Define measuring body composition- Total body potassium?
It applies the' concept  that body  cells contain a  constant amount of  potassium and  that  its measurement is therefore an  indicator  of  lean body  mass. The body potassium can  be measured by  injecting a radioisotope,  K42, allowing time for  its  equilibration within  the cells, and  then  withdrawing  samples  for analysis. Another technique involves the measurement of the naturally
Occurring K40 in the body with a low level whole body  scintillation counter.  Since K40 accounts for 0.012 percent of naturally-occurring potassium, the total Body potassium can be calculated.