David Bendahan

Segmentation of fascias, fat and muscle from magnetic resonance images in humans: the DISPIMAG software.

Segmentation of human limb MR images into muscle, fat and fascias remains a cumbersome task. We have developed a new software (DISPIMAG) that allows automatic and highly reproducible segmentation of lower-limb MR images. Based on a pixel intensity analysis, this software does not need any previous mathematical or statistical assumptions. It displays a histogram with two main signals corresponding to fat and muscle, and permits an accurate quantification of their relative spatial distribution. To allow a systematic discrimination between muscle and fat in any subject, fixed boundaries were first determined manually in a group of 24 patients. Secondly, an entirely automatic process using these boundaries was tested by three operators on four patients and compared to the manual approach, showing a high concordance.

Capsiate administration results in an uncoupling protein-3 downregulation, an enhanced muscle oxidative capacity and a decreased abdominal fat content in vivo

Objectives:The involvement of skeletal muscle mitochondrial uncoupling protein-3 (UCP3) in the control of energy expenditure in skeletal muscle and at the whole-body level is still a matter of debate. We previously reported that UCP3 downregulation is linked to an enhanced mitochondrial energy metabolism in rat skeletal muscle as a result of acute capsiate treatment. Here, we aimed at investigating noninvasively the effects of chronic capsiate ingestion on metabolic changes occurring in exercising gastrocnemius muscle and at the whole-body level.Methods:We used an original experimental setup allowing a complete noninvasive investigation of gastrocnemius muscle function in situ using 31-phosphorus magnetic resonance spectroscopy. Whole-body fat composition was determined using magnetic resonance imaging and UCP3 gene expression was measured by quantitative real-time RT-PCR analysis.Results:We found that a 14-day daily administration of capsiate (100 mg kg−1 body weight) reduced UCP3 gene expression and increased phosphocreatine level at baseline and during the stimulation period in gastrocnemius muscle. During muscle stimulation, pHi showed a larger alkalosis in the capsiate group suggesting a lower glycolysis and a compensatory higher aerobic contribution to ATP production. Although the capsiate-treated rats were hyperphagic as compared to control animals, they showed a lower weight gain coupled to a decreased abdominal fat content.Conclusion:Overall, our data indicated that capsiate administration contributes to the enhancement of aerobic ATP production and the reduction of body fat content coupled to a UCP3 gene downregulation.

Selective training-induced thigh muscles hypertrophy in professional road cyclists

Muscular adaptations linked to a high volume and intensity of training have been scarcely reported. We aimed at documenting, using MRI, the cross-sectional area changes associated with a high volume and intensity of training in 11 thigh muscles of a population of professional road cyclists as compared with sport science students. We were also interested in determining, whether selective muscle hypertrophy in professional road cyclists, if any, was correlated to selective exercise-induced T2 changes during a pedaling exercise on a cycloergometer. Cross-sectional area of 11 thigh muscles was quantified in sixteen subjects (i.e. eight professional road cyclists and eight sport science students) using MRI. In addition, transverse relaxation times (T2) were measured before and just after a maximal standardized constant-load exercise in order to investigate exercise-related T2 changes in these muscles. Professional road cyclists had a significantly higher relative amount of muscle (including the whole set of thigh muscles, 90.5±3.3%) as compared to controls (81.6±7.3%). Regarding relative values expressed with respect to the total thigh muscles CSA, Vastus lateralis and Biceps femoris CSA were significantly larger in cyclists whereas CSA of the Vastus intermedius was smaller. However, this selective hypertrophy was not correlated to the exercise-induced T2-increase. We have reported, for the first time, a selective hypertrophy of Vastus lateralis and Biceps femoris in professional road cyclists confirming their involvement in pedaling task and suggesting a possible cause–effect relationship between muscle activation and hypertrophy, associated with a specific pedaling skill.

23 – 31P NMR Spectroscopy of Metabolic Changes Associated with Muscle Exercise: Physiopathological Applications

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.