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Quantitative MRI and phosphorus magnetic resonance spectroscopy ((31)P-MRS) were used to investigate skeletal muscle metabolism in vivo in patients with dermatomyositis (DM) and polymyositis (PM) in order to evaluate the role of mitochondrial abnormalities in the pathogenesis and clinical expression of these conditions. Nine patients with DM (mean age +/- SD, 57 +/- 14 years) and five with PM (42 +/- 12 years) and with age at disease onset 53 +/- 16 and 38 +/- 12 years, respectively, were included in the study together with 18 age-matched controls. Post-exercise (31)P-MRS indices of muscle oxidative metabolism were all impaired in DM and PM. In both groups of patients, the phosphocreatine and adenosine diphosphate recovery half-times were almost twice as long as in controls (P < 0.05 for each variable) and the maximum rate of mitochondrial ATP production was half that found in normal subjects (P < 0.001). The rate of proton efflux from muscle fibres was significantly reduced in DM (P < 0.001) and PM (P = 0.02). The impairment of (31)P-MRS recovery indices in DM and PM patients was similar to that found in a group of 10 patients with a primary mitochondrial disorder that showed a normal proton efflux rate. There was no correlation between the MRS-detectable abnormalities and the degree of inflammation or fatty infiltration of the muscle, as measured by MRI. The in vivo findings in DM and PM patients indicate impaired muscle aerobic function, which, considering the reduced proton efflux, is likely to be secondary to an impaired blood supply. Our results suggest that the abnormal mitochondria seen in some muscle biopsies are unlikely to be the primary cause of the oxidative insufficiency in these patients.

Interindividual variations in skeletal muscle metabolism make comparative analyses difficult. In this study, we have addressed the issue of capturing the variability of metabolic performance observed during muscle exercise in humans by using an original method of normalization.Metabolic changes induced by various kinds of exercise were investigated using 31P magnetic resonance spectroscopy (MRS) at 4.7 T in 65 normal subjects (23 women and 42 men) and 12 patients with biopsy-proven muscular disorders. Large variations in the extent of PCr breakdown and intracellular acidosis were recorded among subjects and exercise protocols. For all the data pooled, the amplitude of mechanical performance accounts for 50% of these variations. When scaled to the work output, variations of PCr consumption account for 65% of pH changes through a linear relationship. This linear relationship was substantially improved (90%) when both variables were scaled to the square of work output performed (P1 and P2). By capturing most of the initial interindividual variability (90%), P1 vs. P2 relationship represents an ideal standardization procedure, independent of any anthropometric measurements. This relationship also discloses a significant link between the extent of PCr breakdown and intracellular acidosis regardless of exercise protocol. Moreover, changes in the slope of the P1 vs. P2 regression curve, as measured in old subjects and in selected patients, directly reflect alterations of energy production in muscle.

Background Although Magnetic Resonance Imaging has been widely used as a diagnostic tool in neuromuscular disorders, the analysis of images has remained essentially qualitative. Objectives Even if visual scores of deterioration have been proposed and achieve a good sensitivity their specificity remain low. The calculation and mapping of T2 relaxation time, a quantitative index of fat and muscle physical characteristics, can provide reliable information regarding fatty infiltration and inflammatory signs in neuromuscular disorders. Methods In addition to routine images acquired using T1 and STIR sequences, T2 mapping has been obtained from the dominant thigh of 55 patients with various muscle diseases (myositis, myopathies, rhabdomyolysis) and 36 control subjects. Based on the T2 values, we have developed an automatic segmentation method in order to distinguish muscle from fat. Two variables have been defined i.e . the most frequent T2 values (T2mf) and the numbers of T2 values ranging from 60 ms (the upper limit of normal muscle) to 75 ms (the lower limit of fat) expressed as a surface (NT2 60-75ms). Results We observed large T2 variations in patients and controls with a clear positive effect of age (0.23 p mf and NT2 60–75ms values reduced this variation and were significantly affected by muscle diseases (Table 1). They increased from rabdomyolysis, myositis, to myopathies (Table 2). A diagnostic strategy obtained from a CHAID analysis shows that if STIR images analyses were not convincing to conclude, T2 mf and NT2 60–75ms variable allowed to distinguish patients from controls. Conclusions T2 mapping is a quantitative approach more robust than the sole visual inspection to characterize changes in the muscles of patients with neuromuscular diseases. Additional indices such as T2 mf and NT2 60–75ms provide alternative measures of disease activity which could be used for diagnosis, investigation of the natural history of muscle diseases and the effects of therapeutic strategies. Disclosure of Interest None declared DOI 10.1136/annrheumdis-2014-eular.1602

