Heavy exercise can cause painful muscle cramps but there are some solutions worth considering.
Question: I periodically get signs of cramp while, or after, clearing trap lines, which takes at least four hours of bushwalking in hilly terrain. Experimenting with salt-water drinks has shown benefits in ending them. Of course, it’s not science, but I shall continue the trial.
Answer: Exercise-associated muscle cramps are relatively common, with a study reporting they occurred in about 39% of marathon runners, 52% of rugby players, 60% of cyclists, and a sizeable 68% of triathletes.
Cramps also afflict more than a few Listener readers, judging by the emails following our column on night cramps (A complex problem, April 15). The column suggested trialling a vitamin B complex supplement for night-time leg cramps in older adults (see reader question, opposite).
However, cramps that occur alongside heavy or prolonged exercise, along with potential dehydration, require a different solution.
Although water is essential for hydration, drinking too much plain water during exercise can negatively affect performance. So-called over-hydration during ultra-marathons, for example, is the primary characteristic of hyponatremia, which causes painful muscle cramps. Individuals with the condition have abnormally low sodium levels in their blood, which is problematic as sodium regulates the amount of water in and around body cells.
Drinking too much water during exercise may dilute the sodium and other electrolytes in the body, increasing the risk of muscle cramps. Indeed, researchers have found that marathon runners who experience them during an event have significantly lower blood sodium levels than other runners.
Oral rehydration solutions (ORS) treat or prevent dehydration and contain much higher sodium and potassium levels than a regular sports drink.
In findings published in the Journal of the International Society of Sports Nutrition in 2021, researchers found that ingesting an ORS during exercise reduced susceptibility to exercise-associated muscle cramps. The ORS used in this study contained glucose and electrolytes such as sodium, potassium, magnesium and chloride.
During the clinical trial, the men completed a downhill run for 40-60 minutes covering about 8km in a hot environment (35-36°C). The participants ran twice on separate occasions, once using plain spring water for hydration and the second time using the ORS. They then had electrical stimulation applied to their calf muscles to induce cramps, which revealed those drinking the ORS were less susceptible to them.
More research is needed – for instance, we do not know exactly which electrolytes or other ingredients are responsible for this effect yet. Nevertheless, if you wish to trial an ORS with similar nutrition parameters, I have compiled nutrition data for the ORS and commonly available drinks in the table (opposite page). However, if you have kidney disease, are taking heart or blood pressure medicine, or are pregnant, please discuss it with your doctor before trialling a product like this.
Question: Thank you for your article on cramps (April 15). However, should the recommended dose of a vitamin B complex be 500mg daily rather than the 50mg mentioned?
Answer: The 2023 review highlighted in my previous column recommended trialling a vitamin B complex supplement for night-time cramps. That recommendation was based on a clinical trial published in 1998 that found 86% of older patients taking a vitamin B-complex supplement had significant remission of their nocturnal leg cramps.
The supplement used in the clinical trial contained 50mg of vitamin B1 (thiamine), 5mg of vitamin B2 (riboflavin), 30mg of B6 and 250mcg of B12. Thus, around 85.25mg of various B vitamins overall.
However, most B complex supplements on the market contain considerably higher doses – which may be why you’ve queried the amount.
Notably, there are no upper recommended limits of safe intake for vitamins B1, B2 and B12, as there are no recorded adverse events from higher intake of them. Vitamin B6 has a recommended intake upper limit of 50mg a day – excessive amounts can cause nerve damage – so ensure your total intake of B6 from food and supplements does not exceed that.
