In vivo measurement technique of 40K as an indicator of the amount of skeletal muscle tissue in the human body.

Potassium is an essential element for human metabolism. It is present in all living cells, predominantly in the skeletal muscle tissue. The energy of the 40K photon and its uniform distribution within the human body allow its in vivo measurement. Subjects of both sexes were monitored at the whole-body counter of the IRD facility for the evaluation of 40K body burden, being divided into two groups: (1) subjects who do not exercise routinely, and (2) subjects who do exercise routinely. The average values found for potassium mass and potassium concentration in group 1 were 99 +/- 17 g of K and 1.3 +/- 0.2 g of K kg(-1) of body mass, respectively, and in group 2 the average values found for potassium mass and potassium concentration were 118 +/- 33 g of K and 1.6 +/- 0.2 g of K kg(-1) of body mass, respectively. The comparison between average values for potassium mass and concentration shows a significant statistical difference.