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Posted: November 3, 2005

Sports Medicine: New Theories on the cause of Muscle Cramps and Side Stitches

Fighting Muscle Cramps

Researchers from the University of Cape Town, South Africa, are leading the assault into understanding the erratic, painful and involuntary muscle contractions they refer to as exercise associated muscle cramps. Research has shown that up to 67% of endurance athletes experience muscle cramps at some time.(1)

Muscle cramps have been attributed to electrolyte abnormalities (particularly sodium and potassium), metabolic abnormalities, dehydration and even environmental factors such as exposure to heat and cold. In a recent analysis of each of these theories, however, the evidence against each was questioned.2 For example, it has been demonstrated that muscle cramps are not related to abnormal concentrations of sodium, potassium, magnesium, calcium or any electrolyte in the blood.(3) Furthermore, heat or cold exposure are more likely to be secondary, not primary, causes of cramps.

This has led researchers to develop a new theory to explain cramps. An understanding of this new theory, however, requires a crash course in basic muscle physiology. Within the muscle there are two structures that assist in muscle control. When activated, the first structure — called the muscle spindle — causes the muscle to contract when being overstretched to avoid damage.

The second structure — the golgi tendon organ — when activated, causes the muscle to relax when being put under too much tension.

When the muscle is fatigued it seems the activity of the structure which contracts the muscle increases, causing the muscle to contract more forcefully, while the activity of the structure which causes the muscle to relax decreases, allowing the more forceful contraction to occur. The net effect is that the muscle is overstimulated, which leads to an erratic involuntary contraction — a cramp. In addition, muscles which span two joints, like the calves, are particularly susceptible to cramps. Apparently, since they can be placed in a very shortened state (relaxed) but still contract, the relaxing sensors can easily become overwhelmed by the contracting sensors.

The treatment for a muscle cramp has long been to stretch the affected muscle, and stretching is endorsed by proponents of this new theory. The effect of stretching the muscle is to increase the tension in the muscle, resulting in activity of the structures which causes the muscle to relax. Since fatigue appears to be an important factor leading to cramps, it seems logical to take precautions to address things that lead to lingering fatigue. Avoid overtraining, stay well hydrated and properly fueled before, during and after workouts, and take care of your muscles through stretching, massage and whirlpools. Further research leading to an understanding of why fatigue impacts the activity of the contraction and relaxation structures may provide further insight into how to avoid cramps. Until then, stretching remains the prescribed treatment when you get a cramp.

Painful Side Stitches

The “side stitch” refers to that wellknown abdominal pain that recently has been labeled exercise-related transient abdominal pain.(4) Research indicates that about 70% of regular runners have experienced a side stitch within the past year.(4)

Theorized mechanisms responsible for side stitches have mostly concentrated on either lack of blood flow to the diaphragm or stress placed on the ligaments that attach the abdominal organs to the diaphragm. (5) The second theory, which has been accepted as the most credible explanation of stitches, asserts that the jolting motion associated with activities like running is responsible for strain on the supportive ligaments of the abdominal organs.

Questions arose about the validity of that theory when recent research indicated that some people experience stitches extremely low in the abdomen, far removed from the site of the ligaments under the diaphragm.(4) Furthermore, a high percentage of swimmers claim to experience side stitches, even though swimming is an activity not characterized by jolting actions.4 These findings have resulted in the development of an alternative theory by researchers at the University of Newcastle, Australia to explain the mechanism responsible for the side stitch.

The new theory suggests that the tissue responsible for the pain is the lining of the abdominal organs which attaches to the abdominal wall — called the parietal peritoneum.

Lining the inside front of the abdominal cavity are two layers of membrane. The visceral peritoneum covers the abdominal organs, and the parietal peritoneum attaches to the abdominal wall. Contained between the two layers is a small volume of lubricating fluid which usually allows the two surfaces to move freely without rubbing. The characteristics of stitch, being described as a highly localized pain that can occur at any position within the abdomen, points to the membrane attaching to the abdominal wall — the parietal peritoneum — as potentially responsible for the pain. Consistent with this theory, this membrane is sensitive to movement when irritated. Additionally, this membrane (especially the part that extends up under the diaphragm) and the tip of the shoulder share some of the same nerves, which gives rise to the referred shoulder-tip pain commonly experienced by people who have a side stitch.

Exactly what causes this abdominal membrane to become irritated is being explored, but one explanation may be friction between the two layers of the membrane. Friction could result from abdominal organs such as the stomach being distended and pushing the two surfaces more firmly together, as occurs following a meal. Alternatively, the quantity of the lubricating fluid between the two layers may decrease as a result of a reduction in blood flow (the source of the fluid) to the abdomen during exercise or increased diaphragm movement associated with exercise. These facilitate the removal of the fluid from between the two membranes.

The new theory may lead to the development of innovative techniques for preventing stitches, but presently it seems that not eating two to three hours before exercise is the most effective procedure. Additionally, extremely sugary foods and drinks may be particularly potent for evoking stitches.(5) Researchers from the University of Otago, New Zealand, found that sports drinks resulted in fewer symptoms of stitch than other solutions, including water. Being well hydrated has also been identified as important in the avoidance of stitches. However, when consuming drinks during exercise small, regular volumes are preferable to larger, less frequent ones.(5,6)

1. Kantarowski et al. (1990). Cramping studies in 2600 endurance athletes. Medicine and Science in Sports and Exercise. 22 (suppl. 4): S104.
2. Schwellnus et al. (1997). Aetiology of skeletal muscle ‘‘cramp’’ during exercise: a novel hypothesis. Journal of Sports Sciences. 15: 277-285.
3. Maughan (1986). Exericse-induced muscle cramp: a prospective biochemical study in marathon runners. Journal of Sports Sciences. 4: 31-34.
4. Morton & Callister (1998). Prevalence and characteristics of ‘‘stitch’’ in different exercise modalities. Medicine and Science in Sports and Exercise. 30 (suppl. 1086): S192.
5. Plunkett & Hopkins (1998). Investigation of the side pain “stitch” induced by running and fluid ingestion. Medicine and Science in Sports and Exercise.
6. Kanter (1997). What causes the runner’s stitch? Sports Science Update. Gatorade Sports Science Institute Web site, 3(1).

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