Out of 100 |il of capillary blood of 15 ensigns from the Theresian Military Academy, ionized magnesium was determined with a CCX device (NOVA Biomédical) and CSA Software (PLK, Judendorf-Strassengel, Austria), before and after a 2,400 m run, both before and after an 8 week-long supplementation of 300 mg magnesium per day. It turned out that Mg changes in blood mainly follow two interlinked phenomena: 1. Mg substitution leads to more controlled Mg input into the blood after the same sporting challenge, and 2. Mg clearance is strictly proportional to Mg concentration in blood. Varying permutations of those two points explain the entire performance of Mg dynamics in blood, including the hitherto unexplained paradox decrease of blood Mg during substitution [1,2].