Magnesium Research 2015; xx (x): 1-7 ORIGINAL ARTICLE Magnesium and phase angle: a prognostic tool for monitoring cellular integrity in judo athletes Catarina N. Matias 1, 3 , Cristina P. Monteiro 2, 3 , Diana A. Santos 1, 3 , Fátima Martins 4 , Analiza M. Silva 1, 3 , Maria J. Laires 3 , Luís B. Sardinha 1, 3 1 Exercise and Health Laboratory, CIPER, Faculty of Human Kinetics, University of Lis- bon, Estrada da Costa, 1499-002 Cruz-Quebrada, Portugal; 2 Physiology and Biochemistry of Exercise Laboratory, CIPER, Faculty of Human Kinetics, University of Lisbon, Estrada da Costa, 1499-002 Cruz-Quebrada, Portugal; 3 CIPER - Interdisciplinary Center for the Study of Human Performance, Faculty of Human Kinetics, University of Lisbon, Estrada da Costa, 1499-002 Cruz-Quebrada, Portugal; 4 Immunology Laboratory, National Institute of Health Dr. Ricardo Jorge, Avenida Padre Cruz, 1649-016 Lisboa, Portugal. Correspondence: Catarina Nunes Matias Exercise and Health Laboratory Faculdade de Motricidade Humana Universidade de Lisboa, Estrada da Costa 1499-002 Cruz-Quebrada Portugal <cmatias@fmh.ulisboa.pt> Abstract. Adequate magnesium (Mg) levels play a vital role in membrane excitability, cell contractility and metabolism, being a key nutrient for sustain- ing appropriate muscular contraction and performance levels in athletes. Phase angle (PhA), assessed by bioimpedance analysis (BIA), has been reported to be positively associated with most nutritional markers and is an indicator of membrane integrity and water distribution between intra- and extracellular spaces. The aim of the present study was to verify the association between Mg status and PhA as a predictor of cellular health, in a sample of judo athletes from a period of weight stability to prior to competition. Judo athletes (n = 20) from the national team were evaluated on two occasions: during a period when body weight was stable (M1), and prior to competition (M2). Changes between these occasions were calculated as M2-M1. PhA was obtained by bioelectrical impedance spectroscopy at a frequency of 50 KHz. Mg was measured in serum and red blood cells (RBC) by atomic absorption spectrophotometry, and Mg in the diet was assessed from a 24-h diet record over a seven-day period, after an assessment of body composition. PhA did not differ from M1 to M2. Changes in PhA were directly associated with changes in serum (r = 0.62, p = 0.004) and RBC Mg (r = 0.45, p = 0.048). Q1 This association was independent of weight changes between assessments, but when adjusted for Mg intake changes, only the association between PhA and serum Mg remained significant. These results highlight that in elite athletes PhA may be an indirect indicator of muscular function. Key words: magnesium, phase angle, athletes, cellular health Bioelectrical impedance analysis (BIA) is a rapid, safe, and non-invasive method for estimat- ing body composition and nutritional status [1, 2]. Nevertheless this method depends on predictive equations specific for each population [3]. Phase angle (PhA) is a measurement of interest obtained from BIA because it is independent of body height and weight, as it is calculated as the arctangent of the directly measured reactance-to-resistance ratio. PhA has been reported to be positively doi:10.1684/mrh.2015.0389 1 To cite this article: Matias CN, Monteiro CP, Santos DA, Martins F, Silva AM, Laires MJ, Sardinha LB. Magnesium and phase angle: a prognostic tool for monitoring cellular integrity in judo athletes. Magnes Res 2015; xx(x): 1-7 doi:10.1684/mrh.2015.0389