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Texte intégral de l'article
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Magnesium and strength in elite judo athletes according to intracellular water changes

Magnesium Research. Volume 23, Numéro 3, 138-41, september 2010, Short communication

DOI : 10.1684/mrh.2010.0217


Auteur(s) : Catarina Nunes Matias, Diana Aguiar Santos, Cristina Paula Monteiro, Analiza Mónica Silva, Maria de Fátima Raposo, Fátima Martins, Luís Bettencourt Sardinha, Manuel Bicho, Maria José Laires , Exercise and Health Laboratory, Faculty Human Kinetics, Technical University of Lisbon, Estrada da Costa, Cruz-Quebrada, Physiology and Biochemistry of Exercise Laboratory, Faculty Human Kinetics, Technical University of Lisbon, Estrada da Costa, Cruz-Quebrada, Laboratory of Immunology, Instituto Nacional de Saúde Dr. Ricardo Jorge, Lisbon, Genetics Laboratory, Faculty of Medicine, University of Lisbon, Av a. Prof. Egas Moniz, Hospital de Santa Maria, Cidade Universitária, Lisbon, Portugal.



Auteur(s) : Catarina Nunes Matias1, Diana Aguiar Santos1, Cristina Paula Monteiro2, Analiza Mónica Silva1, Maria de Fátima Raposo2, Fátima Martins3, Luís Bettencourt Sardinha1, Manuel Bicho4, Maria José Laires2

1Exercise and Health Laboratory, Faculty Human Kinetics, Technical University of Lisbon, Estrada da Costa, Cruz-Quebrada
2Physiology and Biochemistry of Exercise Laboratory, Faculty Human Kinetics, Technical University of Lisbon, Estrada da Costa, Cruz-Quebrada
3Laboratory of Immunology, Instituto Nacional de Saúde Dr. Ricardo Jorge, Lisbon
4Genetics Laboratory, Faculty of Medicine, University of Lisbon, Ava. Prof. Egas Moniz, Hospital de Santa Maria, Cidade Universitária, Lisbon, Portugal

Magnesium deficit is associated with muscle weakness, cramps, and structural damage of muscle fibers and organelles [1]. Several studies found that magnesium (Mg) strongly affects muscle performance, such as grip strength and muscle power, probably due to the key role of Mg in energetic metabolism, transmembrane transport and muscle contraction [2-5]. Mg has a direct effect at a cellular level on Na-K ATPase, Na-K-Cl co-transport, K channels, charge screening and permeability effects on membranes [6]. The K-Cl co-transporter is a major determinant of cell dehydration and is inhibited by increasing erythrocyte Mg content [7].

In judo competitions, athletes are divided according to weight. In order to qualify for their respective weight category many athletes undergo impressive weight changes proceeding the events [8], often associated with severe dehydration [9]. Alterations of cellular hydration will influence membrane stretch, membrane bound signalling systems, cytoskeleton, protein phosphorilation, the ionic interior of cells as well as the extent of macromolecular crowding in the cytosol [10] with consequences for the performance of these athletes [11].

The aim of the current study was to understand the impact of magnesium changes on strength from a period of weight stability to prior a competition in a sample of elite judo male athletes who differentially reduced their level of intracellular water.

Material and methods


A total of 20 elite male athletes (age 22.9 ± 2.9 yrs) were evaluated from baseline (period of weight stability and euhydration state) to prior to one of the competitions (approximately one month later). The euhydration state of the athletes was assured at baseline by using the combined information of athletes' post-voiding first-morning body weights and the observation of urine color in the 3 days prior to the first visit, as proposed by Casa et al. [12].

All subjects were informed about the research design and signed a consent form according to the regulations of the Ethical Committee of the Faculty of Human Kinetics, Technical University of Lisbon.


Blood and urine were collected by standard procedures at fast, early in the morning (8 a.m.) using disposable syringe and dry and heparin tubes for blood, and disposable cups for urine. Blood containing tubes were centrifuged at 500 g and red blood cells obtained in the heparin tube were washed 3 times with saline solution, hemolised with destiled water and frozen along with the serum obtained in the dry tube and the urine for posterior analysis.


Magnesium was measured in serum, red blood cells (RBC) and urine by atomic absorption spectrophotometry (GF95Z, Thermo Electron Corporation, S Series, AA Spectrometer, Massachusetts, USA).

Body Composition

Intracellular water

Intracellular water was calculated as the difference between total body water [assessed by deuterium dilution technique using a stable Hydra gas isotope ratio mass spectrometer (PDZ, Europa Scientific, Crewe, UK)] and extracellular water [assessed by the sodium bromide dilution method by high-performance liquid chromatography (Dionex Corporation, Sunnyvale, California)]

Fat-free mass and Fat mass

Dual energy X-ray absorptiometry (QDR-4500, Hologic, Waltham, USA) was used to estimate fat mass and fat-free mass using the equipment's software version 8.21.

