Running 19 – Cramps while running: not necessarily from lack of salt

The climb onto the bridge at kilometer 36, the sun just rising over the row of tin roofs across the river. You are running at an even pace when the back of your left thigh locks up, as if someone had yanked hard on a cord. Your leg stops mid-stride and the knee will not straighten anymore. You hobble over to the railing. A passing runner holds out a salt tablet: “You’re low on salt, suck on this.” Since the start, you have taken one every hour. Two races ago, you also cramped on this very climb, in this very leg.

Sweat is salty, so everyone thinks of low salt straight away. Yet studies that follow long-distance runners find cramps going along with two things: the muscle has carried a load for too long, and the runner has had cramps before. The explanation most often given is that the nervous system controlling that muscle starts to fall out of rhythm.

The same climb, the same leg

At the 161 km ultra (a race longer than a marathon) that Hoffman and colleagues followed in 2015, 14.3 % of runners had true cramps, and another 26.8 % felt a muscle about to cramp. Two things went along with cramping: a past history of cramps, and a higher post-race level of the muscle enzyme CK (a blood marker that rises when muscle is damaged). How much weight runners lost, whether or not they used sodium tablets, and their blood sodium level were not related.

Pooling nine studies with 11,274 people, Costa and colleagues (2026) found that a past history was the link with the strongest evidence: people who had cramped during exercise before were about 4.4 times as likely to cramp again as people who never had (the figure is an odds ratio, a statistical way of comparing the likelihood between two groups). Age, weight and height were not related. Blood potassium and magnesium after the race were actually higher in those who cramped, not lower (moderate evidence for potassium, limited for magnesium). For hydration, electrolytes and training volume, each study found something different.

That is why Miller and colleagues (2022) class exercise-associated muscle cramps as caused by many factors. The data do not yet support treating loss of fluid or electrolytes as the main cause, and prevention has to be worked out for each person, not just by drinking more water. As for the magnesium tablets often passed around in running groups, the Cochrane review (a pooled, appraised summary of studies done to an international standard) by Garrison and colleagues (2020) found no randomized trial at all for exercise-associated cramps.

Heat cramps are different. Harrison’s textbook of internal medicine describes this type in people who sweat very heavily but drink only plain water (p. 3390), and that is when a sodium-containing drink in a long race in hot weather really helps. Its mechanism is still unclear, and Joyce and Lewindon (2016) lean toward ions not being moved well enough between the inside and the outside of cells, rather than too little in the diet or loss in sweat (p. 416).

An accelerator and a brake in one muscle

Walther, in the core textbook of Applied Kinesiology (AK, a method of testing muscle strength by hand to read the state of the body), uses arm wrestling as an example. A match often ends when one side suddenly gives way completely, the moment the inhibitory signal from the Golgi tendon organ (a sensor of tension located where muscle joins tendon) overrides the motor signal and switches the muscle off (Synopsis, p. 64). The muscle spindle (neuromuscular spindle cell, a sensor of length located within the muscle fibers), on the whole, drives that same muscle to contract (p. 62).

At the clinic we often compare the spindle to the accelerator and the Golgi organ to the brake. A cramp is like the accelerator still being pressed while the brake fails, so the muscle contracts hard and will not let go by itself. That picture fits what research has found, but it is still an explanation, not a measurement.

Right there by the railing

While the muscle is cramping, stop, stretch that same muscle passively, and hold still until it lets go (Miller and colleagues, 2022; Joyce and Lewindon, 2016). You can do it yourself:

• Back of the thigh cramping: sit down, straighten the leg, pull your toes toward you, and hold still;
• Calf cramping: straighten the knee and pull your toes toward your shin, or hold the railing and press your heel down to the ground;
• If someone is with you, ask them to support your leg and lengthen the muscle slowly, without jerking.

The salt tablet the passing runner held out cannot replace that movement.

For drinks that stop a cramp, the evidence is still small. Drinking a substance that stimulates TRP channels (a type of sensor in the mouth and throat that detects spicy, hot and cool tastes) beforehand let the muscle contract for longer before it cramped, in 39 people (Craighead and colleagues, 2017). Pickle juice reduced the pain of cramps, but in people with cirrhosis of the liver (Tapper and colleagues, 2022).

When cramps come with other signs

Sometimes a cramp is a sign of something else:

• With vomiting, diarrhea or dehydration during a race: take the person to medical staff, replace electrolytes first, and think about medicines later;
• Nausea, headache or confusion after drinking a lot: think of hyponatremia (sodium in the blood falling too low), and do not give more water;
• Urine as dark as cola, severe muscle swelling and pain, passing little urine after a long stage: this may be rhabdomyolysis (widespread damage to muscle tissue), and muscle enzymes and kidney function need testing.

