Specific changes in water diffusivity due to passive shortening and lengthening of the thigh muscles – A Diffusion Tensor Imaging study

Introduction The organization of skeletal muscle fibers, or muscle architecture, strongly determines the muscle’s maximum force capacity [1]. Diffusion tensor imaging (DTI), widely used in brain studies, has recently emerged as an attractive tool for investigating the microstructure of skeletal muscle. In this latter, DTI provides information about the water molecules self-diffusion which is restricted by physical barriers such as membranes, cytoskeleton and cellular organelles i.e. mitochondria and sarcoplasmic reticulum [2]. Considering skeletal muscle as a network of parallel and elongated fibers, longitudinal water diffusion is facilitated as compared to diffusion in radial directions. Recent studies performed in the human calf muscle [3, 4] have investigated the effects of passive muscle length changes on diffusion properties and shown an increase in mean diffusivity with muscle shortening. So far, this muscle length (or joint angle) dependence of diffusivity has however never been investigated in human thigh muscles, for which only few DTI studies [5, 6] have been carried out. The investigation of thigh muscles organization is of interest given that their architecture might be largely affected in neuromuscular disorders [7]. The present study investigated whether the DTI metrics were sensitive enough to structural muscle fiber changes induced by both passive shortening and lengthening of the thigh muscles.