Introduction L’insulino-resistance, l’accumulation d’acides gras et l’alteration de la fonction mitochondriale dans le muscle squelettique pourraient jouer un role majeur dans le developpement du diabete de type 2 (DT2). Cette etude vise a mieux comprendre les relations de causalite entre ces evenements, un domaine encore sujet a controverse. Materiels et methodes La fonction et le metabolisme energetique du muscle gastrocnemien ont ete etudies chez des rats de type Goto-Kakizaki (GK n = 10) par le biais d’une approche pluridisciplinaire combinant des techniques non invasives d’imagerie (IRM) et de spectroscopie (SRM du phosphore 31) par resonance magnetique et des mesures complementaires in vitro. Le rat GK, un modele du DT2, developpe une insulino-resistance peripherique en l’absence d’un taux eleve d’acides gras. Des rats Wistar (n = 10) ont ete utilises comme controles. Resultats Le metabolisme energetique basal est perturbe chez les rats GK avec notamment des reserves plus faibles en phosphocreatine (24 ± 1 vs 32 ± 2 μmol/g), ainsi qu’un pH intracellulaire plus eleve (7,14 ± 0,03 vs 7,06 ± 0,01). Au cours d’un exercice musculaire standardise induit in vivo par electrostimulation transcutanee (6 min de contractions isometriques maximale repetees a une frequence de 1,7 Hz), la performance musculaire est diminuee de 22 % chez les animaux diabetiques bien que l’efficacite energetique de la contraction ne differe pas du groupe controle. En outre, la capacite maximale de production d’ATP par les phosphorylations oxydatives mitochondriales, ainsi que l’activite de la citrate synthase ne sont pas alterees chez le GK. Conclusion L’absence de dysfonctionnement mitochondrial suggere que cet evenement n’est pas la cause du developpement de l’insulino-resistance dans ce modele diabetique et renforce l’hypothese que la fonction mitochondriale et le metabolisme des acides gras sont etroitement lies dans l’etiologie du diabete de type 2.

1. In ischaemic exercise ATP is supplied only by glycogenolysis and net splitting of phosphocreatine (PCr). Furthermore, 'proton balance' involves only glycolytic lactate/H+ generation and net H+ 'consumption' by PCr splitting. This work examines the interplay between these, metabolic regulation and the creatine kinase equilibrium. 2. Nine male subjects (age 25-45 years) performed finger flexion (7 % maximal voluntary contraction at 0.67 Hz) under cuff ischaemia. 31P magnetic resonance spectra were acquired from finger flexor muscle in a 4.7 T magnet using a 5 cm surface coil. 3. Initial PCr depletion rate estimates total ATP turnover rate; glycolytic ATP synthesis was obtained from this and changes in [PCr], and then used to obtain flux through 'distal' glycolysis (phosphofructokinase and beyond) to lactate; 'proximal' flux (through phosphorylase) was obtained from this and changes in [phosphomonoester]. Total H+ load (lactate load less H+ consumption) was used to estimate cytosolic buffer capacity (beta). 4. Glycolytic ATP synthesis increased from near zero while PCr splitting declined. Net H+ load was approximately linear with pH, suggesting beta = 20 mmol x l(-1) (pH unit)(-1) at rest, increasing as pH falls. 5. Relationships between glycolytic rate and changes in [PCr] (i.e. the time-integrated mismatch between ATP use and production), and thus also [P(i)] (substrate for phosphorylase), suggest that increase in glycolysis is due partly to 'open-loop' Ca2+-dependent conversion of phosphorylase b to a, and partly to the 'closed loop' increase in P(i) consequent on net PCr splitting. 6. The 'settings' of these mechanisms have a strong influence on changes in pH and metabolite concentrations.

