Charley Horse: What Causes It and What Actually Helps
Table of Contents
Key Takeaways
- A charley horse is a sudden, involuntary, painful muscle cramp. In a primary care study of patients aged 60 and over, the calves were the main location in 80% of cases.[1]
- Two important clinical presentations are cramps at rest (often at night) and exercise-associated muscle cramps (EAMC); other cramps can be associated with medical conditions, medications or pregnancy.
- In athletes, a prospective Ironman cohort found no statistically significant differences in serum electrolyte or body-weight changes between athletes who cramped and those who did not; faster racing and a history of cramping were the independent risk factors.[2]
- A Cochrane review concluded that magnesium is unlikely to provide clinically meaningful prevention of cramps in older adults.[3]
- In a Cochrane review, quinine reduced the number of cramps (low-quality evidence), but because serious adverse events can rarely be fatal, its prescription is severely restricted in some countries.[4]
- In my clinical experience, many patients attribute their cramps to a lack of magnesium or other electrolytes, but in my view cramps are often not simply an electrolyte shortage; research points to several possible mechanisms, including altered neuromuscular control.
- In my practice, a calf that stays sore, or becomes “crampy” more often than usual, often prompts a calf ultrasound, and from time to time a venous thrombosis is found behind the symptoms.
- In my experience, some “cramps” turn out to be restless legs, sciatica, a muscle tear or even an Achilles tendon rupture.
- In my view, cramps or muscle twitches alone are not a reason to suspect ALS when there is no weakness, muscle wasting, other new symptoms or abnormal findings.
Introduction: Why the Charley Horse Is Still Poorly Understood
Many people have been woken at night by a calf that suddenly locks into a rock-hard, painful knot, or has felt a muscle seize late in a race. “Charley horse” is the everyday name for this kind of muscle cramp, and it is remarkably common: in a cross-sectional study of 516 primary care patients aged 60 and over, the adjusted prevalence of cramps was 46%.[1]
Despite how familiar it is, the charley horse is surprisingly poorly explained. A review in Sports Medicine concluded that no prevention strategy or treatment for exercise-associated cramps is consistently effective, and that different mechanisms likely operate in different situations.[5]
As both a physician and a former competitive athlete, I see charley horses from two directions: older patients whose sleep is disrupted by night cramps, and athletes who cramp under competitive load. This article covers what a charley horse is, how common it is, what the research says about its causes, and how well popular remedies such as magnesium, electrolytes, pickle juice and quinine hold up.
What Is a Charley Horse?
A charley horse is a muscle cramp: a sudden, involuntary and painful contraction of a muscle that can be felt as a hard knot.[1] The primary care study above described cramps as lasting from a few seconds to a few minutes and easing on their own.[1]
Researchers usually separate cramps into broad groups, because the triggers and the evidence differ:
- Rest (nocturnal) leg cramps: cramps that come on during rest, usually at night, and are most common in older adults. The study authors grouped these as idiopathic cramps.[1]
- Exercise-associated muscle cramps (EAMC): cramps occurring during or soon after physical activity.[5]
- Cramps linked to pregnancy, medical conditions or medications.[1]
This distinction matters because a charley horse at 3 a.m. in a 70-year-old and a calf cramp at kilometre 38 of a marathon may not share the same cause, and the treatment evidence for one does not automatically apply to the other.
How Common Are Charley Horses?
At rest and at night
In the French primary care study of 516 patients aged 60 and over, 31% of the whole sample reported being woken up by cramps, and 15% had cramps more than three times a month. For 58%, cramps had started five or more years earlier.[1] Only a minority of those affected had cramps more than once a week, but cramp-related sleep disturbance was common.[1]
In my clinical experience, cramps are not among the most frequent reasons patients come in, but they do come up from time to time. Many describe night-time calf cramps, although some have them during the day as well. Patients often attribute their cramps to a lack of magnesium or another electrolyte, and many tell me they are already taking magnesium to prevent them.
In athletes
Figures for exercise-associated cramps vary widely. The Sports Medicine review notes that comparing surveys is hampered by different definitions, measurement periods and assessment tools, and that published figures mix incidence in single events with lifetime incidence.[5] In a prospective Ironman cohort of 210 recruited triathletes, 43 reported cramps during or immediately after the race and were compared with 166 who did not.[2] The review also notes that, most often, cramping is a relatively minor inconvenience.[5]
What Causes a Charley Horse?
