marathon training, triathlon training -
Cramps and Stitch: Why Do We Get Them and How Can We Prevent Them?
P. Mauro, 2005
Most triathletes, at one time or another would have experienced either a cramp or a stitch during a triathlon or a training session. These complaints can range from mildly uncomfortable to severely debilitating, but there is no question that they are a great source of frustration to everyone from recreational exercisers to serious athletes.  Unfortunately, scientists know very little about the two conditions and how to avoid them.  Consequently, there is a lot of folklore surrounding the topic, making it difficult to know exactly how to deal with these problems.
What is Cramp?
Cramp is a sudden, tight and intense pain that most commonly occurs in the leg muscles: especially the gastrocnemius, hamstrings, and quadriceps. It can range from a slight twinge to an excruciating pain, and may last for a few seconds or several minutes.  A cramp can be a one-off occurrence or repeat several times before the muscle relaxes and the pain goes away.
What Causes Cramp?
Cramp is caused when a muscle involuntary and forcibly contracts and does not relax. While this seems to be due to an abnormal stimulation of the muscle, the exact mechanism is unknown.  Cramp is more likely to occur in tired muscles therefore poor fitness or exercising at high workloads can increase the likelihood.  Inadequate stretching and poor biomechanics may also contribute.
Dehydration may contribute to cramp especially when fluid and sodium losses are high.  Sodium is involved in initiating nerve signals that make muscles contract.  A deficit of sodium and fluid may "irritate" muscles causing them to contract uncontrollably.
Cramp has been attributed to the depletion of potassium and minerals such as calcium and magnesium.  However, this idea does not have strong support as very little potassium, calcium and magnesium is lost during exercise.  Also deficiency is rare as these substances are abundant in the diet.  It has been suggested that magnesium is relocated in the body during exercise rather than lost in sweat.  Therefore, a magnesium imbalance in relation to other electrolytes (sodium and potassium) may be involved.  Further evidence needs to be gained in this area.
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