Background Adverse rheumatological effects of fluoroquinolone treatment such as tendinopathies, arthralgia and myalgia have been reported. The exact mechanism of fluoroquinolone toxicity remains unclear. Objectives To investigate muscle function in patients suffering from severe myalgia resulting from fluoroquinolone treatment. We used histology, in vitro contracture tests (IVCT) and 31P magnetic resonance spectroscopy (31P MRS) to explore muscular contraction and metabolism. Methods Three patients were investigated suffering after fluoroquinolone treatment from myalgia, hyperalgia tendinopathy and arthralgia. Control group included nine subjects, all of them were free of any muscle disease. Muscle biopsies were performed on the left biceps, IVCT were performed in accordance with the protocol recommended by European Malignant Hyperpyrexia Group (EMHG). 31P MRS concicted to MR spectra of forearm flexor muscles were recorded at 4.7 T throughout a rest-exercise-recovery protocol. Results No specific histologic anomalies were observed in muscle biopsies. In vitro contracture tests diagnosed one patient as susceptible to Malignant hyperthermia. 31P MRS detected in all patients a significant reduction of pH magnitude changes measured at end of exercise and a faster rate of proton efflux measured during recovery. Conclusion Muscle abnormalities described in the present study of three patients after fluoroquinolone treatment clearly pointed out the organicity of fluoroquinolone-induced myalgia. All three patients displayed an aceleration of proton efflux and a limited acidosis likely in relation with changes of transporters involving in the transport of Na+, H+ and Ca2+.

Effort-induced hyperthermia, also called exertional heat stroke (EHS) is due to an imbalance between internal heat production and heat loss, generally exacerbated by several factors such as inadequate fluid, caloric, and/or electrolyte intake, and is associated with a classical symptomatology, i.e. increased body temperature (higher than 40°C), neurological impairment that could lead to coma with the addition of rhabdomyolysis-induced myoglobinuria and acute renal failure. EHS generally occurs during strenuous activity under hot and humid environmental conditions. Subjects are often healthy young adults with no apparent clinical or biological deficits. The pathogenesis of a EHS episode differs from a malignant hyperthermia (MH) crisis. However, both conditions share some similarities in symptoms, such as the abnormal increase in core temperature. The triggering agent is different. MH is a disorder of skeletal muscle in which volatile anaesthetics and depolarizing muscle relaxants trigger a sustained increase in myoplasmic calcium concentration, thereby producing hyper-metabolic and contractile activities. MH crisis occurs in predisposed subjects and leads to a dramatic increase in core temperature. In addition, neurological signs are rarely recorded during a MH crisis, and dantrolene is used to prevent a fatal issue, whereas cooling is largely used as therapy during EHS. DNA mutations involved in the susceptibility to MH have been reported for only 50% of subjects susceptible to MH and for the remaining 50% this information is still not available. With respect to EHS subjects, no information regarding MH mutations has been reported so far. Due to some similarities between MH and EHS, it could be hypothesised that EHS, in the same way as MH, is associated with the existence of an infraclinical myopathy. In this respect, electromyographic, histological and metabolic studies have provided conflicting and scanty results. In the present study, we analysed the physiological (using in vitro contracture tests) and metabolic (using 31-phosphorus magnetic resonance spectroscopy, 31P MRS) bases of EHS. We addressed the issue of possible etiological similarity between the group of EHS subjects and MH susceptible (MHS) subjects for whom a noninvasive diagnostic strategy has been recently reported. Using 31P magnetic resonance spectroscopy, we have analysed the muscle energetics of 26 EHS subjects for whom in vitro halothane-caffeine contracture tests were abnormal and investigated possible similarities with subjects susceptible to malignant hyperthermia. An early decrease of pH was noted during the first minute of exercise in EHS subjects as compared to controls. EHS subjects were divided into two subgroups according to the diagnostic score previously developed for MHS subjects. The 19 subjects (73%) with a score higher than 2 displayed a significantly larger caffeine-induced and earlier ryanodine-induced contractures on muscle biopsies as compared to the rest of the group (7 subjects). The results demonstrate that muscle energetics is abnormal in subjects who have suffered from EHS and suggest a possible link between MH and EH, although all EHS patients cannot be considered as MHS. Metabolic abnormalities in EHS subjects detected by 31P MRS may indicate a defect affecting the calcium release channel of the sarcoplasmic reticulum which translates as a very abnormal ryanodine contracture test by IVCT. We conclude that, similarly to MH crisis, EHS is related to a failure of muscle energetics that may be associated with a latent myopathy which is readily identified by non invasive 31P MR spectroscopy.

Exertional heat stroke (EHS) is usually triggered by strenuous exercise performed under hot and humid environmental conditions. Although the pathogenesis of an EHS episode differs from that of a clinical malignant hyperthermia (MH) crisis, both conditions share some similarities in symptoms, such as the abnormal increase in core temperature. By use of (31)P magnetic resonance spectroscopy, we analyzed the muscle energetics of 26 post-EHS subjects for whom in vitro halothane/caffeine contracture tests were abnormal and investigated possible similarities with subjects susceptible to MH. An early decrease of pH was noted during the first minute of exercise in EHS subjects as compared with controls. EHS subjects were divided into two subgroups according to the diagnostic score previously developed for MH subjects. The 19 subjects (73%) with a score higher than 2 displayed significantly larger caffeine-induced and earlier ryanodine-induced contractures on muscle biopsies as compared with the rest of the group (7 subjects). The results demonstrate that muscle energetics are abnormal in subjects who have experienced EHS and suggest a possible link between MH and EH, although all EHS cannot be considered as MH.

