Exercise Associated Muscle Cramping (EAMC)

Exercise Associated Muscle Cramping (EAMC)
Sources: Clinics in Sport Medicine

Have you ever experienced a muscle cramp whilst doing your long run? Want to know why it happens? How to prevent it? Read on...

- What brings this about?
Exercise associated muscle cramping (EAMC) is defined as a painful, spasmodic, and involuntary contraction of skeletal muscle that occurs during or immediately after exercise. The most scientifically based hypothesis for Exercise Associated Muscle Cramping (EAMC) is the “muscle fatigue hypothesis” of Prof Martin Schwellnus and colleagues from the Sports Science Institute of South Africa.

-What causes premature muscle fatigue and EAMC?
According to a study by Manjra and colleagues of over 1300 marathon runners in 1996, certain risk factors for EAMC were identified that included:
• older age,
• longer history of running,
• higher body mass index,
• shorter daily stretching time,
• irregular stretching habits,
• and a positive family history of cramping.

More recently (2008) Schwellnus and colleagues outlined the most important risk factors for EAMC in athletes are a previous history of EAMC, and performing exercise at a higher relative exercise intensity or duration, when compared with normal training and participating in hot and humid environmental conditions. These factors could explain why not all runners suffer from EAMC during running.

These factors could then lead to premature muscle fatigue, which again leads to an altered neuromuscular control at the spinal level through abnormal reflex activity. Altered neuromuscular control results in a disruption of muscle coordination and control and the involved muscle end up cramping.

It is also well documented that the muscles most prone to cramping are those that span across two joints including the gastrocnemius (calve muscle), hamstrings and quadriceps muscles.

There are 4 other schools of thought for causing exercise associated muscle cramping (EAMC) including the electrolyte depletion theory, the dehydration theory, the metabolic abnormality theory and the environmental theory, but these hypotheses have little scientific support:

Electrolyte depletion theory
This theory suggests that abnormalities in electrolytes such as Sodium Chloride, Magnesium, Calcium, Potassium and Phosphate could result in skeletal muscle cramping.

Dehydration theory
The earliest reports linking dehydration and EAMC in mine workers, cane-cutters, and firemen were case series, and no direct measure of hydration status was documented.

Metabolic abnormality theory
Various inherited metabolic abnormalities are associated with skeletal muscle cramping during exercise. These include abnormalities in carbohydrate and lipid (fat) metabolism and acquired medical diseases such as diarrhoea, diabetes, thyroid disease ect. There is however little support that the most common form of EAMC is caused by these abnormalities

Environmental theory
This theory is based on the term “heat cramps” found by Talbot in 1935. More recently running in hot, humid environments have been described to result in secondary physiological changes, which can cause EAMC, but heat alone is not a direct cause of EAMC.

- What can you do to manage an acute episode of EAMC?
An episode of EAMC can almost always be anticipated if the involved muscle starts to twitch whilst running and by just running a bit slower the cramp can be avoided. However, if the cramping episode does occur without warning the most effective immediate management of EAMC is relative rest and passive stretching for 30-60 seconds or until the cramping ceases. Icing the area for 10 minutes has been found to be of benefit. Avoid massaging the muscle as it will be too painful.

- How can it be avoided?
• The key to preventing EAMC is to reduce the risk of premature muscle fatigue:
• This can be done by taking care not to over train (high intensity and/or long duration) if not used to it.
• Make sure you’re well conditioned before taking on strenuous races.
• Limit participating in hot and humid environmental conditions as this could lead to EAMC.
• Adequate nutritional intake (carbohydrate, electrolytes and fluid) to prevent premature muscle fatigue during exercise.
• If you are prone to recurrent EAMC, perform running at a lower intensity for a shorter duration and seek medical advice.
• Mineral and Electrolyte supplements such as Calcium, Magnesium, Potassium, Phosphates ect will only be of value if you have a deficiency.
• Flexibility training of the most likely muscles to cramp i.e : Hamstrings, Quads and Calves. Stretch at least 2x per day, hold the passive stretch for 30 seconds and repeat 3x.