The two competing explanations
Two main hypotheses have dominated the debate: a disturbance of water and salt balance, and a neurological cause in which the nervous system keeps driving the affected muscle abnormally. The Sports Medicine review concluded that each has some support but that neither fully explains exercise-associated cramps, and that the evidence on both sides is weak.[5]
In the review’s words, some cramps appear to involve sustained abnormal spinal reflex activity secondary to fatigue of the affected muscles. The hypothesis it describes is that fatigue increases excitatory signalling from muscle spindles and reduces inhibitory feedback from Golgi tendon organs, leading to sustained activation of the motor neurons supplying the muscle.[5]
Is dehydration to blame?
The Sports Medicine review argues that the salt-and-water explanation may have more support than is often acknowledged. It notes that this evidence comes largely from medical records in large industrial settings, supported by one large-scale intervention trial, and concludes that in occupational settings involving hard physical effort, high ambient temperature and large sweat losses with large volumes of plain water may be risk factors, with some evidence that adding salt to fluids reduces the risk.[5] These were occupational settings rather than sport.
In athletes, prospective data point elsewhere. In a cohort of 210 Ironman triathletes, the 43 who cramped did not differ significantly from the 166 who did not in pre- to post-race serum electrolyte concentrations or in body weight change. In the regression analysis, the only two independent risk factors were a faster race time and a history of cramping in the previous 10 races.[2]
Medications that may play a role
In rest cramps, medication history may be relevant. A population-level analysis from British Columbia, in adults aged 50 or older, found that new cramp treatment (measured as new quinine prescriptions) was more likely in the year after starting inhaled long-acting beta-2 agonists (adjusted sequence ratio 2.42), potassium-sparing diuretics (2.12) and thiazide-like diuretics (1.48), whereas the associations for statins (1.16) and loop diuretics (1.20, not statistically significant) were small.[6] This design shows an association in prescribing patterns, not proof that a given drug causes a given patient’s cramps.
Season
Rest cramps also appear to be seasonal. Using new quinine prescriptions and internet searches as markers, the same research group found that both markers peaked in mid-summer and were lowest in mid-winter, roughly doubling from winter low to summer high. These are indirect markers rather than direct counts of cramps.[7]
Charley Horses in Athletes: Who Is at Risk?
For athletes, previous cramping stands out as a warning sign. In the Ironman cohort, a history of cramping in the previous 10 races was one of only two independent risk factors.[2]
Intensity also matters. In the Ironman cohort, athletes who cramped had faster predicted and actual race times despite similar preparation and performance histories, which the authors interpreted as racing at a higher intensity.[2]
Do Magnesium, Electrolytes or Quinine Prevent a Charley Horse?
Magnesium
Magnesium supplements are marketed for preventing cramps, but the evidence is unfavourable for older adults with typical idiopathic muscle cramps. A 2020 Cochrane review of 11 trials (735 participants) concluded that magnesium is unlikely to provide clinically meaningful cramp prophylaxis to older adults with skeletal muscle cramps.[3] For the primary outcome, the percentage change in weekly cramps at four weeks, the difference between magnesium and placebo was −9.59% (95% CI −23.14% to 3.97%; 3 studies, 177 participants).[3] The same review found no randomized trials of magnesium for exercise-associated cramps.[3]
The idea that cramps are caused by an electrolyte deficiency is a common belief. When patients ask, I usually explain that, in my view, cramps are often not simply a matter of electrolyte shortage, that altered neuromuscular control is one important proposed mechanism, and that taking magnesium is unlikely to correct typical rest cramps. This is in line with the Cochrane findings above for older adults, although the underlying causes of cramps are still not fully understood.
