MAGNESIUM LOADING EFFECT ON MAGNESIUM-DEFICIENCY IN ENDURANCE-TRAINEDSUBJECTS DURING PROLONGED RESTRICTION OF MUSCULAR-ACTIVITY

The aim of this study was to evaluate the effect of magnesium (Mg) loa ding (10.0 mg Mg/kg body wt) and daily Mg supplements (5.0 mg Mg/kg bo dy wt) on Mg deficiency shown by increased and not by decreased serum Mg concentration during hypokinesia (decreased km number/d). The studi es were done during 30 d of prehypokinesia and 364 d of hypokinesia (H K) periods. Forty endurance-trained volunteers aged 22-26 yr with a pe ak VO2 max of 66.3 mL . kg(-1) min(-1) and with an average 15.0 km/d r unning distance were chosen as subjects. They were equally divided int o four groups: 1. Unsupplemented ambulatory control subjects (UACS). 2 . Unsupplemented hypokinetic subjects (UHKS). 3. Supplemented hypokine tic subjects (SHKS). 4. Supplemented ambulatory control subjects (SACS ). The SHKS and SACS groups took daily 5.0 mg elemental Mg/kg body wt and subjected to Mg loading (10.0 mg Mg/kg body wt). Both the SHKS and UHKS groups were maintained under an average running distance of 4.7 km/d, whereas the SACS and UACS groups did not experience any modifica tions to their normal training routines and diets. During the prehypok inetic and hypokinetic periods, excretion of Mg in feces and urine, co ncentration of Mg in serum, and Mg balance were measured, urinary and serum sodium (Na), potassium (K), and calcium (Ca) were also determine d. In both SHKS and UHKS groups, fecal Mg loss, urinary excretion of e lectrolytes, and serum concentrations of electrolytes increased signif icantly (p less than or equal to 0.05) when compared with the SACS and UACS groups. During Mg loading tests, urinary and fecal Mg excretion was also greater in the SHKS and UHKS groups than in the SACS and UACS groups. Throughout the study, Mg balance was negative in the SHKS and UHKS groups, whereas in the SACS and UACS groups, Mg balance was posi tive. It was concluded that significant losses of Mg occurred in the p resence of negative Mg balance and Mg deficiency in endurance-trained subjects during prolonged exposure to HK, daily mg supplements, and Mg loading tests. This suggests that Mg is not entering or being retaini ng by the bones and cells of many tissues where most Mg is deposited n ormally, resulting in Mg deficiency as was shown by the increased seru m Mg concentration.