No abstract

Physical activity is known to have an anabolic effect on bone tissue. It has been shown to increase the bone mineral density (BMD) in young adults, as well as in teenagers. But there is little information about the effect of intensive physical activity in childhood, particularly at the prepubertal stage. To examine the influence of an early intensive physical training on BMD, we have studied a group of elite prepubertal girls, at the starting phase of their peak bone mass acquisition. Subjects were engaged either in sport requiring significant impact loading on the skeleton, or in sport without impact loading. Forty-one healthy prepubertal girls took part in this study. The sport group consisted of 10 swimmers (10.5 +/- 1.4 years old) and 18 gymnasts (10.4 +/- 1.3 years old), who had performed 3 years of high-level sport training (8-12 h per week for swimmers, 10-15 h per week for gymnasts). Thirteen girls (10.7 +/- 1 years old) doing less than 3 h per week of physical activity served as a control group. BMD measurements were done using dual-energy X-ray absorptiometry. There was no statistical significant difference between groups as regards age, body height and weight, and body composition. There was no statistical significant difference between swimmers and controls for all the BMD measurements. Mean BMD in gymnasts was statistically higher than in the control group for mid-radius (+15.5%, p < 0.001), distal radius (+33%, p < 0.001), L2-4 vertebrae (+11%, p < 0.05), femoral neck (+15%, p < 0.001) and Ward's triangle (+15%, p < 0.01). Moreover, in gymnasts, BMD at radius, trochanter and femoral neck was above normative values. We conclude that physical activity in childhood could be an important factor in bone mineral acquisition in prepubertal girls, but only if the sport can induce bone strains during a long-term program: gymnastics has such characteristics, unlike swimming. Such acquisition could provide protection against risks of osteoporosis in later life, but this remains debatable.

Magnetic resonance tagging is used to evaluate the dynamic deformation of lines or grids superimposed on the myocardium during the cardiac cycle. From these data, a specific postprocessing procedure provides two kinds of metrics: (a) three orthogonal components of myocardial motion (longitudinal, circumferential, and radial), and (b) rotation and torsion. Strain expresses the local myocardial deformation and is prone to important physiologic heterogeneities. Peak systolic strain is in the range of -15% to -20% for the longitudinal and circumferential components (fiber shortening) and 30%-40% for the radial component (wall thickening). The helical arrangement of myofibers that run in opposite directions at the epicardium and endocardium explains systolic twist (~15°). This torsion may be enhanced during the early stage of several diseases (eg, hypertrophic cardiomyopathy) or in heart failure with a normal left ventricular ejection fraction. Strain is generally impaired in ischemic heart disease and cardiomyopathy, but the most diagnostically significant finding is the early identification of contractile dysfunction on the basis of longitudinal and circumferential strain reduction in patients with apparently preserved systolic function. Thus, strain impairment appears to be a sensitive and promising marker of subclinical disease, with the potential for improving patient management.

In order to compare variability in M-mode echography and MRI in the assessment of left ventricular mass, 20 echogenic patients without evidence of coronary artery disease were investigated. Two MR and two M-echo examinations were performed within 4 days by different trained operators, each unaware of the other's results. M-mode echo was carried out according to Devereux's method, using the 'Penn-Cube' formula. MR protocol included multislice (8 to 12) true, short-axis spin-echo imaging (10 mm thick with a 1 to 3 mm gap) encompassing the entire left ventricle. Planimetry was manually traced with standardized window settings. Correlations between both echographic and both MR measurements showed r = 0.89, SEE = 22.7 g and r = 0.96, SEE = 11.2 g, respectively. Mean inter-study variability was 11 +/- 6.4% and 6.75 +/- 3.8% (P = 0.0021). The threshold value corresponding to the 95th percentile of the variability data was 21.5% for echography and 13.5% for MR. In conclusion, MR appeared to be a significantly more reproducible examination tool, when compared with M-mode echo, for the evaluation of left ventricular mass (variability, 63% higher with echo than with MR). The main practical consequence of this result lies in the reduced number of patients required to demonstrate a significant change in the LVM with MR as compared with echography.

