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.

Key words

muscle biopsy - extracellular volume - intracellular volume - plasma