CD36-deficient congenic strains show improved glucose tolerance and distinct shifts in metabolic and transcriptomic profiles.

Deficiency of fatty acid translocase Cd36 has been shown to have a major role in the pathogenesis of metabolic syndrome in the spontaneously hypertensive rat (SHR). We have tested the hypothesis that the effects of Cd36 mutation on the features of metabolic syndrome are contextually dependent on genomic background. We have derived two new congenic strains by introgression of limited chromosome 4 regions of SHR origin, both including the defective Cd36 gene, into the genetic background of a highly inbred model of insulin resistance and dyslipidemia, polydactylous (PD) rat strain. We subjected standard diet-fed adult males of PD and the congenic PD.SHR4 strains to metabolic, morphometric and transcriptomic profiling. We observed significantly improved glucose tolerance and lower fasting insulin levels in PD.SHR4 congenics than in PD. One of the PD.SHR4 strains showed lower triglyceride concentrations across major lipoprotein fractions combined with higher levels of low-density lipoprotein cholesterol compared with the PD progenitor. The hepatic transcriptome assessment revealed a network of genes differentially expressed between PD and PD.SHR4 with significant enrichment by members of the circadian rhythmicity pathway (Arntl (Bmal1), Clock, Nfil3, Per2 and Per3). In summary, the introduction of the chromosome 4 region of SHR origin including defective Cd36 into the PD genetic background resulted in disconnected shifts of metabolic profile along with distinct changes in hepatic transcriptome. The synthesis of the current results with those obtained in other Cd36-deficient strains indicates that the eventual metabolic effect of a deleterious mutation such as that of SHR-derived Cd36 is not absolute, but rather a function of complex interactions between environmental and genomic background, upon which it operates.

[Multicenter multidisciplinary training program for chronic low back pain: French experience of the Renodos back pain network (Réseau Nord-Pas-de-Calais du DOS)].

OBJECTIVES: To evaluate the short- and long-term effectiveness of the multidisciplinary training program (MTP). To show the benefits which the network organization brings to the treatment of chronic low back pain (CLPB). METHODS: The member centres of the Renodos back pain network included 748 subjects in the MTP. The centres used a common evaluation protocol including pain and quality of life visual analogue scales (VAS), fingertip-to-floor distance (FFD), muscle isometric endurance tests, Roland-Morris Disability Questionnaire (RDQ), the Dallas Pain Questionnaire (DPQ) and the Hospital Anxiety Depression (HAD) scale. Measurements were carried out before (T0) and immediately after (T1) the intervention, and at the 3-, 6-, 12-month (T3, T6, T12) follow-up visits. RESULTS: Statistically discernible improvement occurred for men and women on every outcome measure from before to after the MTP (T0-T1, p<0.0001). This improvement obtained at T1 was maintained for most of the outcome measures throughout the 12-month follow-up. However, the pain intensity and isometric muscle endurance times showed significant negative evolution. Significant differences between genders were found for the trunk flexibility measurement (FFD), the isometric endurance time of the quadratus lumborum muscle, the RDQ and the HAD depression. There was no time-gender interaction. CONCLUSION: The MTP was effective in reducing back pain intensity, functional disability, symptoms of anxiety and depression and in improving quality of life, flexibility and isometric muscle endurance time. It was possible to propose the MTP to both men and women. A network organization effectively contributes to the harmonization of evaluation methods and brings coherence to the treatment of CLBP patients.

Mapping of quantitative trait loci (QTL) of differential stress gene expression in rat recombinant inbred strains.