Pregnancy
Leg cramps are a common problem in pregnancy, but a 2020 Cochrane review concluded that it is unclear whether any of the oral interventions studied (including magnesium, calcium and vitamins) provide an effective treatment.[8]
Compression stockings
A 2026 Finnish randomized trial tested a different approach in 121 adults aged 50 to 85 who had at least two leg cramps a week. Participants used knee-high medical compression stockings, magnesium or placebo pills daily for four weeks. At week 8, the adjusted difference in the change in weekly cramp frequency between the unblinded compression stocking group and the placebo-pill group was −1.43 (95% CI −2.36 to −0.50), whereas magnesium did not differ significantly from placebo (−0.20; 95% CI −1.49 to 1.09).[9] The stocking group could not be blinded, adherence to the stockings was lower than to the pills, and cramps were self-reported, so this is a single promising trial rather than definitive evidence.[9]
Quinine
Quinine illustrates a benefit–risk trade-off. A Cochrane review of 23 trials (1,586 participants) found that, compared with placebo, quinine reduced cramp number over two weeks by 28%, cramp intensity by 10% and cramp days by 20%, without significantly affecting cramp duration. The authors rated the evidence as low quality for cramp number and cramp days and moderate quality for intensity.[4] Minor adverse events, mainly gastrointestinal, were more common with quinine; in the included trials, serious adverse events were not significantly more common than with placebo. However, because serious adverse events can rarely be fatal, quinine prescription is severely restricted in some countries.[4]
Pickle juice and “neural” remedies
Pickle juice is one of several folk remedies for cramps.[5] In a laboratory study of 10 mildly dehydrated men, drinking pickle juice shortened electrically induced cramps by 49.1 seconds compared with water (84.6 vs 133.7 seconds), with little change in plasma composition five minutes after drinking.[10] The authors suspected a reflex starting in the mouth and throat rather than electrolyte replacement. However, these were cramps of a small foot muscle induced by electrical stimulation, and the Sports Medicine review cautions that this cannot be taken as evidence of efficacy against exercise-associated cramps.[5]
What the Evidence Says About Stretching
During a cramp
Passive stretching of the cramping muscle has been described as the treatment for acute cramps, but the Sports Medicine review notes that the data originally presented for this came from a single runner whose muscle electrical activity fell sharply during stretching.[5] The authors of the French primary care study, citing earlier work, noted that stretching or contracting the opposing muscle usually speeds relief.[1]
How best to stop a cramp once it has started is less clear. Patients and acquaintances describe different approaches: some stand on the cramping leg, some massage the muscle, and others simply let it pass. In my view, current knowledge does not point to a single right answer.
Before bed, for night cramps
For rest cramps, one randomized trial in 80 adults over 55 tested nightly calf and hamstring stretching immediately before sleep for six weeks. Compared with no specific stretching, cramp frequency fell by 1.2 cramps per night more (95% CI 0.6 to 1.8), and severity fell by 1.3 cm more on a 10-cm visual analogue scale.[11] This is a single trial without a sham-stretch control, so the result is encouraging rather than definitive.
Before exercise, for exercise-associated cramps
For exercise-associated cramps, direct evidence is limited. The Sports Medicine review concluded that preventive and treatment strategies are not uniformly effective.[5]
Stretching and staying active in practice
In practice, I encourage patients with typical, uncomplicated cramps to keep moving normally and to look after their muscles, for example by stretching, even though the research evidence on stretching is mixed, as described above. Some patients become wary of physical activity because of their cramps. I tell them that moving is allowed and worthwhile, and that they can live a normal life. I also do not usually suggest that patients stop or cut back on sport; in my experience, they can often stay active within the limits of pain.
When a Charley Horse May Be Something Else
“Cramp” is a word patients use for many different leg symptoms. In the French primary care study, cramp sufferers more often had venous insufficiency, peripheral arterial disease and restless legs syndrome than patients without cramps, and the authors noted that cramps are easily confused with restless legs syndrome.[1] The Sports Medicine review points out that most of the many potential causes of muscle cramps are not related to exercise but to medical conditions or their drug treatments.[5]
Restless legs and periodic limb movements
From a clinical perspective, not every evening or night-time leg symptom that patients call a cramp is one. Some describe milder, more subtle and persistent symptoms in the evening or at night, and in many of these patients the picture is, in my view, closer to restless legs syndrome. A smaller group has periodic limb movement disorder, which is again a different entity from a true muscle cramp.
Sciatica
Back patients with sciatica are another group to keep in mind. In my experience, sciatica can sometimes cause cramping, and these patients may describe cramps in the calf or in the thigh.
A calf that stays sore
A calf that stays painful after what felt like a cramp may warrant particular attention, because ongoing pain is easily taken for ordinary muscle pain. When a patient comes to my clinic with this, I examine the leg and quite often refer them for an ultrasound, and from time to time a venous thrombosis is found behind the symptoms. Because an untreated venous thrombosis is a serious condition, I do not think this possibility should be dismissed.
