What Causes Muscle Cramps?

 

Do you ever experience muscle cramps?  I know I have and they are not fun!

Here is a discussion on the causes of muscle cramps.

Muscle cramps can stop athletes in their tracks. Although they usually self-extinguish within seconds or minutes, the abrupt, harsh, involuntary muscle contractions can cause mild-to-severe agony and immobility, often accompanied by knotting of the affected muscle. And cramps are common; 50%–60% of healthy people suffer muscle cramps during exercise, sleep or pregnancy or after vigorous physical exertion. There is no gender difference with skeletal muscle cramps, but they appear to occur more often in endurance athletes and in the elderly.

During endurance exercise, muscle cramps correlate with the length and intensity of workouts. Fitness pros and clients frequently talk about muscle cramps, but until recently, little has been known about their actual physiology.

Types of Muscle Cramps

Muscle cramps can be  categorized into three groups:

  • Nocturnal cramps occur during sleep without any clear trigger.
  • Pathological cramps are a consequence of having diabetes, nerve dysfunctions or metabolic disorders.
  • Exercise-associated muscle cramps occur during or after exertion. The first scientific confirmation of these types of cramps dates to 1908, when they were described in miners working in hot and humid conditions.

Muscle Cramp Risk Factors

With marathon runners, research has found certain risks associated with the occurrence of a muscle cramp. These risks include a longer history of running,  advanced age, higher body mass index, shorter daily stretching time, irregular stretching habits and a family history of cramping.  The two most important observations from the research are that exercise-associated cramps for marathoners are muscle fatigue (linked to longer runs) and poor stretching habits.

Early Theories About Muscle Cramp Causes

Early theories on the source of muscle cramps focused on electrolytes, dehydration and the environment.

There three early theories on the causes of exercise-associated muscle cramps.

SERUM ELECTROLYTE THEORY

Blood plasma contains electrolytes, such as sodium, potassium, chloride, bicarbonate, calcium and phosphate. Although electrolyte depletion is often blamed for causing cramps, there currently is no solid explanation of how low serum electrolyte concentrations can result in the condition. There are two studies that measured serum electrolyte concentrations in endurance runners at pre-race, immediate post-race and at 60-minute post-exercise recovery. Neither study found a connection between post-race recovery, muscle cramps and changes in serum electrolyte concentrations.

DEHYDRATION THEORY

In the past, studies have suggested treating muscle cramps in workers and firefighters with fluids and electrolytes. But those studies did not measure hydration. More recent studies that have estimated blood volume and plasma volume do not support the theory that dehydration has a direct link to exercise-associated cramps.

ENVIRONMENTAL THEORY

This theory sprang from the condition referred to as “heat cramps.” While exercising in a hot, humid environment may be correlated with the development of muscle cramps, no evidence shows cramps are linked to an increase in core body temperature.

Current Theory on Muscle Cramps

The newest concept of muscle cramps is a neuromuscular theory. This theory has evolved to point to two origins: a central (spinal column) and a peripheral (neuromuscular junction).

The central or spinal origin theory suggests that the involuntary contraction of a muscle occurs when nerve messages to the spinal column are altered, perhaps due to muscle fatigue. This results in an imbalance of excitatory (from muscle spindles) and inhibitory (from Golgi tendon organs) spinal messages to muscles. This neural signaling imbalance leads to enhanced muscle cell excitability and cramping.

With the peripheral origin theory, scientists suggest there is abnormal excitation of the motor nerves terminal branches to the muscle, causing cramping.

The scientific evidence of a neuromuscular theory is mounting. The research appears to show that, in some cases, fatigued muscle can’t fully relax. This condition leads to an imbalance between excitatory signals and inhibitory messages to the muscle. So the most recent research appears to support the central origin theory of the muscle cramp.

For more information on the causes of muscle cramps, contact Maurie Cofman, CMES, CES, TBMM-CES, Personal Trainer, Certified Medical Exercise Specialist, Health Coach and Corrective Exercise Specialist in the St. Louis, Brentwood, and Clayton, MO area.