Muscle Water and Electrolyte Distribution During Prolonged Exercise

Abstract

In an effort to describe the changes in water and electrolyte contents of active and inactive muscles during prolonged effort, seven healthy men were studied during 120 min of cycling. Needle biopsy samples were taken from the deltoid (inactive) and vastus lateralis (active) muscles before, at 10 and 120 min of exercise, and 30 min after exercise. Water and electrolyte contents of blood and active muscle tissue showed a significant change with the onset of exercise, while the inactive muscle was unaffected. As a consequence of the exercise, the subjects lost an average of 2.40 liters of body water, 93 mEq Na+, 22 mEq K+, 95 mEq Cl-, and 5 mEq Mg++. These water and electrolyte losses were not detectable in the muscle tissue sampled at the end of exercise or after 30 min recovery. Based on the loss of Cl-, body weight and plasma volume, extracellular, intracellular, and total body water volumes were calculated to decrease approximately 9%, 3% and 7.5%, respectively, at the end of the exercise. These observations confirm earlier findings that exercise and electrolyte losses in sweat and urine do not alter the calculated membrane potential of active and inactive muscle.

Promotion of Healthy Weight-Control Practices in Young Athletes

“…20 -24 After 2 to 3 days of dehydration, replacement of intracellular fluids takes 48 hours. 25 Athletes and coaches in weightclass sports often harbor a belief that weighing in at the lowest possible weight will maximize strength-to-weight ratio and increase an athlete's competitive advantage. 4,6 However, inadequate hydration has been shown to decrease athletic performance; aerobic function is impaired more than anaerobic performance.…”

The Effect Of Sodium And Carbohydrate In A Rehydration Food On Subsequent Exercise Performance

“…In one study, plasma volume (PV) decreased 12% in the first 10 min of endurance exercise. Despite heavy sweating for an additional 110 min of exercise, PV only dropped additional 3.6% (9,10). In a related study, Costill et al (9) observed an increase (8%) in water content in active muscles during the first minutes of exercise, with an equivalent decrease in PV.…”

Human Water and Electrolyte Balance

“…10,17 As a result, relatively less intracellular fluid is lost after diuretic administration, since there is not an extracellular solute excess to stimulate redistribution of body water. In contrast, several studies 13,18,19 report substantial decreases in skeletal muscle intracellular water content following prolonged exercise without fluid replacement, presumably the result of water released with the breakdown of muscle glycogen. Exercise-induced hypohydration may therefore result in a greater intracellular water loss than simple sweat-induced hypohydration (passive thermal dehydration).…”