When exercise cramps your style

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When exercise cramps your style

A cramp is a cramp is a cramp, right?

Wrong, says Ronald Haller, M.D., an MDA research grantee who has studied the effects of exercise in metabolic myopathies.

The cramps that can occur in metabolic disorders are fundamentally different, he says.

“The muscle is shortened, hard, usually intensely painful and cannot be lengthened for minutes to hours. The limb is literally locked-up.”

Lock-up cramps are triggered by exertion, says Haller, and should not be confused with spontaneous cramps that occur at rest or with the exercise-associated cramps that most athletes experience.

He also notes that unlike ordinary cramps, the muscle shortening that occurs in metabolic disorders is electrically silent. This lack of electrical activity leads Haller to believe that lock-up cramps may be caused by an abnormally hyperactive interaction between actin and myosin in the muscle fibers due to increased cellular calcium or increased calcium sensitivity.

Common muscle cramps will usually resolve with passive stretching, while lock-up cramps will not. The best way to resolve cramps caused by inborn errors in metabolism is to treat the underlying disorder.

EXERCISE-ASSOCIATED MUSCLE CRAMPS		CRAMPS DUE TO METABOLIC DISORDERS
Common		Rare
Intermittent with variable severity during exercise		Recurrent and severe during exercise
Myoglobinuria usually absent		Myoglobinuria common
Rhabdomyolysis usually absent		Rhabdomyolysis usually present
Electrical activity present during cramping		Often electrically silent (rigor)
Weak familial tendency		Strong familial tendency

Adapted from The Physician and Sportsmedicine

ISCHEMIC CONTRACTURE IN MULTIPLE CARNITINE ACYLTRANSFERASE DEFICIENCIES

Muscle contracture following ischemic exercise has been described in McArdle's disease and in phosphofructokinase deficiency. We report two brothers with multiple carnitine acyltransferase deficiencies who developed muscle contracture on ischemic forearm exercise.

These patients have a clinical history of cramps and myoglobinuria following brief intense exercise. Serum lactate elevation during ischemic forearm testing rose by a factor of 4 and enzymatic assay of muscle phosphorylase activity was also normal. However, during ischemic forearm exercise, intense stiffening of the patient's forearm muscles was observed. No electrical activity was observed with an EMG needle placed into several forearm muscles during this stiffening. This contracture was painful and persisted for over an hour, with the patient being unable to move his fingers during this time.

The activity of carnitine palmitoyl transferase (CPT) on the patient biopsied was markedly reduced to 15% of normal, as were the activities of carnitine acetyltransferase (13% of normal) and carnitine octanoyltransferase (44% of normal). Adenylate deaminase activity, citrate synthase activity and muscle histochemistry were normal.

Contracture on ischemic exercise has not been described in CPT deficiency, and we report these patients as an unusual form of CPT deficiency with multiple acylcarnitine deficiencies. The development of contracture in these patients will require a reassessment of ideas about the biochemical mechanism of ischemic muscle contracture.

Reference: Anderson, T.L, et al. Neurology (NY) 32(2) April 1982

Related links:
Stiffness, cramps and twitching

MDA Quest column with definitions, causes and neuromuscular diseases associated with each.

Columbia researchers discover new mechanism for muscle contraction
How calcium channels regulate muscle contraction.

Muscle cramps: Dealing with heat stress during endurance exercise
Article by Bill Misner, Ph.D.

Skeletal muscle cramps during exercise
Article by Martin Schwellnus, M.D.

No more muscle cramps
Web MD article by Liz Applegate, Ph.D.

To read more about lock-up cramps in CPT II deficiency, visit Seeing red, Running in the family and Pain Survey Results.

Cramping is a very common problem in all muscle diseases.

Simple measures that can help include:

stay hydrated (drink lots of water)

do daily, gentle, prolonged 30-second stretches for all major muscle groups

use heat and/or ice for any localized painful cramping.

--Gregory Carter, M.D.,
MDA Clinic Director in Olympia, WA

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