I always get cramping in my calves when I run over 15 miles. Cramping can certainly be a symptom of "hitting the wall." I decided to search the web for some information; my findings below.
Possible Muscle Cramp Causes
• Electrolyte depletion (sodium, potassium, magnesium & calcium)
• Low blood sugar
• Poor conditioning
• Muscle fatigue
• Doing a new activity
• Exercising in extreme heat
Possible Ways to Relieve Muscle Cramps
• Stretch the muscle until the cramp stops
• Apply deep pressure to the affected muscle for 10-15 seconds at a time
Possible Ways to Prevent Muscle Cramps
• Stretch regularly after exercise
• Warm up before exercise
• Improve fitness
• Start a sports massage regime
• Make sure you are getting adequate amounts of Sodium, Potassium, Magnesium, Phosphorus & Calcium in your diet; consider taking a supplement
• Consume an electrolyte drink during extended periods of exercise
• It takes 2 to 2.5 hours of exercise to deplete fully stored muscles takes.
• Sports drinks should be diluted to a ratio of two parts to one part water to prevent high concentrations of ingredients in the system. Large meals and fatty or high protein foods should be avoided before an event or training, favoring instead smaller, more frequent snacks.
• It's widely believed that potassium, magnesium and calcium can assist in the prevention of running cramps. Supplements can be taken.
• Luke Hoffman, author of the HowStuffWorks article How Aspirin Works, offers the following thoughts on muscle cramping:
"There is a reflex arc – made up of the muscle, the nerves carrying signals to the central nervous system (CNS) and the nerves carrying signals from the CNS back to the muscle -- that keeps carrying contraction signals from and to the muscle. This appears to lead to a sustained contraction in the muscle, also known as a cramp."
• Poor posture or inefficient biomechanics can be a cause of muscle cramping. Poor movement patterns may cause a disturbance in the activity of the Golgi tendon organs. These are "strain gauges" built into the tendon to prevent muscle tears. When activated, these organs cause the threatened muscle to relax while stimulating the antagonistic muscle-the one that moves the joint in the opposite way-to fire. There may be some quirk of body mechanics that upsets a Golgi device and sets off the cramping pattern.
If this is the cause, prevention may involve improving biomechanics, and regular stretching and strengthening of muscles that seem to cramp along with their antagonistic muscles.
• Another theory is that cramping is a result of burning protein for fuel in the absence of readily available carbohydrate. In this research, muscle cramps occurred in subjects who reached the highest levels of ammonia release during exercise. High ammonia levels indicate that protein is being used to fuel the muscles during exercise. This may indicate a need for greater carbohydrate stores before, and replacement of those stores during intense and long-lasting exercise.
• Some say pinching your upper lip can release a cramp. Who knows!