Muscle cramps occur most often at night when you are sleeping, but they also can occur when you exercise vigorously, tear a muscle, or keep one leg in an awkward position, such as sitting in a chair in the same position for a long time. Muscle cramps are classified into those that occur during exercise and those that can occur at any time not related to exercise, usually at night.
Cramps That Occur During Exercise
Lack of electrolytes is a more common cause of muscle cramps during exercise than lack of water (BMJ Open Sport Exerc Med, Mar 5, 2019;5(1):e000478). Electrolytes are minerals that are essential for body functions, including sodium, potassium, calcium, bicarbonate, magnesium, chloride, and phosphate. Having low blood levels of sodium (salt) is a well-known cause of muscle cramps (Clin J Am Soc Nephrol. 2007;2:151–161). Dehydration, by itself, is a far less common cause of cramps (Br J Sports Med, 2013 Jul;47(11):710-4). You can be salt deficient and still have normal blood levels of electrolytes.
Researchers in Australia studied runners who drank either plain water or an electrolyte solution before and after exercise. They found that the runners were at increased risk for suffering muscle cramps when they drank plain water, probably because water dilutes the electrolyte concentration in the body and doesn’t replace what they lost through sweating (J Int Soc Sports Nutr, Mar 15, 2021;18(1):22). In this study, 10 men ran multiple sessions on a downhill treadmill in a hot (95 degree F) room for 40 to 60 minutes, to sweat enough to lose 1.5-2 percent of their body weight (about two pounds). They were then tested before, immediately after and 40 minutes after exercising, with two trials: first, drinking plain water; and second, drinking an electrolyte solution. The tests used a special device that electrically stimulated their calf muscles enough to cause muscle cramps. The runners developed muscle cramps on much lower electrical stimulation frequencies after drinking plain water than after drinking the electrolyte solution. These results suggest that lack of electrolytes is more likely to cause muscle cramps than just lack of water (dehydration).
Cramps are more likely to occur in hot weather because muscles fatigue earlier with higher temperatures. Cramps are more likely to occur during intense exercise that requires you to use your fast twitch strength fibers that fatigue earlier than your slow twitch endurance fibers.
Night-Time Leg Cramps
Up to 60 percent of North American adults suffer from occasional night-time leg cramps, a sudden painful contraction usually of the calf muscles that can last from a few seconds up to 10 or more minutes. Doctors do not know what causes these cramps, but most of the time, they are not caused by dehydration or lack of minerals. The leading theory is that most night-time leg cramps are caused by lack of a normal nerve reflex that causes a muscle fiber to relax when it is held in contraction (J Sports Sci, 1997 Jun;15(3):277-85). That is why people who suffer recurrent leg cramps should be checked for:
• all conditions that can cause nerve damage, including lack of vitamin B12 and diabetes
• all conditions that can cause blood vessel damage such as arteriosclerosis
• partially obstructed blood vessels
• pinched nerves in the back
• muscle damage
• abnormal mineral levels
• abnormal hormone levels such as low thyroid
• kidney disease
• use of several medications such as statins, birth control pills, diuretics, steroids, asthma medication such as albuterol, raloxifene, naproxen, or teriparatide (BMJ Clin Evid, 2015:1113).
If you have recurrent night-time leg cramps, check with your doctor.
What Causes Leg Cramps?
When you turn during sleep, you contract your calf muscles which stretches their tendons. This stimulates nerve stretch receptors in the tendon and sends a message back to the spinal cord, telling the calf muscles to contract. After you contract a muscle, reflex messages are sent along nerves to the spinal cord to relax that muscle. If the message to relax that muscle is blocked, the muscle stays contracted and you develop a cramp. Cramping during sleep is usually due to an exaggeration of the normal muscle reflex that causes the muscle to stay contracted and hurt. Older people and those who do not exercise are at increased risk for leg cramps because they have smaller and weaker muscles.
Preventing Night-Time Leg Cramps
If you do not have a serious cause, you can often prevent night cramps by:
• exhausting the stretch reflex before you go to bed by stretching your calf muscles (using wall pushups or a similar exercise)
• applying a heating pad for 10 minutes before you go to sleep
• starting a regular supervised exercise program to strengthen your calf muscles. If you are a non-exerciser, I recommend a stationary bicycle.
The only drug that has been shown to be effective in preventing night-time leg cramps is quinine (Brit Med J, Jan 7, 1995;310(6971):13-17), but the U.S. Food and Drug Administration stopped over-the-counter marketing of this remedy because of concerns about irregular heartbeats. Doctors can still prescribe quinine pills for relief of leg cramps, but since they can cause birth defects and miscarriages, they should never be taken by a pregnant woman. Quinine can also cause ringing in the ears, headache, nausea, disturbed vision, chest pain, asthma and other problems. Some people may benefit from calcium channel blockers, such as amlodipine, or Carisoprodol (a muscle relaxer that blocks pain).
Treating a Leg Cramp
When you get a leg cramp, stop whatever you are doing and try to gently walk it out while you massage the contracted muscle with your hands. Never put force on the contracted muscle because you may tear it. If the cramp continues, apply cool compresses, which can relax the contracted muscle and numb pain. Keep on gently massaging the muscle.
Most leg cramps are harmless, but frequent muscle cramps can be a sign of serious medical conditions. If you suffer leg cramps only during exercise, eat salty foods or drink electrolyte solutions, not plain water, before and after you exercise. If that doesn’t stop the cramps, you need a complete medical work up. People who suffer frequent night-time leg cramps that do not respond to the simple steps listed above also need a detailed medical work up. Check with your doctor.