Muscle Cramping

http://www.scientificamerican.com/askexpert/biology/biology64/>


Mark A W Andrews



Muscle cramping is a common problem encountered by athletes and nonathletes

alike. Defined as painful involuntary skeletal muscle contractions, cramps

may be categorized as either nonexercise related or exercise related. The

etiology of the former group may involve hormonal, electrolyte or metabolic

imbalances, or it may result from long-term medication. Diagnostic medical

testing may be required if cramps are a persistent problem. Exercise-related

muscle cramps (ERMC) are much more common. They typically affect the large

muscles of the legs during or immediately after exercise and last for seconds

to a few minutes. These are typically benign but result in intense pain and

may not seem innocuous at the time.



There is little definitive knowledge of the etiology of ERMC. Traditionally,

such cramping was believed to arise from dehydration, electrolyte imbalances

(including magnesium, potassium and sodium), accumulation of lactic acid, or

low cellular energy levels. These proposals, however, have been shown to have

minimal scientific value.



More recent developments indicate that the cause of cramps most likely

involves hyperactivity of the nerve-muscle reflex arc. In this scheme, some

of the normal inhibitory activity of the central nervous system (CNS)

reflexes is lost as a result of CNS fatigue or overuse of feedback

communication with muscles. These spinal reflexes use two receptors, known as

Golgi tendon organs and muscles spindles, found in skeletal muscles. Golgi

tendon organs may become inhibited and muscles spindles can become

hyperactive, leading to sustained activation of the muscle.



It has been suggested that prolonged sitting, poor or abnormal posture or

inefficient biomechanics (all of which may be related to poor flexibility)

predispose these reflexes to malfunctioning. Age also seems to predispose

individuals to cramping--the phenomenon may develop later in life for people

who exercise for years without prior problems. Other factors include

increased body weight and improper footwear. Eccentric muscle contraction and

other musculoskeletal injuries can contribute to the problem.



If a muscle's hyperexcitability is the basis of cramping, then stretching

should attenuate the response. In evidence, it is well recognized that, once

induced, stretching the affected muscle can ameliorate cramping. Stretches

should be held for 15 to 30 seconds or until the muscle relaxes and the cramp

does not recur when the muscle is returned to its normal relaxed position. In

addition, once cramping starts, exercise should be curtailed for at least an

hour, which allows the muscles and the CNS to recover. It is never a good

idea to "run through" these cramps. Applying heat to the area for a few

minutes while stretching may also help the muscle.



Prophylactic stretching of the major muscles of the lower limbs for at least

five to 10 minutes during warm-up and cool-down periods can help prevent

cramps. The importance of flexibility cannot be overstated, particularly for

older athletes. Other recommendations include minimizing running hills and

stairs (limiting eccentric contractions); undergoing a biomechanical

evaluation of your exercise technique; making sure shoes and other equipment

are appropriate and not excessively worn. If, after a few months, cramps do

not respond to these measures, see a qualified sports physician or physical

therapist.