Inadequacy of calcium supplements to normalize muscle calcium deficiency in healthy subjects during prolonged hypokinesia

Objective We investigated the effect of hypokinesia (diminished movement) on muscle calcium (Ca2+) content with and without Ca2+ supplementation and Ca2+ loss with different muscle Ca2+ deficiency; muscle Ca2+ content, plasma Ca2+ level, and Ca2+ loss were measured. Methods Studies were performed in 40 physically healthy male volunteers during a pre-experimental period of 30 d and an experimental period of 364 d. Subjects in equal numbers were assigned to one of four groups: unsupplemented active control subjects (UACSs), unsupplemented hypokinetic subjects (UHKSs), supplemented active control subjects (SACSs), and supplemented hypokinetic subjects (SHKSs). A daily supplementation of 0.7 mmol of calcium lactate per kilogram of body weight was given to SACSs and SHKSs. Results Muscle Ca2+ content decreased, and plasma Ca2+ concentration and Ca2+ loss in urine and feces increased (P < 0.05) in the SHKS and UHKS groups compared with their pre-experimental values and the values in their respective active control groups (SACS and UACS). However, muscle Ca2+ content decreased more, and plasma Ca2+ concentration and Ca2+ loss increased more (P < 0.05) in the SHKS group than in the UHKS group. Conclusion Muscle Ca2+ deficiency is more evident when Ca2+ intake is higher and Ca2+ loss is more exacerbated with higher than with lower muscle Ca2+ deficiency, indicating that muscle Ca2+ deficiency during prolonged hypokinesia is due to an inability of the body to use Ca2+ but not to a Ca2+ shortage in the diet.