Resume Objectif Comparer la capacite oxydative musculaire des enfants et des adultes a partir de la mesure non invasive de la vitesse de resynthese de la phosphocreatine (PCr) apres un protocole d’effort standardise. Methode Sept garcons et dix hommes ont effectue un exercice de flexion des doigts de trois minutes realise a une frequence de 0,7 Hz contre un poids ajuste a 15 % de la force maximale volontaire. La capacite oxydative mitochondriale a ete mesuree durant la periode de recuperation de 15 minutes a partir de la constante de temps d’une fonction monoexponentielle decrivant la cinetique de recuperation de la phosphocreatine ( k PCr ) et de la vitesse maximale de production oxydative d’ATP ( V max ). Les donnees metaboliques ont ete enregistrees par spectroscopie de RMN du P 31 . Resultats Le pH de fin d’exercice etait identique entre les enfants et les adultes (6,6 ± 0,2 versus 6,5 ± 0,2). k PCr et V max etaient deux fois plus eleves chez les enfants que chez les adultes ( k PCr : 1,7 ± 1,2 versus 0,7 ± 0,2 min −1 ; V max : 49,7 ± 24,6 versus 29,4 ± 7,9 mM min −1 , p Conclusion Les resultats de cette etude illustrent clairement une meilleure capacite oxydative musculaire chez les enfants.

1. Failure of muscle force during sustained fatiguing contraction is associated with myoelectrical and metabolic alterations. However, the inter-relationships between these two types of events remain unclear. The purpose of this study was to examine the effects of decreased oxygen availability during sustained contraction on myoelectrical and metabolic changes, thereby addressing the issue of fatigue. 2. 31P-Magnetic resonance spectra and surface electromyograms were simultaneously recorded in six subjects (three women and three men) performing isometric contraction of forearm flexor muscles sustained at 60% maximum value of force under aerobic or acute hypoxaemic conditions (inhalation of a gas mixture containing 12% O2). 3. The 5 min hypoxaemic rest preceding contraction did not affect the phosphocreatine level and pH value. Under both conditions of oxygen availability, the magnitude of metabolic changes remained similar and the duration of contraction was unaffected (similar workload). However, hypoxaemia significantly reduced the rate of changes in integrated surface electromyogram activity measured in the high-frequency band. Correlative analysis of magnetic resonance spectroscopy and surface electromyogram data shows that for a given surface electromyogram change, metabolic variations were always larger under hypoxaemic conditions. 4. These results suggest that hypoxaemia does not alter metabolic changes, i.e. decrease in pH and phosphocreatine during static contraction. The downward shift of the relationships between myoelectrical and metabolic changes under hypoxaemia points to the existence of a better excitation—contraction coupling in acute hypoxaemia compared with normoxia and this is indicative of an adaptative mechanism.

To analyze metabolic changes associated with a fulminant malignant hyperthermia (MH) crisis developed spontaneously in an MH susceptible pig which was part of 12 pigs undergoing metabolic investigation (six MH susceptible and six controls) and had been anaesthetized with a non-triggering agent (pentobarbitone).The pig was placed in a cradle and then inserted into a 4.7 T magnet bore. The semi-membranous muscle was submitted to three repetitive stimulation-recovery sessions. 31-P magnetic resonance spectra and mechanical data were recorded.The pig developed a non-rigid MH crisis during recovery from the second set of experiments. Although no mechanical work was performed, dramatic metabolic changes were noted. Twitch tension decreased progressively reaching zero while mouth temperature continuously increased to 44.5 degrees C. Phosphocreatine (PCr) consumption was coupled to Pi accumulation. Also, a marked intracellular acidosis and a large accumulation of phosphomonoesters (PME) were observed, probably as a result of massive glycolysis activation. Interestingly, ATP level remained constant.These irreversible mechanisms may constitute a metabolic dead-end coupling calcium pumping ATP-consuming processes and ATP synthesis through PCr breakdown and anaerobic glycolysis. They do not differ from metabolic changes previously reported in rigid forms of MH crisis.

