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Muscle Cramps and Exercise


Quite often runners and exercisers experience painful muscle cramping either during or immediately following a strenuous exercise bout and as a result, these types of cramps have become known as Exercise Associated Muscle Cramps or EAMCs. Much confusion surrounds the causes of EAMCs including dehydration to electrolyte imbalances. This article aims to explain the latest model for describing EAMCs, how to prevent them and how to deal with them once they occur.

What is a muscle cramp?

A muscle cramp is defined as a painful, involuntary, spasmodic contraction of a muscle. The muscle remains contracted and may last for a few seconds to several minutes. The muscles most prone to EAMCs are those that cross two joints - for example the calf muscle called the gastocnemius (crosses the ankle and knee joint) and the hamstrings (cross the knee and hip joint).

What causes an EAMC?

There are many theories surrounding the cause of muscle cramps. Some proposed causes are fluid loss and dehydration, electrolyte imbalances (sodium, potassium, magnesium), heat and congenital/inherited conditions. Recent evidence collected by Professor Martin Scwellnus at the Sports Science Institute of South Africa indicates no strong relationship between these causes and exercise cramps. After completing several studies and studying the results of other experiments using electromyography or EMG (measures muscle nerve electric activity), Schwellnus has proposed a novel model of the cause of EAMCs.

What is the new model for identifying the cause of EAMC's?

Dr. Scwellnus identifies two possible factors that may affect nerve activity - causing excessive muscle stimulation to contract and resulting in a cramp. The first suspected factor is fatigue; since motor nerve firing patterns have been demonstrated to be irregular during conditions of fatigue. The second factor is proposed as resulting from the muscle working too much on its "inner range" or "on slack". To explain this concept it must first be understood that a muscle cannot work efficiently if it is not at its optimal length - a muscle works progressively less efficiently when overly stretched or overly loose/on slack. The protein filaments (actin and myosin) that make up muscle fibers require an optimal "overlap" to be able to generate force. The position of the body's joints determine muscle length, so it follows that muscles that cross two joints like the gastroc and hamstrings might be more likely to operate in the slackened position and experience a cramp. For example, consider a free-style, swimmer who performs flutter kicks at the ankle with a slight knee bend. The flutter kick involves the ankle flexing and extending in a small range very near the plantarflexed (toes pointed) position. Couple this with a slight knee bend, and it makes the gastrocnemius muscle even more "passively insufficient".

Recall from our article Plyometrics and the Stretch Shortening Cycle we discussed the role and significance of the small cellular bodies of the muscle spindle and the Golgi Tendon Organ (GTO). The muscle spindle is a tiny cellular structure usually located in the middle portion of each muscle fiber. Very basically its role is to "switch on" a muscle and determine the amount of activation and the strength and speed of the contraction. The GTO is a small structure located in the tendon that joins the muscle to a bone. This structure senses muscle tension and performs the opposite role of "switching off " the muscle in order to protect it from generating so much force as to rip right off the bone.

Dr. Schwellnus suggests that when a muscle works within its inner range and/or when fatigued, muscle nerve activity shifts progressively toward muscle spindle activity (contraction) and less toward GTO activity (relaxation). More specifically, the nerves that control the muscle spindle (Type IA and type II nerves) becomes overly active while the nerves that controls the GTO (Type Ib nerves) become under active or inhibited. The result of this nerve activity imbalance is an uncontrolled, painful cramp.

What do I do if I experience an EAMC?

If you should experience an EAMC, the best solution is to perform a gentle, passive stretch of the affected muscle. Do not attempt to walk or run it off. Slow, passive stretching will act to restore nerve balance to the muscle by increasing the activity of the GTO, while simultaneously minimizing that of the muscle spindle. Stretching increases tension in the tendon, which is sensed by the GTO. The result is a relaxation of the contracted muscle and a breaking of the muscle cramp. For example, in the case of the swimmer mentioned earlier, to stretch the gastrocnemius he or she may perform a standard calf stretch while pushing against a wall or use a stretching strap or cord to pull the foot up toward the shin. To accentuate the stretch, it is important that the knee remain straight, since as mentioned this muscle crosses the knee joint.

How do I prevent EAMC's?

The best way to control and prevent EAMC's is to begin a regimented stretching routine. It may be beneficial to perform dynamic stretches after a brief warmup at the beginning of the exercise session or workout. Dynamic stretches involve using functional movements such as lunging, squatting and reaching and can be used to simultaneously train balance and core stability while sensitizing the muscles in preparation for exercise. In fact, dynamic stretches if performed correctly, may actually serve as a warm-up in themselves. Static stretching may be more effective at the end of the exercise session as part of the cool down, as the muscles will be warm and more pliable. The best long-term solution to control EAMC's however is to restore muscle balance throughout the body by combining stretching with a well-designed functional strength training routine -concentrating specifically on core stability.

In conclusion, muscle cramping is a complex condition and this article has hopefully provided the reader with a new perspective on the scientific relationship between exercise and muscle cramping. The fact that cramps occur most often in the situations described make this model a very plausible and practical one. It is hoped that this information will assist the casual exerciser and professional athlete alike in understanding and dealing with exercise related muscle cramps.

David Petersen is an Exercise Physiologist/Certified Strength and Conditioning Specialist and the owner and founder of B.O.S.S. Fitness Inc. based in Oldsmar, Florida. More articles and information can be found at http://www.bossfitness.com

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