Causes of Hamstring Cramps

You're just getting into the groove on a run or you're snug under the covers drifting off to sleep, when suddenly a sharp pain shoots through your hamstrings. It's a surefire way to end a perfectly good exercise session or a restful night's sleep.

Whether this is the first time you've had a hamstring cramp or you experience them often, you're likely eager to find the cause and the solution. Unfortunately, it's not so straightforward because there are numerous possible causes of muscle cramps.

Muscle cramps, also called "charley horses," are sudden, involuntary contractions of one or more muscles. Along with pain, the muscles become hard and tight, and you might feel spasms and see the muscle visibly twitching. Symptoms last from a few seconds to several minutes before disappearing, but the muscle may remain sore afterward.

Muscle cramps can happen anywhere in the body, but they are most likely to affect the leg muscles. When the cramp occurs in the hamstrings, it can affect any one, or more than one, of the three muscles that comprise this muscle group: the biceps femoris, semitendinosus and semimembranosus.

Leg cramps often occur during exercise activity, but they can also happen at night or when you are at rest for seemingly no reason. Although anyone of any age can get a hamstring cramp, certain factors increase the risk:

• ​Age:​ Older people have less muscle mass. What they do have can become overtaxed more easily.
  
• ​Pregnancy:​ The exact cause is unknown, but it likely has to do with the increased weight pregnant people carry around and changes in blood circulation.
  
• ​Being overweight​
  
• ​Engaging in endurance sports​
  

Most hamstring cramps are harmless. The most common benign causes during activity include:

• Not stretching before exercise
  
• Strenuous activity in hot weather
  
• Dehydration
  
• Muscle fatigue
• Overexertion

Common causes of nocturnal hamstring cramps include:

• Sitting for long periods of time
  
• Spending a lot of time standing on hard surfaces such as concrete
  
• Previous vigorous activity
• Sitting improperly

Sometimes underlying medical conditions can be the cause of muscle cramps. If your cramps are not related to any of the benign causes, it's a good idea to see your doctor. You may already know you are at risk, or you may be unaware that certain conditions could be causing your cramps including:

• Circulatory problems caused by narrowing of the arteries
  
• Magnesium or potassium deficiency
  
• Spinal cord injury
  
• Pinched nerve
  
• Diabetes
• Neurologic disorders
• Metabolic disorders
• Structural issues with the legs

Certain medications can also cause leg muscle cramp such as:

• Diuretics, including furosemide
  
• Asthma medications, including albuterol and terbutaline
  
• Statins
  
• Neostigmine
  
• Nifedipine
  
• Raloxifene
  
• Tolcapone
  

This is not a complete list. If you take medications, it's possible that one of them could be causing your hamstring cramps. The best way to find out is to ask your doctor.

​Read more:​ What Are the Causes of Leg & Foot Cramps?

If your muscle cramps are related to a medical condition, treating the underlying condition will help alleviate symptoms. If they are the side effect of a medication, you and your doctor will need to weigh the pros and cons of the medication's effectiveness versus its side effects.

​Treat Nutritional Deficiencies.​ Your doctor should treat nutritional deficiencies. If you are low in magnesium or potassium, your doctor will recommend increasing your intake through food or a supplement.

Magnesium is commonly recommended as a treatment for leg cramps; however, in the absence of a deficiency, it is likely unhelpful in the general population. In a 2017 study in JAMA Internal Medicine, participants with recurring nocturnal leg cramps were given a magnesium oxide supplement or a placebo once daily at bedtime. At the end of four weeks, the magnesium was found to have no better effect at reducing muscle cramps than the placebo.

​Magnesium for Pregnancy.​ But pregnant people may benefit from a magnesium supplement. A 2015 study in Maternal & Child Nutrition gave healthy pregnant adults with leg cramps either magnesium bisglycinate chelate or a placebo. Researchers found that magnesium supplementation significantly reduced leg cramp frequency and intensity compared to the placebo.

​Medications for Muscle Cramps.​ If prevention tactics don't work for reducing the frequency and intensity of your muscle cramps, there are some supplements and medications that might. According to Cleveland Clinic, the following may help relieve cramps:

• Vitamin E
  
• Vitamin B complex
  
• Diphenhydramine
  
• Calcium channel blockers

To prevent hamstring cramps before activity — especially long-duration activities — make sure to stretch. Stretching before bed may also help prevent nocturnal leg cramps.

Staying hydrated is crucial. Fluids aid proper muscle contraction and relaxation and keep the muscle cells hydrated. Drink water throughout the day and before, during and after exertion. Drink more water if you are very active and/or exercising or working in a hot climate.

For nocturnal muscle cramps, riding a stationary bike briefly before bed may help prevent muscle cramps.

When the pain strikes, you can find hamstring muscle cramp relief by stretching. Sit on the floor with your legs extended. Walk your hands down your shins until you feel a stretch in the backs of your legs. Hold for 30 seconds.

If you're in bed when a cramp hits, you can extend the affected leg, wrap the bed clothes around the bottom of the foot and gently pull the leg toward you.

After you've stretched the muscle, apply a heating pad to further relax your hamstrings. You can also gently massage the muscles with your fingers.

Although hamstring muscle cramps aren't typically anything to worry about, if you get them frequently for no apparent reason, give your doctor a call. You should also call your doctor if your hamstring cramps are accompanied by swelling, tenderness, redness or warmth in the affected area or if the pain doesn't go away or if you have trouble walking.

​Read more:​ Vitamins & Minerals for Leg Cramps