No abstract

Taken together, those results suggest that more fatigable Type II motor units are involved in men, resulting in greater lactic acid and ions accumulations during fatigue. This difference in muscle's metabolic and ionic state could be responsible for a greater reflex-induced decrease of motor units firing rates in men compared with boys. This firing rate decrease could be explained using the "muscular wisdom" hypothesis and would express a nervous command adaptation to sustain a maximal contraction.

We propose a mechanism for A-type antiferromagnetism in orthorombic LaMnO3, compatible with the large Jahn-Teller splitting inferred from structural data. Orbital ordering resulting from Jahn-Teller distortions effectively leads to A-type ordering (antiferromagnetic in the c axis and ferromagnetic in the ab plane) provided the in-plane distorsion Q2 is large enough, a condition generally fulfilled in existing data. PACS:71.70E, 75.10 Dg, 75.30Et, 75.50eE Stoichiometric LaMnO 3 (LMO) is known [1] to be an A-type antiferromagnetic insulator (A-AFMI), where ferromagnetically ordered MnO 2 planes (in the xy direction) have staggered magnetization along the z axis. Upon increasing the temperature a paramagnetic insulating phase (PMI) is reached. On the other hand sufficient hole doping (e.g. by substituting La with Sr or Ca) gives rise via the so-called double-exchange hopping mechanism [2,3] to a low-temperature ferromagnetic metallic phase (FMM) turning into a PMI phase at higher temperature. Not only magnetism determines the main physical properties, in fact both theoretical [4,5] and experimental [6] evidences emphasize the relevance of electron-lattice coupling. Charge and orbital ordering also occur, further showing the competition between various physical mechanisms. Notice that the crucial role of spin and lattice coupling was repeatedly emphasized to account for the properties of the FMM phase and the FMM-PMI transition at finite doping, as well as charge-ordering phenomena. However, this liaison regarded the doubleexchange mechanism for charge tranport, being dynamically dressed by lattice degrees of freedom [4][5][6]. No emphasis was put on the role of static cooperative JahnTeller (JT) deformations in stabilizing specific magnetic structures in the AFMI phase.Here we investigate an approach to the stoichiometric phase of LMO showing that the layered antiferromagnetic structure may result from the interplay between superexchange and JT couplings. Our analysis is alternative to the more qualitative one based on the semicovalent exchange mechanism [7] and is complementary to the superexchange mechanism investigated by Kugel and Khomskii (KK) [8] for perovskites with JT ions. This latter analysis (see also [9]) focused on the interplay between magnetic and orbital ordering within the two e g orbital manifold, assumed degenerate. In particular, basic ingredients were a strong local electron-electron repulsion U , the Hund coupling J H between electrons on the two e g orbitals, and the orbital mixing (described by a mixing angle θ) due to JT distorsion. In the approach of Ref. [8], only e g (spin and orbital) degrees of freedom were considered, and the spin and orbital order were self-consistently determined to lowest order in J H /U . The e g level degeneracy was lifted by superexchange but the JT splitting resulting from the lattice distorsions induced by orbital ordering was not explicitly considered, Only a correction due to a small local JT anharmonicity was introduced. This point of view, considering m...

T1 mapping is now a clinically feasible method, providing pixel-wise quantification of the cardiac structure’s T1 values. Beyond focal lesions, well depicted by late gadolinium enhancement sequences, it has become possible to discriminate diffuse myocardial alterations, previously not assessable by noninvasive means. The strength of this method includes the high reproducibility and immediate clinical applicability, even without the use of contrast media injection (native or pre-contrast T1). The two most important determinants of native T1 augmentation are (1) edema related to tissue water increase (recent infarction or inflammation) and (2) interstitial space increase related to fibrosis (infarction scar, cardiomyopathy) or to amyloidosis. Conversely, lipid (Anderson–Fabry) or iron overload diseases are responsible for T1 reduction. In this pictorial review, the main features provided by native T1 mapping are discussed and illustrated, with a special focus on the awaited clinical purpose of this unique, promising new method.