If cramps keep coming back race after race, or every night after a long run, see a doctor to rule out electrolyte disorders, medicines you are taking (diuretics, or statins, which lower blood fats), nerve disease and venous insufficiency.

Strong when tested once, weak when tested many times

Goodheart once examined a downhill skier who could not hold the tucked position at the end of a run. Testing each leg and pelvic muscle one by one, every muscle was unusually strong. So he tested the way that person skied, one muscle tested several times in a row, and after only a few repetitions the hamstrings became clearly weak. AK’s repeated muscle testing comes from that case. Walther notes cramps at the end of a day of skiing or water-skiing as a sign of exactly this kind of disturbance (Synopsis, p. 187–188).

The week after the race, you lie face down on the examination table, knees slightly bent. The doctor tests your left hamstrings once, and the leg holds firm. Then the doctor tests them repeatedly, at a steady rhythm, and before the round is over the leg is drifting down toward the table. Tested once, it is strong, but when it has to work for a long time, your left hamstring group works below threshold (inhibited muscle), meaning it weakens on muscle testing, just as it did on the bridge climb.

The next job is to find out why. In the skiing case, when the patient placed a hand on the muscle’s neurolymphatic or neurovascular reflex points (points on the skin that AK finds are linked to each muscle), the repeated test no longer weakened. AK calls that self-placed touch therapy localization, and Goodheart believed that the fluid around the muscle was not carrying waste away and bringing nutrients in fast enough. Whichever point stops the muscle from failing, the doctor stimulates that reflex point (p. 188), then repeats the testing once more.

People prone to cramps sometimes cramp right on the examination table, and Walther explains how to hold the hamstrings so they do not cramp during testing (p. 311). Next to that muscle group, he notes that when there are cramps one should think of betaine HCl (a supplement that adds acid to the stomach) or another calcium need. Cuthbert also leans toward calcium: cramps at night, after exercise or right during muscle testing are a sign that the whole body needs further assessment, most likely calcium metabolism (p. 157). These are things to test on your own body, not a shopping list.

Four muscle quadrants, four ions

In the Winter 1983 proceedings of the International College of Applied Kinesiology (ICAK), Schmitt divided the large muscles around the spine and pelvis into four quadrants. Calcium belongs to the right flexor quadrant, sodium to the left flexor quadrant, potassium to the right extensor quadrant and magnesium to the left extensor quadrant (p. 176). “Flexor” means the muscles that contract when you bend forward or flex the hip; “extensor” means the muscles that contract when you arch back or extend the hip. Calcium and sodium go with muscle contraction, potassium and magnesium with muscle relaxation (p. 179–181). A muscle that is still weak after treatment often strengthens when the patient holds the ion of its quadrant on the tongue (p. 184).

Your left hamstrings sit in the left extensor quadrant, so the doctor has you hold a little magnesium on your tongue and then repeats the testing. When one ion is replaced and that muscle strengthens, often a muscle in another quadrant that was strong turns weak, waiting for a second ion. Schmitt writes that one ion revealing the need for another is “the rule rather than the exception” (p. 185). Maffetone, in the same proceedings, describes a runner whose gait gradually went off after a few miles: holding calcium on the tongue changed nothing, magnesium changed it a little, and both together changed the running gait clearly. AK, he reminds us, looks at the whole person rather than looking for one nutrient to stamp out one muscle imbalance (p. 113).

Sodium, the target of “you’re low on salt,” is only one of the four quadrants. A muscle strengthening with magnesium on the tongue does not erase what the Cochrane review found, either. For us, it is a hint specific to you, to be set beside your daily diet and lab tests when needed. Doses are not set by muscle testing.

The calf has its own story. Night-time calf cramps, according to Cuthbert, may come from trigger points (tight knots in the muscle that hurt when pressed) in the gastrocnemius muscle, or from imbalances of vitamins (especially B2, B3, B6) and minerals (especially potassium) (p. 15). The soleus (a muscle lying deep under the gastrocnemius) tends to be tight rather than weak, and a tight soleus can cause cramps, along with numbness in the sole of the foot after jumping or running (Garten, Muscle Test Handbook, p. 222).

