Muscle water and electrolytes following varied levels of dehydration in man

TLDR

The study aimed to evaluate how dehydration alters plasma and muscle water and electrolyte (Na⁺, K⁺, Cl⁻, Mg²⁺) content in eight men exercising in 39.5 °C heat. Blood, urine, and muscle biopsies were collected before exercise and after body‑weight losses of 2.2 %, 4.1 %, and 5.8 %. Plasma and muscle water decreased 2.4 % and 1.2 % per percent body‑weight loss, muscle Na⁺ and Cl⁻ remained unchanged while Mg²⁺ fell 12 % at 5.8 % dehydration, intracellular K⁺ rose 7.2 % and 10.6 % at 2.2 % and 4.1 % dehydration, and these shifts did not markedly alter resting membrane potential.

Abstract

In an effort to assess the effects of dehydration on the content of water and electrolytes (Na+, K+, Cl-, and Mg2+) in plasma and muscle tissue, eight men exercised in the heat (39.5 degrees C, 25%). Blood urine, and muscle biopsy samples were obtained before exercise and after the subjects had reduced their body weight by 2.2, 4.1, and 5.8%. On the average, plasma and muscle water (H2Om) contents were found to decline 2.4 and 1.2% for each percent decrease in body weight. Muscle sodium (Na+m) and chloride (Cl-m) content remained unchanged with dehydration, while muscle magnesium (Mg2+m) declined 12% as a result of the 5.8% dehydration. In terms of intracellular concentrations, K+i increased 7.2 and 10.6% at the 2.2 and 4.1% dehydration levels, respectively. Calculations of the resting membrane potential suggest that the water and electrolyte losses observed in these studies do not significantly alter the excitability of the muscle cell membrane.