OBJECTIVE: Stress has been shown to be a major environmental contributor to cardiovascular diseases through its effects on blood pressure variability and cardiac function. The cellular stress response is characterized by the expression of specific heat stress genes (hsps), under the transcriptional control of heat shock transcription factors (HSTFs). The levels of hsp mRNA depend on the severity of the stress, with hstf1 acting as a stress sensor. The aim of this work was to evaluate the genetic contribution of the variability in hsp expression, and to identify its putative quantitative trait loci (QTL). METHODS: Twenty recombinant inbred rat strains (RIS) were studied. The animals underwent a standardized, identical 1 h immobilization stress in restraint cages, followed by 1 h of rest before sacrifice. Total RNA was extracted from the heart kidneys and adrenals, and the mRNA levels of hsp27, hsp70, hsp84, hsp86 and hsp105 were measured. The strain distribution pattern (SDP) of hsp expression was correlated with that of 475 polymorphic markers distributed throughout the RIS genome. A polymorphism of rat hstf1 in RIS was used for its mapping in RIS. RESULTS: Despite an identical stress being applied to all strains, hsp expression showed up to a 1 2-fold gradient with little intra-strain variability, indicative of a strong genetic contribution to the trait Heritability ranged from 50 to 77% for most hsp genes in the three target organs. The continuous SDP of stress gene expression indicated the polygenic nature of the trait A common locus on chromosome 7 (at D7Cebrp187s3 marker) was consistently associated with all hsp expression in most of the organs [with a likelihood of odds (LOD) score of 3.0 for hsp27 expression]. We have mapped rat hstf1 on chromosome 7 at the same locus. Finally, the D4Mit19 marker was significantly associated with hsp84 expression in the heart (LOD score of 3.1). CONCLUSION: Two loci were linked with the differential expression of HSPs in response to immobilization stress in target organs of RIS. The chromosome 7 locus unveiled for all HSPs could explain up to 42% of the observed inter-strain variability of hsp levels in response to stress. We propose hstf1 as a positional candidate at this locus.

Differential effect of knee extension isometric training on the different muscles of the quadriceps femoris in humans.

This study determined the effects of a short period of knee isometric training on the quadriceps muscles accessible to surface electromyography (EMG). For this purpose, a training (n = 9) and a control (n = 7) group were tested on five identical occasions at 1 week intervals during 4 weeks. The training group exercised three times a week by making isometric knee extensions at 80% of the maximal voluntary contraction (MVC). During the test sessions, maximal and submaximal torque and associated activations of the rectus femoris (RF), vastus lateralis (VL) and vastus medialis (VM) muscles were analysed. As a result of training, differences between MVC values of the two groups were highly significant (P<0.001), whereas only RF-EMG showed significant differences (P<0.05). The VL and VM did not present any significant changes in maximal activation. The EMG torque relationships were analysed individually before and after the training period. For the control subjects, EMG-torque relationships did not present significant changes while for the training group, these relationships showed a significant increase in RF, VL, and VM maximal activation in 6, 6 and 4 subjects, respectively, and a significant decrease in 1, 2 and 5 subjects, respectively. In almost all cases, a significant downward shift of the relationship was observed. This study confirmed that the parts of the quadriceps muscle tested present different adaptation capacities and demonstrate inter-individual variability in the strategies used to enhance muscle strength. In conclusion, to analyse the neural effects resulting from training in a large and compartmentalized muscle like the quadriceps femoris, it is desirable to take into account each muscle independently. Moreover, we suggest that overall results obtained from the experiment population should be completed by an analysis on individuals.

Validity of the Université de Montréal Track Test to assess the velocity associated with peak oxygen uptake for adolescents.