Background Camptocormia also referred to as “bent spine syndrome” is characterized by an abnormal trunk posture with marked flexion of the thoraco-lumbar spine. These clinical signs are most prominent on standing and walking and disappears in the recumbent position. There is definitely a broad spectrum of musculoskeletal and neurological etiologies of this disorder which are likely linked to the referral patter. Camptocormia has been associated with muscular dystrophies, inflammatory myopathies, segmental dystonia, amyotrophic lateral sclerosis, mitochondrial myoapthy, dysferlinopathy and Parkinson disease among others. It has been described as a late-onset (over 50 years-old) myopathy with a progressive weakness of the spinal extensor muscles. Increased CK activity and unspecific EMG changes have been reported while computed tomography and Magnetic resonance imaging (MRI) disclosed fat invasion of paravertebral muscles. However, this fat invasion has never been compared to a proper control group so that the effect of age has been ignored. Objectives The main purpose of the present study was to quantify the potential fatty infiltration of paravertebral muscles in patients with primary camptocormia and to compare the corresponding results with those from a age-matched control group. Methods Patients (4, 3 women) and age and sex-matched controls (4). Patients group has been investigated 16.4 ± 3 years after the symptoms onset. We used a spin echo T1 weighted MRI sequence in order to record axial slices of paravertabral muscles (TR/TE = 544/12, matrix size 512*512, FoV 20 cm, slice thickness 5 mm) at 1.5 T (Vision plus, Siemens). Subcutaneous fat (SCF), fatty infiltration (FIF) and muscle (MF) fractions were quantified using a threshold procedure previously described (1). Results were expressed as ratio related to the total content including muscle and fat contents. Mann-Whitney tests (p Results The relative intramuscular fat content was actually larger in controls (61±15%) than in patients (38±15%). Correspondingly, the muscle fraction was larger in patients (62 ±19) as compared to controls (39±15%). However, statistical tests failed to demonstrate any difference thereby suggesting that the fatty infiltration of paravertebral muscles previously reported in patients with camptocormia as a myopathic sign should be revisited in the light of ageing. Conclusions This comparative MRI study between patients with camptocormia and age and sex-matched controls clearly indicate similar fatty and water contents in paravertebral muscles. On that basis, one can argue that the fatty infiltration previously reported in patients with camprocormia as a myopathic sign was rather related to ageing. This preliminary study shoud be extended in a larger cohort. References Mattei, J. P., Y. L. Fur, et al. (2006). “Segmentation of fascias, fat and muscle from magnetic resonance images in humans: the DISPIMAG software.” Magma 19(5): 275-9). Disclosure of Interest None Declared

Background Because of its reduced thickness at the carpus level, the MRI identification of cartilage abnormalities has been initially discarded from the usual rheumatologic diagnostic scores and just recently introduced as a qualitative variable related to joint space narrowing. Objectives In the present study we aimed at determining whether carpal cartilage area can be measured using high-field MRI area through a semi-automatic method. We also compared the results related to two different MRI sequences. Methods The study was conducted in 14 healthy volunteers after they provided their written informed consent. MRI investigations were performed at 3T using two 3D sequences i.e. VIBE and DESS for the analysis of carpal cartilage. Cartilage surface was measured on a three-dimensional reconstruction using a conventional image processing radiology software. The protocol received the agreement from the local ethics committee. Results Cartilage measurements performed by two different operators and twice by the same operator showed a very good reproducibility regardless the MRI sequence used. A 15% interindividual variability for the cartilage area was quantified within this control group. Interestingly, the wrist cartilage area was linearly related to the carpal bone height and so for results obtained with both MRI sequences. Conclusions Using high-field MRI, we reported a very reproducible semi-automatic method of cartilage surface measurement in wrist. The measurements were performed on a MRI section accurately defined thanks to 3D acquisitions. The large variability of the corresponding measurements illustrated that cartilage area cannot be used as a stand-alone diagnostic criterion. The standardized linear relationship between wrist cartilage area and carpal bone height captures the natural diversity of these measurements and provides a promising index for future diagnostic and therapeutic studies in the field of rheumatologic diseases. Disclosure of Interest None Declared