Energy and nutrient intakes

Energy and nutrient intakes were assessed from 24h diet records during a 7 day period both at baseline and prior competition. Diet records were analyzed by the software package Food Processor SQL (Food Processor SQL server, Version 10.5, Salem, Oregon, USA).

Maximal and power strength

Maximal handgrip strength was evaluated in the right hand using Jamar Hydraulic Hand Dynamometer (Jamar - Sammons Preston, Bolingbroke, Georgia, USA). Upper-body power output (UBPO) was determined in a bench press machine interfaced to a computer for data analysis and storage (Isocontrol Dinámico V5.1, Madrid, Spain).

Statistical analysis

Subjects were divided according to intracellular water changes (calculated as the percentage difference from baseline values): ICW losses below 2% (n = 9) and ICW losses equal to or above to 2% (n = 11). Data were analyzed with PASW Statistics for Windows version 18.0 (SPSS Inc, an IBM company, Chicago). Variables distribution were tested with Shapiro-Wilk and parametric and non-parametric tests were used for data analysis. Comparison between group means was performed using independent sample T-test or Mann-Whitney-U test. Comparison of intra-group means was performed using the paired-sample T-test or Wilcoxon test. Magnesium parameter percentage changes were correlated with maximal handgrip strength and upper-body power output percentage changes using Spearman correlations in the two groups. For all tests statistical significance was set at p < 0.05.


Mean and standard deviation values of percentage changes in magnesium concentrations, strength, body composition, energy, magnesium and water intake are shown in table 1, according to ICW losses: losses below 2% and losses equal to or above to 2%.

In these athletes, Mg concentrations were within normal ranges, although Mg intake was lower than the Recommended Daily Allowance (RDA).

In the group that had an ICW loss equal to or above to 2%, there was a significant decrease in grip strength and water ingestion. Both groups significantly increased their RBC Mg.

RBC Mg changes were related with grip strength changes only in the group that had a loss of intracellular water equal to or superior than 2%, as shown in figure 1. UBPO changes were not correlated with magnesium changes.
Table 1 Changes (%) in magnesium, body composition, strength, and energy and nutrient intake (mean ± SD).

N = 20

ICW losses below 2% (%)

ICW losses equal to or above 2% (%)

Serum magnesiuma

4.3 ± 8.1

-3.3 ± 6.3

Urinary magnesium

9.5 ± 48.1

12.7 ± 62.4

Red blood cell magnesium

57.0 ± 43.5b

44.8 ± 36.8b

Body weight

-1.26 ± 2.68

-0.93 ± 3.44

Intracellular watera

2.1 ± 3.0

-6.6 ± 3.3b

Percentage fat mass

-1.8 ± 10.8

-0.9 ± 8.4

Fat-free mass

-1.0 ± 2.7

-0.8 ± 2.7


3.3 ± 6.0

-4.6 ± 6.6b

Upper-body powera

6.6 ± 14.0

-4.2 ± 11.1

Total energy intake

-0.04 ± 33.9

-0.16 ± 36.8

Magnesium intake

9.3 ± 50.0

1.7 ± 32.4

Water intake

1.8 ± 75.5

-24.2 ± 29.1b


It is known that sudation and water ingestion reduction are common practices in judo to achieve a target weight [9], which can lead to magnesium deficit, due to high sweat losses [1]. As expected [11, 13], athletes who reduced their ICW significantly decreased their handgrip maximal strength. In this group, we observed a positive correlation between red blood cell Mg changes and handgrip maximal strength changes. This result is in accordance to other studies, since adequate Mg concentrations seem necessary for maintaining optimal muscle performance [2].

In conclusion, intracellular water has been associated with strength reductions [11, 13] though our results suggest that an increase in red blood cell magnesium might attenuate those strength reductions in athletes who decrease their intracellular water compartment. As magnesium losses can be considerable and intake is frequently marginal or insufficient, athletes should consider supplementation, especially during periods of weight reduction.


We would like to express our gratitude to the athletes for their time and effort.

Disclosure and financial support

This work was supported by the Portuguese Foundation for Science and Technology and by the Interdisciplinary Centre for the Study of Human Performance (CIPER).

None of the authors has any conflict of interest to disclose.


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2 Dominguez LJ, Barbagallo M, Lauretani F, Bandinelli S, Bos A, Corsi AM, Simonsick EM, Ferrucci L. Magnesium and muscle performance in older persons: the InCHIANTI study. Am J Clin Nutr 2006; 84: 419-26.

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13 Silva AM, Fields DA, Heymsfield SB, Sardinha LB. Relationship Between Changes in Total-Body Water and Fluid Distribution with Maximal Forearm Strength in Elite Judo Athletes. J Strength Cond Res 2010 (in press).


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