ASK THE SPORTS DIETITIAN Andrew Hall is an Accredited Practising Dietitian, sports dietitian and exercise scientist based in Brisbane. Andrew works with elite and sub-elite athletes across a wide range of sports, with particular interests in endurance athletes, team sports and strength/power-based sports. He has worked with Australian representatives and is also involved with the Gold Coast Suns Football Club.
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Q I often get muscle cramps when running, should I be taking a magnesium supplement?
Anyone who has suffered from a muscle cramp during or after exercise understands that it’s definitely something worth trying to avoid. For those who have been lucky enough to evade them, a muscle cramp is a sudden, involuntary, painful contraction of a muscle. These symptoms generally ease off within seconds to minutes, but are often accompanied by a palpable knotting of the muscle. While magnesium does play many important roles in the body, unfortunately the prevention/reduction of exercise-induced muscle cramps is not one of these. It is easy to be confused considering the heavy marketing for magnesium supplements and the prevention of cramps, but to date the scientific research suggests that there is no strong link between exercise-induced muscle cramps and magnesium supplementation.
While oral magnesium does not appear to have any beneficial effects in athletes with adequate magnesium, supplementation may improve performance in individuals with a diagnosed deficiency. Those undertaking a high volume chronic training load (e.g. long distance runners) or those with a restricted energy intake may be at risk of magnesium deficiency, although this is not common and you should always get this checked out with your GP before supplementation. It is worthwhile noting that the intestinal absorption of magnesium varies depending on how much magnesium the body needs. If there is too much magnesium, the body will only absorb as much as it needs. So how much do I need? I hear you ask. The recommendations suggest that adults consume a range between 350 and 400 mg/day as the upper limit. Most individuals who are eating a healthy well balanced diet will be acquiring the required amount of magnesium through wholefoods. Good food sources of magnesium include vegetables, legumes, fish, nuts and whole grains. For example, 30g of brazil nuts provides about 100mg, and ½ cup cooked quinoa provides about 50mg of magnesium.
Ok, so what does cause cramps and what can I do to avoid them?
What we do know about cramps is that the main risk factors include; family history of cramping, previous occurrence of cramps during or after exercise, increased exercise intensity and duration, and inadequate conditioning for the activity. This explains the classic example of cramping on race day. During a race you’re typically working at a higher intensity than normal, and often over a longer duration than during training.
From a nutrition perspective, glycogen depletion (insufficient carbohydrate) or low energy availability can also contribute to fatigue and therefore cramping. This highlights the importance of getting your nutrition and fuelling plans for long sessions and races spot on.
The bottom line is, if you suffer from regular muscle cramps during exercise or you are concerned about your magnesium intake, an Accredited Sports Dietitian (AccSD) can analyse your diet and help you meet your requirements for training and overall health and wellbeing. Find an Accredited Sports Dietitian at Sports Dietitians Australia.