Peony and licorice for undernourished sinews

Older people in Vietnamese families call a cramp “rut gan”, the sinew pulling. That word for sinew is close to the sinews (jin, 筋) of traditional medicine, and traditional medicine says the Liver governs the sinews (肝主筋, gān zhǔ jīn), meaning the Liver organ system oversees the tendons and muscles (Basic Theory of Chinese Medicine, 中医基础理论 / 中醫基礎理論, p. 219). People who often get calf cramps at night or after a long run, with numb legs, pale nails and lips, and, in women, scanty periods, may fit the pattern of Liver blood deficiency with the sinews undernourished (肝血虚、筋失养 / 肝血虛、筋失養, gān xuè xū, jīn shī yǎng): the blood is not enough to nourish the sinews. We set this view alongside “neuromuscular fatigue” and do not treat blood deficiency as the physiological explanation of the cramp.

The base formula is Shao Yao Gan Cao Tang (芍药甘草汤 / 芍藥甘草湯, Peony and Licorice Decoction) from the Shang Han Lun (伤寒论 / 傷寒論, Treatise on Cold Damage), with 12 g each of Bai shao (Paeonia lactiflora root, white peony) and Zhi gan cao (honey-fried Glycyrrhiza uralensis root, licorice). The old physicians explained it with four characters, “sour and sweet transform into yin” (酸甘化阴 / 酸甘化陰, suān gān huà yīn): the sour taste of peony meets the sweet taste of licorice and generates yin, which nourishes the sinews. For painful calf spasms, add Niu xi (Achyranthes bidentata root), Mu gua (Chaenomeles speciosa fruit) and Yi yi ren (Coix lacryma-jobi seed) (Vernacular Explanations of Chinese Medicine Verses, 中医歌诀白话解丛书 / 中醫歌訣白話解叢書, p. 1177–1179). For the Liver blood deficiency pattern, the formula is often combined with Si Wu Tang (四物汤 / 四物湯, Four Substances Decoction), following the combination in Bu Gan Tang (补肝汤 / 補肝湯, Liver-Supplementing Decoction) (Formulas of Chinese Medicine, 方剂学 / 方劑學, p. 184).

The Kampo granule form (traditional herbal medicine in the Japanese style, code TJ-68) has data in two groups. In people on dialysis, 54 of 61 had their cramps stop within about five minutes; the study had no control group, that is, no group of people not taking the medicine for comparison (Hyodo and colleagues, 2006). In people with lumbar spinal stenosis, the randomized comparison of 30 people found 13 of 16 had at least half as many cramps, compared with 4 of 14 in the group taking the muscle relaxant eperisone (Takao and colleagues, 2015). There is no trial yet for exercise-associated cramps. For runners, the formula rests on the classical texts and on recorded case series.

Licorice must be kept to a limited dose. At large doses or over long periods, about one in five people develop swelling, weak limbs, muscle stiffness, numbness, dizziness, high blood pressure or low potassium (Chinese Materia Medica, Advanced Series, 中药学 / 中藥學, p. 1637–1638). Low potassium in turn weakens muscles and makes stiffness worse, so overdoing it turns the very herb used to ease cramps against you. We keep total Gan cao at no more than 2 g a day, much lower than in the original formula, and only use the name “modified Shao Yao Gan Cao Tang” when the prescription keeps the ratio of four parts Bai shao to one part Gan cao. People with high blood pressure, heart disease, kidney disease or low potassium, or who are taking diuretics, digoxin (a heart medicine) or corticosteroids, should not take Gan cao. Women who are pregnant or trying to conceive should not take Niu xi, Yi yi ren, Chuan xiong (Ligusticum chuanxiong rhizome) or Gan cao. If you are running a race with doping control, tell us beforehand: Suan zao ren (Ziziphus jujuba var. spinosa seed) in the original Bu Gan Tang is one of nine herbs that contain higenamine (a substance on the prohibited doping list), and there is no substitute for it yet, so the medicine must be taken at least 1 day apart from race day.

Once the causes in the section above have been ruled out, the doctor may prescribe a decoction in ready-to-drink 50 ml pouches, matched to your pattern, for the weeks between races. A cramp in the middle of a race still depends on stretching.

A small notebook for the bridge climb

That evening, you write a few lines in a notebook: kilometer 36, left hamstrings, third time, already sunny, had taken five salt tablets. A history of cramping is the strongest warning sign research has found, so those few lines tell the doctor which muscle to test first. Next year’s race still crosses that bridge.

If you keep cramping in the same spot over two or three races, or cramp at night after every long run, make an appointment with Dr. Dinh Ngoc Duc (MD, MSc in Traditional Medicine). The visit will test the very muscle group that cramped, once and then many times in a row, before any talk of supplements or herbal decoctions. Book a consultation.