Background Primitive progressive lumbar paravertebral muscle weakness commonly known as Primitive Camptocormia and also referred to as “bent spine syndrome” is characterized by an abnormal trunk posture with marked flexion of the thoraco-lumbar spine on standing and walking. It has been described as a late-onset myopathy with a progressive weakness of the spinal extensor muscles associated to a paravertebral muscles fat invasion on the basis of Magnetic resonance imaging (MRI) investigations. In addition, a few case reports have suggested that primitive camptocormia might not be specific of paravertebral muscles but rather a more general myopathy. However, no data of a proper control have been reported so that a age-bias could have been introduced. Objectives The main purpose of the present study was to quantify fat invasion in thigh muscles of patients with primitive camptocormia using MRI in order to determrine whether camptocormia might be considered as a general myopathy. Methods Eight patients (7 females) were recruited and investigated 16.4±3 years after the onset of the first symptoms. Four age, and sex-matched control women were included. Mean patients and controls age were 78.8±7.9 and 81.8±5 year-old, weight was 60.1±2.3 and 61±1.4 kg, height was 159±3and 156±2 cms. The MRI sequence protocol included axial slices of the thigh using T1-weighted spin echo (TR/TE =544/12, matrix size 512*512, FoV 20 cm, slice thickness 5 mm) at 1.5 T (Vision plus, Siemens). A semi-automatic home-developed tool was used in order to quantify on each slice the muscle, subcutaneous fat (SCC) and infiltrated fat (IF) compartments (1). Results were expressed as means ratios with respect to the total (fat + muscle) fraction. Mann-Whitney tests (p Results As summarized in table 1, muscle was the larger compartment in both groups with a similar fatty infiltration. Conclusions On the basis of quantitative MRI measurements, the present results clearly showed that fatty infiltration of thigh muscles, a potential myopathic index, was not larger in patients suffering from a primitive progressive lumbar paravertebral muscle weakness. We also quantified a 20-25% fat infiltration in older subjects. Our results did not confirm those from previous studies suggesting an abnormal muscle fat invasion in primitive camptocormia. However, given that no proper control group was included, the conclusions might have been biased. Muscle fat invasion would then be specific to paravertebral muscles in patients with camptocormia and could not be considered as an index of a general myopathic process. References Mattei, J.P., Y.L. Fur, et al. (2006). Segmentation of fascias, fat and muscle from magnetic resonance images in humans: the DISPIMAG software. Magma 19(5): 275-9). Disclosure of Interest None Declared

Nemaline myopathy (NM) is the most common disease entity among non-dystrophic skeletal muscle congenital diseases. Mutations in the skeletal muscle α-actin gene (ACTA1) account for ∼25% of all NM cases and are the most frequent cause of severe forms of NM. So far, the mechanisms underlying muscle weakness in NM patients remain unclear. Additionally, recent Magnetic Resonance Imaging (MRI) studies reported a progressive fatty infiltration of skeletal muscle with a specific muscle involvement in patients with ACTA1 mutations. We investigated strictly noninvasively the gastrocnemius muscle function of a mouse model carrying a mutation in the ACTA1 gene (H40Y). Skeletal muscle anatomy (hindlimb muscles and fat volumes) and energy metabolism were studied using MRI and (31)Phosphorus magnetic resonance spectroscopy. Skeletal muscle contractile performance was investigated while applying a force-frequency protocol (from 1-150 Hz) and a fatigue protocol (80 stimuli at 40 Hz). H40Y mice showed a reduction of both absolute (-40%) and specific (-25%) maximal force production as compared to controls. Interestingly, muscle weakness was associated with an improved resistance to fatigue (+40%) and an increased energy cost. On the contrary, the force frequency relationship was not modified in H40Y mice and the extent of fatty infiltration was minor and not different from the WT group. We concluded that the H40Y mouse model does not reproduce human MRI findings but shows a severe muscle weakness which might be related to an alteration of intrinsic muscular properties. The increased energy cost in H40Y mice might be related to either an impaired mitochondrial function or an alteration at the cross-bridges level. Overall, we provided a unique set of anatomic, metabolic and functional biomarkers that might be relevant for monitoring the progression of NM disease but also for assessing the efficacy of potential therapeutic interventions at a preclinical level.

Publisher Summary 31P magnetic resonance spectroscopy (MRS) has become a tool of choice to investigate noninvasively the energetic metabolism of human muscle. As the first applications to animal models, MRS technology has evolved with the development of rf surface coils and the availability of high field wide-bore superconducting magnets. Metabolic explorations have then been extended to in situ situations in animals and humans. This chapter focuses on the exploration of human muscle energetics by MRS. It also presents the specific information learned from MRS on the diagnosis of various forms of myopathies and the follow-up therapies. The chapter describes applications to malignant hyperthermia and discusses why the current results highlight the need of a standardized protocol for these metabolic explorations and reinforce the central role of MRS within a multidisciplinary network involved in the investigation of muscle metabolic disorders.

