What causes them and what to do about them?
By Bernie Clark, May 1, 2022
Figure 1: Getting a cramp during yoga is not uncommon. Photo by Shutterstock.
Shavasana is coming, but not quite yet. After 90 minutes of a delightful, sweaty practice, you just have a couple of more pose to do, starting with headstand. You position your head between your hands, walk you feet towards you, heels lift while your toes press into the floor ready to lift up with straight legs. With the feet plantarflexed your legs are about to rise…but, instead you collapse to the floor, grab your calf, cry, “Ow, ow, owowowow…”, while vigorously massaging your rock hard muscle. Your teacher walks over and in his Australian accent says, “ouch, a corky!” The student beside you from England calls it a “chopper”. “Charlie Horse!” suggests someone from across the room.[i] Whatever it is called, all you know is that your calf muscle has cramped and it is damn painful.
What is a cramp?
Would you like a technical description of what just happened? “A muscle cramp is a hyperexcitable neurologic phenomena of excessive, involuntary muscle contractions.”[ii] (You did ask.) At a simpler level, a cramp is a muscle that is strongly engaged and won’t release. The contraction is strong, long, involuntary and often very painful. Even once the cramp has ended, the after-pain may linger for a day or more. Why did your muscle do that? If you want a deep dive into details, read on, but if you prefer your anatomy lessons more on the lighter, summary side, feel free to skip ahead to the section on what causes cramps.
How muscles work
Our muscles can be thought of as tubes within tubes, as shown in figure 2. The smaller tubes can be called a muscle fiber or a muscle cell. Unlike most cells, muscle cells contain many nuclei and thousands of little power plants called mitochondria, which produce a chemical battery called ATP (adenosine triphosphate). Even within the muscle fiber, there are smaller tubes, called myofibrils, and within them are contracting segments called sarcomeres consisting of overlapping strips of actin and myosin proteins, as shown in figure 3. It is inside the sarcomeres where all the action happens.
Figure 2: Muscles can be described as tubes within tubes. Illustration by Shutterstock.
Notice, as shown in figures 3 and 4, that the myosin proteins have bulbous heads that attach to binding sites on the actin molecule and then the heads flex, pulling the actin towards the midline of the sarcomere, depicted as the M-line. This flexion of the myosin head is the power stroke of muscle contraction, but in order for this to occur, several other things precede it.
Figure 3: The sarcomeres are the contracting units within the myofibrils. Illustration by Shutterstock.
A signal from a nerve causes calcium ions inside the muscle cell to be released. These ions bind with proteins called troponin (the little red balls in figure 4), which are lying overtop the actin molecule, to change shape. When the troponin changes, it allows a long, filamentous protein called tropomyosin (the long yellow lines) to move, uncovering myosin-binding sites on the actin molecule (shown in blue). With these binding sites uncovered, the heads of the myosin can now “grab” onto the actin through an electrostatic attraction. This is the binding stage.
Notice that beside the myosin head shown in figure 4 are two molecules, labeled ADP and Pi. This is adenosine diphosphate and a phosphate ion. When the power stroke occurs and the myosin head flexes in a sharp, snapping movement, these two molecules are released. The muscle has just contracted. But, the story is not over and this is where things are rather interesting.
Figure 4: Muscle contraction occurs when the heads of the myosin molecules flex, pulling the actin filaments closer to the center of the sarcomere. Illustration from Shutterstock.
In order for the muscle to relax and get ready for another contraction, the heads of the myosin have to let go of the binding spot on the actin molecule and the calcium ions have to be removed from the area. As shown in figure 4—stage 3, an ATP molecule is required to unlink the myosin. Once it is unhooked from the binding site, the ATP molecule hydrolyses into ADP and Pi, which causes the head to extend (it becomes “cocked”), ready for the next cycle. All of this requires energy.
In other words, it takes energy to relax! It is important to realize this fact in order to understand why cramps may occur.
What causes cramps?
With the above little lesson in muscle activations behind us, we can now start to look at what causes a cramp.[iii] Unfortunately, the answer is not simple. There are many possible causes, and thus many possible cures. Table 1 shows one list of possible pathologies or causes of cramps.[i] But, in general, we can summarize the cause of a cramp into two main categories: those caused by some nerve dysfunction (neurogenic) and those caused by some muscular dysfunction (myogenic).
Table 1: Common causes of cramps | |
Physiologic | Dehydration Exercise Nighttime leg cramps Pregnancy Unknown (idiopathic) |
Metabolic | Malnutrition Cirrhosis of the liver Hypothyroidism Uremia |
Medication | Statins Beta-agonists Diuretics |
Neuromuscular disorders | Isaac’s syndrome Amyotrophic lateral sclerosis (ALS) Charcot-Marie-Tooth disease Acquired neuropathy Radiculopathy Metabolic myopathies |
Other neurologies | Stroke Multiple Sclerosis (MS) Parkinson’s disease Dystonia |
If a cramp has a neurogenic cause, this indicates that the nerves may be over-activating the muscle cells, or under-activating the relaxation cycle. This may be caused by over stimulation of the nerves or any of the neuromuscular disorders listed in table 1. Myogenic causes may include a lack of muscle fitness, muscle exhaustion, dehydration along with a lack of electrolytes, or possibly a lack of glucose to the muscle.