BACKGROUND: The purpose of the study was to test the ability to determine the velocity associated with peak oxygen uptake for adolescents by means of a simple field test, the Université de Montréal Track Test (UMTT). METHODS: Fifteen adolescents, 13.4 +/- 1.0 years, performed two maximal field tests where oxygen uptake and heart rate were continuously monitored. The first test (graded field test, first stage 8 km.h-1, increment 1.5 km.h-1, duration 3 min) allowed the subjects to reach a steady-state oxygen uptake. Then, the velocity associated with peak oxygen uptake was calculated from the ratio between peak oxygen uptake above resting level to energy cost of running. The calculated velocity was kept as the criterion velocity. For the second test (UMTT, first stage 8 km.h-1; increment 1 km.h-1; duration 2 min), the velocity measured at the last completed stage was retained. RESULTS: The measured peak oxygen uptake for the graded field test (51.8 +/- 6.5 ml.kg-1.min-1) and for the UMTT (51.0 +/- 7.9 ml.kg-1.min-1) were not significantly different. The calculated velocity (12.9 +/- 1.0 km.h-1) and the measured velocity (12.7 +/- 0.9 km.h-1) were not significantly different and were significantly correlated (r = 0.80, p < 0.001). CONCLUSIONS: It was concluded that, for adolescents, the velocity measured at the last completed stage of the UMTT allows a valid estimation of the velocity associated with peak oxygen uptake.

Comparison of maximal aerobic speed as assessed with laboratory and field measurements in moderately trained subjects.

In order to compare the Maximal Aerobic Speed (MAS) evaluated with different methods, eleven male physical education students (22.2 +/- 3.0 years) were submitted to a maximal treadmill protocol and to the Université de Montréal Track Test (UMTT). Four methods were used to calculate MAS. After treadmill measurement of VO2max, MAS was calculated (MAS_calc) by the following formula: MAS_calc = (VO2max - 0.083)/C, where VO2max is the maximal oxygen uptake (ml.kg-1.s-1) and C the energy cost of running (ml.kg-1.m-1). The extrapolated MAS (MAS_ex) was obtained from the measured VO2max and by extrapolation of the VO2 versus speed relationship. The MAS for treadmill measurement (MAS_tr) and for UMTT (MAS_UMTT) were the velocities at the last completed stages. The average MAS_calc (4.71 +/- 0.48 m.s-1), MAS_ex (4.62 +/- 0.48 m.s-1), MAS-tr (4.75 +/- 0.57 m.s-1) and MAS_UMTT (4.64 +/- 0.35 m.s-1) were not significantly different and were significantly correlated, between 0.85 (MAS_ex vs MAS_UMTT) and 0.99 (MAS_calc vs MAS_tr), with p < 0.001 in both cases. MAS measurements were significantly correlated to measured VO2max but independent of C.

Musculo-articular modelling of the triceps brachii.

With the aim of proposing modelling equations for the length, force and shortening velocity of the triceps brachii, an X-ray and biomechanical study was carried out on the elbow joint. Two series of three upper right limbs removed from cadavers were used. It allowed us to situate the articular rotational axis of the elbow and to modelise the lever arm of the muscle group of the elbow extensors. Eight superimposed X-ray films with opaque markers at different articular angles show that the rotational axis of the elbow is different from the epitroch-lea-epicondyle axis, commonly localised by palpation and used as such in functional and biomechanical explorations. This rotational axis of the elbow, situated in the trochlea, is fixed at the centre of the articular range and moves noticeably to both extremities of this range. Biomechanical study, based on measurement of internal and external torques established using an overload, allowed us to modelize the lever arm of the triceps brachii between 0 and 2.44 radians, according to length of the ulna. The applications concerning length, force and shortening velocity of the triceps brachii are described. This method of modelling is applicable to other joints and muscle groups.

Effect of a 12-week training programme on Maximal Aerobic Speed (MAS) and running time to exhaustion at 100% of MAS for students aged 14 to 17 years.