For differential diagnosis, I often image the calf with ultrasound once in my own practice, particularly when the calf stays sore after cramps. Some patients describe a calf that has become “crampy”: not constantly painful, but cramping more often than usual. In my practice, this is another situation where I prefer a calf ultrasound. This describes my own approach rather than a general recommendation; whether imaging is needed depends on the clinical assessment. More generally, I palpate the calf for tenderness and usually do a basic neurological examination once to look for other findings. In my experience, checking electrolytes may not add much in explaining typical cramps themselves, although I may look at them as part of a basic assessment.
Muscle tears and Achilles tendon rupture
Sometimes a “cramp” turns out to be a muscle tear. In my experience this is not unusual, and there is often an identifiable moment behind it, such as a push-off, or a blow to a muscle that is already tensed. An Achilles tendon rupture can also feel like a cramp at first, although patients usually notice fairly quickly that the foot does not work properly or the leg feels odd. The rupture itself is not necessarily very painful, and it can come as a surprise to the patient that the tendon is torn at all, even when the clinician can clearly feel a gap in it. Patients are sometimes puzzled that they can still point the foot and toes downward; this is mainly possible because other tendons around the ankle, such as the peroneal tendons, and the toe flexors keep working. Fortunately, in my experience these injuries are relatively uncommon.
Cramps, muscle twitches and ALS
I usually tell patients that a cramp is not dangerous in itself and is generally not a sign of a more serious disease. It is true that cramps can be an early feature of amyotrophic lateral sclerosis (ALS), but ALS is so rare that cramps alone are not, in my view, a reason to suspect it; new symptoms, such as weakness or muscle wasting, would change that assessment. The same applies to muscle twitches (fasciculations). From time to time, patients come in worried that twitching points to a neurological disease. Fasciculations can occur in ALS as well, but in my view isolated twitching does not, on its own, warrant a broader work-up unless new symptoms or abnormal findings appear.
Practical Takeaways
- Night cramps are common in older adults and are often long-lasting, but in most people they are not frequent.[1]
- Nightly calf and hamstring stretching reduced rest cramps in one randomized trial, which is encouraging but not definitive.[11]
- Magnesium is unlikely to help older adults with typical rest cramps, and the 2020 Cochrane review identified no randomized trials evaluating magnesium for exercise-associated cramps.[3]
- Certain inhalers and diuretics have been linked in prescribing data to new treatment for rest cramps.[6]
- For athletes, previous cramping and faster racing were risk factors in a prospective Ironman cohort, whereas serum electrolyte changes did not differ significantly.[2]
- Compression stockings reduced cramp frequency compared with placebo pills in one 2026 trial in adults aged 50 to 85, but this is a single trial.[9]
- Quinine involves a real trade-off between modest benefit and rare serious harm.[4]
Conclusion: The Charley Horse Has More Than One Cause
The charley horse is common, painful and still only partly understood. In one French primary care study, nearly half of patients aged 60 and over reported cramps,[1] and exercise-associated cramps are a relatively common occurrence in a range of sport and exercise activities.[5] The research does not support a single explanation or a single fix. In the prospective Ironman cohort, serum electrolyte and body-weight changes did not differ significantly between athletes who cramped and those who did not, magnesium is unlikely to prevent rest cramps in older adults, and quinine trades modest benefit for rare serious risk.
What emerges instead is a more individual picture: the type of cramp, the person’s medications and medical history, and, in athletes, pacing and previous cramp history. Understanding which kind of charley horse you are dealing with is the most useful starting point.
In my clinical experience, most cramps are not dangerous in themselves, and I usually encourage patients to keep moving and live normally rather than relying on magnesium. What I pay more attention to is a calf that stays sore, a “cramp” with a clear trigger such as a push-off, or a foot that does not work properly afterwards, because these may point to something else, such as a venous thrombosis, a muscle tear or an Achilles tendon rupture.
References
- https://doi.org/10.1186/s12875-016-0509-9
- https://bjsm.bmj.com/content/45/8/650
- https://doi.org/10.1002/14651858.CD009402.pub3
- https://doi.org/10.1002/14651858.CD005044.pub3
- https://doi.org/10.1007/s40279-019-01162-1
- https://pubmed.ncbi.nlm.nih.gov/22157068/
- https://doi.org/10.1503/cmaj.140497
- https://doi.org/10.1002/14651858.CD010655.pub3
- https://doi.org/10.1186/s13063-025-09370-z
- https://doi.org/10.1249/MSS.0b013e3181c0647e
- https://doi.org/10.1016/S1836-9553(12)70068-1
