The Latest on Charley Horse: How Muscle Cramps Work

No one knows for certain how “charley horse” became a name for muscle cramps.  Baseball lore from the late 1800s links the term to a player named Joe Quest, who may or may not have compared his cramp-prone teammates to an old, stiff-legged white horse named Charley who pulled heavy loads in his father’s machine shop in New Castle PA. The first newspaper story using the term charley horse in the context of players who pulled up with thigh cramps was allegedly the Chicago Tribune, during Quest’s 1879-1882 stint with the Chicago White Stockings. The first retrievable story using the term, in the Boston Globe in 1886, referred to the Tribune story as the origin of the name. By that time, Quest was with the Philadelphia Athletics and at the end of his career, but the off-hand description he may or may not have coined has become a household word, spread far beyond the world of baseball.

What is a muscle cramp?

Muscle cramps of are involuntary, intense and painful contractions which harden the muscle and last seconds to minutes. Aching pain and even chemical indications of muscle damage may persist much longer.  Electrical recording of muscle activity during cramping and between bouts of cramping indicates that the baseline or normal amount of electrical activation of the muscle is increased – maybe a measurable correlate of the feeling that a muscle is “about to cramp.”

Theories about cramps

Long-held theories have blamed muscle cramps on dehydration, electrolyte losses from sweating, extreme environmental conditions of heat and cold, or inherited problems of energy production. In addition, cramps happen more in people taking some medications some medications such as cholesterol lowering drugs and diuretics. While these factors may play supporting roles, they do not explain the mechanism of cramping. Nor do they explain why stretching, as well as folklore-based remedies like the Amish combination of vinegar, ginger and garlic, or consumption of pickle juice, mustard or hot peppers help cramps. Newer, “neural” theories about the mechanism of cramping, which implicate feedback loops between muscle and the spinal cord, might account not only for exercise related cramps but also for and the kind that grab hold of a leg as you roll over in bed.  And they might explain the seeming success of peculiar remedies. To understand the neuromuscular feedback loops we must diverge briefly into a little muscle anatomy and physiology.

How your muscles move things

When you decide to lift this magazine, your brain sends a message to motor nerve cells in the spinal cord, the alpha motor neurons, which then fire signals down nerves to the biceps muscle and to all the other muscles are involved in the task, telling some to contract and others to relax.   That is the simple part. The complex part, which goes on in the background at all times, is the feedback from two types of specialized muscle receptors which act much like strain gauges used in civil engineering to detect forces deforming land and buildings.

Strain gauges in every muscle: moderators of muscle tone

One type of muscle receptor strain guage is a muscle spindle. It calculates stretching forces in the belly of a muscle. The other is a Golgi tendon organ, which calculates the stretch in the tendon, the fibrous end of the muscle that attaches to bone.  Muscle spindles send messages to the spinal cord motor cells to fire up and contract the muscle when the muscle lengthens too much. Golgi organs send the opposite message to prevent the tendon from becoming too tight as the muscle contracts. All of this occurs rapidly and constantly, in a balance that keeps your muscles at the right degree of tone for all your movements.

In 1997, researchers suggested that unbalanced feedback from these little muscle strain gauges was the primary cause of cramping.  In fatigued muscle, at least in animal studies, the spindles were more active than normal, and the Golgi tendons less active.  The net result caused alpha motor neurons to fire up the muscle fibers than they usually do. Passive stretching of the muscles, which stretches tendons, woke the Golgi receptors back up, prompting them to send more cease and desist orders to the motor neurons. The cause of cramping thus appeared to be too much spindle input.

Regulation from above

Motor neuron feedback loops also receive input via pathways that originate higher in the nervous system. Swallowing liquids with striking tastes stimulates sensory cells in these spinal pathways, sending messages up to the brain and down through the spinal cord. Cramp researchers speculate that stimulation of these pathways tamps down some of the incoming messages from the muscle spindles, providing an explanation for the efficacy of some old-fashioned cramp remedies.

The well-known tendency of baseball players to suffer cramps might also bolster the neuromuscular feedback theory.  Baseball players wait to explode into motion from crouches, get up from slides to race back to safety after failed base stealing attempts, and stop, start and reverse direction abruptly.  It is easy to imagine some Golgi tendon organs and muscle spindles lulled into altering their feedback and then lagging in adjusting to the abrupt new actions.

Cramps in bed

But what about the cramps that are not associated with the fatigue of exercise? Shortening of the muscle in certain positions, such as lying in bed, may set them up for the same imbalance in input from the stretch receptors. The increasing frequency of cramp problems with age could be a result of general loss of strength and flexibility in muscles that are not used as much as in the past.  The ideal input from muscle stretch receptors occurs in the rested muscle which has maintained its youthful length and flexibility.

Practical application of the latest theory

Practical application of the neuromuscular feedback theory of cramping applies not only to charley horses, but also to musculoskeletal injury prevention in general.  Maintenance of flexibility and balance of strength in opposing muscle groups such as the quadriceps and the hamstrings keeps the spindles and Golgi tendon organs in balance, and muscles which are less stiff and prone to cramping allow movement with less discomfort as life moves on. Such maintenance requires regular work, especially if you want to avoid some of the creeping stiffness of old age.

Note: the muscle receptors and their connections  may well play roles or even be the culprits in some mysterious muscle disorders that are associated with cramping or decreased muscle tone. Muscle research is a blossoming field in this new age of genetic research. All muscles bear the stamp of their genetic makeup in their differing structural proteins. Some people have big bulky muscles, some long slender ones; some have more fast twitch fibers that make them speedy, others more slow twitch fibers that endure for marathons.  And some people are relatively inflexible, others loose and prone to twisting ankles. You get what you get from the usual complement of both parental versions of DNA, in the nucleus of the cells. (But if you want to complain about your speed, blame your mother- she provided all the DNA in the mitochondria which power the cells.)

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