P NMR spectroscopy. While initial rates of [PCr] consumptionand [PCr] resynthesis were not modified, relative [PCr] consumption and energy consumption per specific workload were significantly larger in mstn-/- mice compared to WT mice. Differently to our previous report, here we show that maximal tetanic tension increase dproportionally with muscle size. However, mstn-/- muscles fatigued as rapidly that no force advantage remained over WT muscles following 3 min of repetitive stimulation. Similar results were obtained following myostatin blockade in adult mice.

BACKGROUND Histological anomalies associated with malignant hyperthermia (MH) have been scarcely reported. In some patients susceptible to MH (MHS), central cores have been identified and a genetic association has been proposed, but multiminicore lesions have not been systematically reported. OBJECTIVE To analyze the association between multiminicores and MHS in a large family with MH with an approach combining histology, in vitro contracture tests, and genetic analysis. PATIENTS AND METHODS Twenty-nine members of an MH family (147 members) were investigated. MAIN OUTCOME MEASURES Muscle biopsy specimens were analyzed histologically and with in vitro contracture tests. Genetic analyses were performed to determine the presence of mutations in the ryanodine receptor (RYR1) gene. RESULTS According to the gold standard in vitro contracture tests, 17 patients were diagnosed as having MHS and 10 as not being susceptible. Multiminicores were found in 16 of the 17 MHS patients and in a single nonsusceptible participant. A linkage between the MH trait and the RYR1 locus in chromosome 19 was demonstrated, whereas no already known mutations were found. Two missense heterozygous mutations (R2676W and T2787S) were identified from sequencing of the entire coding complementary DNA. Overall, we found a significant association between MHS and the presence of multiminicores (chi(2) = 26.5, P

Two patients with mitochondrial encephalomyopathy due to complexes I and IV deficiencies received 150 mg/d of coenzyme Q 10 (CoQ). We studied them with a bicycle ergometer exercise test and 31 P NMR spectroscopy before and after 10 months of treatment. Before treatment, we observed a low phosphocreatine/inorganic phosphate (PCr/P i ) resting value along with abnormally high resting lactate concentration. During exercise, there was a pronounced acidosis with delayed kinetics of postexercise recovery for blood lactate, pH, PCr, and PCr/P i ratio. Oxygen uptake during exercise was reduced while the lowering of the ventilatory threshold indicated an early activation of glycolysis. After treatment, the bicycle ergometer exercise test indicated a significant improvement with a decrease in resting blood lactate level, an increase in oxygen consumption during exercise, and an increase in the kinetics of lactate disappearance during the recovery period. A shift of the ventilatory threshold to higher workload was present. 31 P NMR spectroscopy confirmed the improvement, showing a significant increase in the PCr/P i ratio at rest and in the kinetics of recovery for pH, PCr, and PCr/P i ratio following exercise in patient 1. For patient 2, we observed a less pronounced acidosis correlated with a lesser amount of P i produced during exercise. These observations indicate an improvement of mitochondrial function and a shift from high to low glycolytic activity in both patients consequent to CoQ treatment.

31P NMR spectroscopy at 4.7 T has been used to follow changes in phosphorylated metabolites and pHi in the flexor digitorum superficialis muscle of 15 healthy volunteers subjected to a rest-exercise-recovery protocol. Phosphomonoesters (Pme) increased during exercise and exhibited a delayed recovery to resting level. During early recovery, Pi fell below resting concentration without correlated PCr oversynthesis while Pme level stayed above its resting value. The sum Pi + Pme remained constant. These observations suggest that Pi could be trapped into the glycogenolytic pathway during exercise leading to Pme production. This trapping and the slow Pme recovery could account for transient Pi disappearance observed during recovery.

The relationship of inorganic phosphate (P(i)) and its diprotonated form (H(2)PO(4)(-)) to isometric force (F) was analyzed non-invasively using 31P-magnetic resonance spectroscopy. Rat gastrocnemius muscles were electrically stimulated at six different frequencies in order to produce different levels of fatigue. A curvilinear relationship was demonstrated between force production and [P(i)] and [H(2)PO(4)(-)] accumulation. [P(i)] and [H(2)PO(4)(-)] were correlated with F at the end of the stimulation period but not when F was maximal at the early stage of the stimulation period. Interestingly, the respective [P(i)] and [H(2)PO(4)(-)] did not differ significantly between these two stages demonstrating that [P(i)] and [H(2)PO(4)(-)] cannot be considered as direct effectors of fatigue. This time-dependent and indirect effect of [P(i)] and [H(2)PO(4)(-)] on force production might be mediated by calcium ions.

