Sudden painful muscular contractions that last a few seconds or much longer are muscle cramps. It's those electrolytes -- salt and minerals -- in your body that get a bit out of kilter and cause your muscles to contract. Muscle cramping during or after exercise has been linked to loss of electrolytes and dehydration from sweating but it turns out this is not the primary cause of exercise associated muscle cramps.
Salt and Minerals
Sodium, potassium, magnesium, calcium, phosphate and chloride are important electrolytes that are absorbed from your digestive tract and excreted through your kidneys and sweat glands. Your electrolytes are in balance when the gains and losses of each individual electrolyte are equal. This means your body is balancing the rate of absorption and excretion of each electrolyte so there is not a net gain or net loss of each electrolyte. Electrolyte balance is important for water balance and muscle function.
History of Causes
Abnormal changes of electrolyte levels and dehydration was first identified in hospitals and clinics. Patients diagnosed with certain medical conditions had symptoms of severe skeletal muscle cramping. Blood test results of these patients showed abnormal electrolyte levels and dehydration. Abnormal electrolyte levels in the blood can cause muscle spasms, muscle cramps and muscle weakness. The idea that muscle cramps might be associated with exercise came from these clinical diagnoses. That exercise associated muscle cramps might be caused by dehydration and loss of electrolytes. A body of research began focusing on dehydration, abnormal electrolyte levels, environmental stress and exercise fatigue as probable causes for exercise associated muscle cramps. This background research is published in the "British Journal of Sports Medicine" in August 2004 and the "Journal of Athletic Training" in April 2005.
Medications and Medical Conditions
Certain medications and medical conditions have been known to cause nightly muscle cramps in older people. A scientific review published in the "Postgraduate Medical Journal " in October, 2002 indicates that drugs prescribed for pain, heartburn and peptic ulcers, high blood pressure, lowering cholesterol, and stabilizing moods can cause leg cramps. Medical conditions known to cause muscle cramps noted in this scientific review are kidney disease, thyroid disease, and other medical conditions that can lower your magnesium, potassium and calcium levels. These electrolytes have the greatest effect on skeletal muscle function.
Exercise
Research Scientists Alan P. Jung and colleagues conducted a clinical study to address the dehydration theory and the electrolyte theory in college-aged men with a history of exercise associated muscle cramps. Thirteen men participated in two parts of this study. In part one of the study, 13 men drank a carbohydrate-electrolyte beverage while performing several exercise tests in a hot environment. In part two of the study, 13 men in a normal state of hydration performed several exercise tests in a hot environment and were not allowed to consume any fluids during exercise testing. The results showed that men had muscle cramps in both parts of the study which means that drinking fluids does not prevent muscle cramping during exercise. One interesting finding is that it took longer for men to cramp drinking fluids, about 37 minutes than without fluids, about 15 minutes. Researchers conclude that dehydration and electrolyte imbalance is not the cause of muscle cramps. That muscle fatigue from heat and endurance is most likely the cause of muscle cramping. Their results are published in the "Journal of Athletic Training," in 2005.
Endurance Exercise
Professor Martin Schwellnus and colleagues conducted a cohort study of 72 long-distance road race runners to look for any changes in their electrolyte levels and hydration status before and after the race. In a cohort study, researchers followed a group of people over a period of time. Runners in this cohort study were divided into two groups -- cramping and non-cramping. Blood samples were taken from both groups of runners before the race, immediately after the race and then again 60 minutes after the race to determine their electrolyte levels and hydration status. The results did not show any meaningful differences in each electrolyte level or hydration status between the two groups. Researchers report that their results are similar to prior research studies, however, the clinical studies completed so far are few and too small to make any final conclusions. This study is published in the "British Journal of Sports Medicine" in August 2004. The findings from this study and prior studies will help scientists explore other causes for skeletal muscle cramps associated with exercise.
References
- Postgraduate Medical Journal; Nocturnal Leg Cramps in Older People; J.V. Butler et al., 2002
- British Journal of Sports Medicine; Serum Electrolyte Concentrations and Hydration Status Are not Associated With Exercise associated Muscle Cramping (EAMC) in Distance Runners; Martin Schwellnus, Ph.D., et al., 2004
- Journal of Athletic Training; Influence of Hydration and Electrolyte Supplementation on Incidence and Time to Onset of Exercise-Associated Muscle Cramps; Alan P. Jung, Ph.D., et al., 2005