Worth keeping

• If a cramp hits mid-run, stop and slowly stretch the cramping muscle, holding until it lets go;
• Salt tablets may not prevent cramps while running, and magnesium tablets have no trial at all for this type of cramp;
• Cramps with vomiting, diarrhea, confusion, or urine as dark as cola: get medical care right away;
• Nausea, headache or confusion after drinking a lot: do not drink more water;
• Record each cramp: the kilometer, which leg, the weather, what you ate and drank;
• Cramps that recur over many races or at night: see a doctor to find the cause;
• Add up every source of licorice, including teas and lozenges, and keep it to no more than 2 g a day.

References

Sources in English

• Costa LDS, Correa VAF, de Oliveira VF, Jahn AJS, Aliano GB, Nunes GS. 2026. Risk Factors for Exercise-Associated Muscle Cramps: A Systematic Review With Meta-Analysis. Muscle Nerve. 74(5):1375-1386. doi:10.1002/mus.70389. PMID: 42693659.
• Craighead DH, Shank SW, Gottschall JS, Passe DH, Murray B, Alexander LM, et al. 2017. Ingestion of transient receptor potential channel agonists attenuates exercise-induced muscle cramps. Muscle Nerve. 56(3):379-385. doi:10.1002/mus.25611. PMID: 28192854.
• Cuthbert S. 2013. Applied Kinesiology: Clinical Techniques for Lower Body Dysfunctions. Gangasas. p. 15, 157.
• Garrison SR, Korownyk CS, Kolber MR, Allan GM, Musini VM, Sekhon RK, et al. 2020. Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev. 9(9):CD009402. doi:10.1002/14651858.CD009402.pub3. PMID: 32956536.
• Garten H. 2013. The Muscle Test Handbook: Functional Assessment, Myofascial Trigger Points and Meridian Relationships. Edinburgh: Churchill Livingstone Elsevier. p. 222.
• Hoffman MD, Stuempfle KJ. 2015. Muscle Cramping During a 161-km Ultramarathon: Comparison of Characteristics of Those With and Without Cramping. Sports Med Open. 1(1):24. doi:10.1186/s40798-015-0019-7. PMID: 26284165.
• Hyodo T, Taira T, Takemura T, Yamamoto S, Tsuchida M, Yoshida K, et al. 2006. Immediate effect of Shakuyaku-kanzo-to on muscle cramp in hemodialysis patients. Nephron Clin Pract. 104(1):c28-32. doi:10.1159/000093256. PMID: 16685141.
• Jameson JL, Fauci AS, Kasper DL, Hauser SL, Longo DL, Loscalzo J, editors. 2018. Harrison’s Principles of Internal Medicine. 20th ed. New York: McGraw-Hill Education. p. 3390.
• Joyce D, Lewindon D, editors. 2016. Sports Injury Prevention and Rehabilitation: Integrating Medicine and Science for Performance Solutions. London: Routledge. p. 416.
• Maffetone P. 1983. Preliminary Observations. ICAK Collected Papers, Winter 1983. p. 111–113.
• Miller KC, McDermott BP, Yeargin SW, Fiol A, Schwellnus MP. 2022. An Evidence-Based Review of the Pathophysiology, Treatment, and Prevention of Exercise-Associated Muscle Cramps. J Athl Train. 57(1):5-15. doi:10.4085/1062-6050-0696.20. PMID: 34185846.
• Schmitt WH. 1983. Body Quadrants and the Cations. ICAK Collected Papers, Winter 1983. p. 176–185.
• Takao Y, Takaoka Y, Sugano A, Sato H, Motoyama Y, Ohta M, et al. 2015. Shakuyaku-kanzo-to (Shao-Yao-Gan-Cao-Tang) as Treatment of Painful Muscle Cramps in Patients with Lumbar Spinal Stenosis and Its Minimum Effective Dose. Kobe J Med Sci. 61(5):E132-7. PMID: 27363396.
• Tapper EB, Salim N, Baki J, Zhao Z, Sundaram V, Patwardhan V, et al. 2022. Pickle Juice Intervention for Cirrhotic Cramps Reduction: The PICCLES Randomized Controlled Trial. Am J Gastroenterol. 117(6):895-901. doi:10.14309/ajg.0000000000001781. PMID: 35416793.
• Walther DS. 2000. Applied Kinesiology: Synopsis. 2nd ed. Pueblo (CO): Systems DC. p. 62–64, 187–188, 311.

Sources in Chinese

• 高学敏, 主编. 中医药学高级丛书 · 中药学. 第 1637–1638 页.
• 李冀, 连建伟, 主编. 方剂学. 第 184 页.
• 王新华, 主编. 中医药学高级丛书 · 中医基础理论. 第 219 页.
• 中医歌诀白话解丛书. 第 1177–1179 页.