31P NMR spectroscopy at 4.7 T has been used in vivo to follow metabolic changes associated with exercise and subsequent recovery in the forearm flexor digitorum superficial muscle of 14 healthy volunteers. The muscle content in phosphomonoesters at rest provides an index of glycogenolytic activity. Quantitative linear correlations have been shown to link end-of-exercise acidosis to recovery kinetics of phosphocreatine and phosphocreatine/organic phosphate ratio. These linear relationships constitute new metabolic invariants to be used in the study of myopathies and muscle adaptation to exercise.

The forearm flexor muscles of 56 untrained volunteers (26 women and 30 men) were examined by 31P magnetic resonance spectroscopy, during a rest-exercise-recovery protocol, in order to document the impact of gender on muscle energetics. Absolute concentrations of high-energy phosphate compounds, intracellular pH and rates of aerobic and anaerobic ATP production were calculated. An inverse correlation was found between body mass index (BMI) and power output in women but not in men. After correcting for power output and BMI, the measured energy cost of contraction was twice larger for women than for men. This increase was also reflected in larger ATP production from aerobic and anaerobic pathways. This higher energy cost might be explained in part by differences in local muscle mass, a higher impact of fatness, but also by a reduced metabolic efficiency of muscle fibers in untrained women.

We have analyzed by (31)P MRS the relationship between kinetic parameters of phosphocreatine (PCr) recovery and end-of-exercise status under conditions of moderate and large acidosis induced by dynamic exercise. Thirteen healthy subjects performed muscular contractions at 0.47 Hz (low frequency, moderate exercise) and 0.85 Hz (high frequency, heavy exercise). The rate constant of PCr resynthesis (k(PCr)) varied greatly among subjects (variation coefficients: 43 vs. 57% for LF vs. HF exercises) and protocols (k(PCr) values: 1.3+/-0.5 min(-1) vs. 0.9+/-0.5 min(-1) for LF vs. HF exercises, P

We used31P-magnetic resonance spectroscopy to study proton buffering in finger flexor muscles of eight healthy men (25–45 yr), during brief (18-s) voluntary finger flexion exercise (0.67-Hz contraction at 10% maximum voluntary contraction; 50/50 duty cycle) and 180-s recovery. Phosphocreatine (PCr) concentration fell 19 ± 2% during exercise and then recovered with half time = 0.24 ± 0.01 min. Cell pH rose by 0.058 ± 0.003 units during exercise as a result of H+consumption by PCr splitting, which (assuming no lactate production or H+efflux) implies a plausible non-Pibuffer capacity of 20 ± 3 mmol · l intracellular water−1· pH unit−1. There was thus no evidence of significant glycogenolysis to lactate during exercise. Analysis of PCr kinetics as a classic linear response suggests that oxidative ATP synthesis reached 48 ± 2% of ATP demand by the end of exercise; the rest was met by PCr splitting. Postexercise pH recovery was faster than predicted, suggesting “excess proton” production, with a peak value of 0.6 ± 0.2 mmol/l intracellular water at 0.45 min of recovery, which might be due to, e.g., proton influx driven by cellular alkalinization, or a small glycolytic contribution to PCr resynthesis in recovery.

BackgroundInformations about the effects of exercice training on diabetesinduced myocardial dysfunctions are lacking. Consequently, we investigated the effect of exercice training on the sensitivity of the type 2 diabetic Goto-Kakizaki (GK) rat heart to ischaemia-reperfusion injury by using a multiparametric approach combining 31P magnetic resonance spectroscopy (MRS) with simultaneous measurement of contractile function and biochemical assays.Materials and Methods8-month-old male GK rat (n=11, trained GK) rats ran 60 min on a treadmill 5 days/week at a speed of 20 m/min for 7 weeks and compared with age-matched male Control (n=6) and untrained GK (n=11) rats. Then, isolated rat hearts were perfused with a physiological buffer containing 0.4 mM palmitate, for 24 min before switching to 1.2mM palmitate during 32min low-flow (0.5 ml/min-1.g wet wt-1) ischaemia. Next, flow was restored with 0.4 mM palmitate buffer for 32 minutes. High energy compounds and intracellular pH were followed using 31P MRS with simultaneous measurement of contractile function. Total adenine nucleotides (TAN) and energy charge (EC) were determined in freeze-clamped tissues by H.P.L.C.ResultsHeart to body weight ratios were significantly higher in both untrained and trained diabetic groups (p