Dietary potassium and heavy exercise: effects on muscle water and electrolytes

Eight men were studied during two 4-day exercise-dietary regimens, once under a control diet (80 mEq K+/day) and again with a diet low in K+ (25 mEq/day). Muscle K+ increased 5 to 6% as a result of the two exercise-dietary regimens, while no change was observed for muscle Na+ or Mg++. Plasma volume increased throughout the 4 days of each exercise-diet sequence, with the low K+ regimen resulting in the largest plasma volume gain (+15%) and a marked reduction in urinary K+ excretion. Despite the losses of K+ in sweat and the low K+ intake, there was a relatively small decrease in total body K+ content (less than 2% of body content). Based on these measurements of extracellular (plasma) and tissue (muscle) water and electrolytes, we have concluded that in combination with 4 days of heavy exercise and sweating, a low K+ diet will not significantly diminish the total body K+ content.