It is not unusual for cramps to occur in athletes towards the end of game, run or activity, when the body is tired, dehydrated and empty of fuel. Without enough electrolytes, the nerves cannot perform their job properly. A shortage of sodium, potassium or calcium can stop the nerves working properly. Without enough glucose, the muscles cannot create enough ATP via the mitochondria. Without ATP, the myosin heads remain attached to the actin binding sites! Again, it takes energy to relax the muscle (which is why dead bodies often enter a state called rigor mortis.[iv])
What to do about a cramp during a yoga class?
Cramps in a yoga class usually occur later in the class, when the body is tired, hot and possibly dehydrated. However, simply drinking water alone may not help resolve a cramp, because pure water may further dilute the density of electrolytes in the body. Instead, combining water with electrolytes and glucose is a much better treatment for preventing or resolving a cramp. This is one reason why so many athletes choose to consume sports drinks: the fluids have a good balance of electrolytes and glucose along with water. (Pickle juice is one currently recommended fluid: just one sip seems to release muscle cramps for many, but not all, people.[v])
Of course, intuitively, anyone with a cramp begins to massage the muscle. This helps to move blood and thus electrolytes and glucose into the muscle. Since the muscle is strongly contracted, stretching the muscle is also recommended. While this can be painful, it may help to release the contracted state. If you are suffering a calf muscle cramp, strong dorsiflexion of the foot may release it. Standing and walking around may be enough of a stretch, or try Down Dog, pulling the heels to the floor, or a low lunge with the knee gliding in front of the toes. In sports, it is often a trainer who is forcefully dorsiflexing the athlete’s foot to help stretch out the contraction. Maybe a helpful teacher can do this for you if you cramp up during a yoga class.
As shown in table 1, there are many potential causes of cramping. If you suffer frequent cramps and they are not always at the end of a hot yoga practice, you may want to have your health care provider investigate the situation more carefully, if only to rule out any serious neurological dysfunction. This is also good advice for anyone suffering premenstrual cramps or cramps during pregnancy.[vi] And, sometimes, we just don’t know why we get cramps. These are termed idiopathic cramps, which means we are just idiots trying to figure it all out.[vii]
Cramps can be painful and intense but they are rare for most people. If you get an occasional cramp, say once a year, it may be sufficient to massage it, re-hydrate, preferably with some electrolytes, and walk it off. However, if you know that you have one of the conditions listed in table 1, or if you are frequently getting cramps, it is a good idea to discuss this with your health care provider. If your cramp occurs towards the end of your yoga practice, you may be tired or depleted: your body may be asking you to stop now and have an extra long shavasana. What a lovely suggestion!
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[i] Katzberg HD. Neurogenic muscle cramps. J Neurol. 2015 Aug;262(8):1814-21. doi: 10.1007/s00415-015-7659-x. Epub 2015 Feb 12. Erratum in: J Neurol. 2016 Jan;263(1):197-8. PMID: 25673127.
[ii] Katzberg HD and Sadeghian H. Muscle Cramps. July/August 2019 Practical Neurology. https://practicalneurology.com/articles/2019-aug-july/muscle-cramps/pdf.
[iii] Here is a link to a video that helps to visualize how muscles contract.
[iv] When muscle cells die, calcium ions are released from their storage depots, which cause the myosin binding sites on the actin molecules to be uncovered. The myosin binds with the actin and contracts the muscles. But, since the cell is dead, there is no source of ATP production, thus there is no ATP available to relax the muscles. They remain permanently contracted. See the article What Causes Rigor Mortis by Anne Marie Helmenstine.
[v] Tapper EB, Salim N, Baki J, Zhao Z, Sundaram V, Patwardhan V, Nikirk SJ. Pickle Juice Intervention for Cirrhotic Cramps Reduction: The PICCLES Randomized Controlled Trial. Am J Gastroenterol. 2022 Apr 13. doi: 10.14309/ajg.0000000000001781. Epub ahead of print. PMID: 35416793.
[vi] The uterus is a muscle and like all muscles, it can sometimes cramp. The release of hormone-like compounds around the time of menstruation, such as prostaglandins, can trigger menstrual cramps (called dysmenorrhea). The uterus contracts during menstruation in order to slough off its lining. That is normal, but if these hormone-like compounds start to affect other muscle tissues in the pelvic or abdominal areas, unwelcomed cramps can occur there as well.
[vii] The term idiopathic is related to idiocy or idiot. It is formed of the Greek terms idios and pathy. Idios means “one’s own” (like “idiom”) which can be taken to mean a layperson, someone who is ignorant or someone lacking professional skills. Pathy means “to suffer”, as in the word sympathy which means that we share the suffering of others.