The aims of this study were to use the Maximal Aerobic Speed (MAS) to set training intensities for aerobic training and to measure the effects of two different training programmes on MAS and on the running time to exhaustion at 100% of MAS (Tlim) for 121 students aged 14 to 17 years. The MAS was measured using the Université de Montréal Track Test (UMTT). This measurement was found reproducible for males (r = 0.93) and females (r = 0.68). The Students followed a 12-week training programme of one weekly training session. The MAS and the Tlim were measured the weeks before and after training. Two training programmes were proposed (intense training programme and moderate training programme). These training programmes differed by the ratio between continuous exercises (85% of MAS) and intermittent exercise (between 90% and 120% of MAS). For the moderate training programme, the ratio between continuous and intermittent exercises was greater than for the intensive training programme. Twenty subjects served as control group. The students MAS and Tlim (mean +/- SD) were respectively 13.7 +/- 1.6 km.h-1 and 380.5 +/- 91.8 s for the males and 11.3 +/- 1.2 km.h-1 and 347.2 +/- 91.1 s for the females. Our results indicated that only the subjects of the intense training group improved their MAS: + 5.7% for the males (p < 0.001) and + 5.4% for the females (p < 0.001). In neither case was Tlim significantly improved with training. In conclusion, we can notice that MAS is a pertinent criterion to set training intensities for aerobic training and that a weekly training session over 12 weeks is sufficient to moderately improve the MAS of initially untrained students.

Comparison of two field tests to estimate maximum aerobic speed.

The measurement of maximal aerobic speed (MAS) and the prediction of maximal oxygen uptake (VO2 max) by means of field tests were carried out on 17 students studying physical education. The subjects underwent a continuous multi-stage track test (Léger and Boucher, 1980), shuttle test (Léger et al., 1984) and VO2 max measurement on a treadmill. The VO2 max values estimated using the track test (56.8 +/- 5.8 ml kg-1 min-1) were not significantly different from the values measured in the treadmill test (56.8 +/- 7.1 ml kg-1 min-1), but were higher than those estimated using the shuttle test (51.1 +/- 5.9 ml kg-1 min-1). The maximal nature of the tests was checked by measurement of heart rate and lactate concentration, taken within 2 min post-test. The means of the MAS observed in the track test (15.8 +/- 1.9 km h-1) and in the treadmill test (15.9 +/- 2.6 km h-1) were not significantly different (P > 0.10). The mean of the shuttle test MAS (13.1 +/- 1 km h-1) was significantly lower (P < 0.01) than those of the other tests. However, the MAS of the shuttle test and track test are linked. The equation for linear regression between MAS values in these two tests is MAStrack = 1.81 x MASshuttle -7.86 (r = 0.91), allowing estimation of one of these MAS values when the other is known. Thus these values may be used within diversified training.

Series elasticity in frog sartorius muscle subjected to stretch-shortening cycles.

Changes in stiffness during stretch-shortening cycles were studied by applying prestretches of different rates and amplitudes on the tetanized sartorius muscle of the frog and measuring series elastic component characteristics during a subsequent quick release. Series elastic component stiffness was found to be dependent on the mechanical parameters of the stretching phase, and the so-called 'Cavagna effect' (increase in compliance) was rarely observed. The results are discussed in terms of improvement in muscle efficiency. Thus, an increase in stiffness during force generation will favour a better transmission of force and will reduce the coupling time whereas the opposite evolution during SEC recoil will allow a better release of potential energy.

Series elasticity in frog sartorius muscle during release and stretch.

When a stretch is applied to an isolated muscle during tetanic stimulation, the force developed is higher than the maximal isometric tension (Po). This force puts the series elastic component (SEC) under tension and in a domain which is not well defined in terms of tension-extension curve. In the present work, an attempt was made to determine the stiffness of the SEC for tensions greater than Po, using the sartorius muscle of the frog. For this purpose, rapid releases and stretches of different amplitudes were given during maximal isometric contractions. Plotting normalized tension (P/Po) against normalized length changes (negative or positive extensions, delta L/Lo.10(2] produced a tension-extension curve. The slopes of the linear part of each relationship on both sides of Po indicated an increase in SEC stiffness when the muscle was rapidly stretched. Furthermore, the transient character of the increase in stiffness was studied by measuring SEC stiffness during rapid releases applied at various time intervals after stretches: the muscle was found to be stiffer as the time interval was shorter. The results are discussed in terms of (i) non-linear behaviour of the passive and active parts of the SEC, (ii) enhancement of storage and release of potential energy.