbar N. Magnesium depletion impairs myocardial carbohydrate and lipid metabolism and cardiac bioenergetics and raises myocardial calcium content in-vivo: relationship to etiology of cardiac diseases. Biochem Mol Biol Int. Dec 1996;40(6):1183-90.
- Seelig M. Magnesium deficiency in the pathogenesis of disease. New York: Plenum Press; 1980.
- Wenk C. Methodological studies of the estimation of loss of sodium, potassium, calcium and magnesium through the skin during a 10-km run. Schweiz Z Sportmed. Dec 1993;(4):301-7.
- Food and Agriculture Organization. Human vitamin and mineral requirements. Rome, Italy: FAO; 2001.
- Australian Institute of Sport. Current Concepts in Sports Nutrition. Bruce, Australia: Australian Institute of Sport; 2016.
- Australian Sport Commission. Electrolyte replacement supplements. Bruce, Australia: AIS Sports Nutrition; 2014.