To date, no effective treatment is available for Becker muscular dystrophy (BMD) and sporadic inclusion body myositis (sIBM). However, there is a number of promising therapeutic strategies, which are in preclinical development or have moved into clinical trials. Hence, sensitive and specific tools are required for assessment of possible benefit from new treatments. In this regards muscle MRI has been considered a possible alternative outcome measure in these myopathies, although there is no consensus on what muscle MRI protocol should be performed. The purpose of the present monocenter study is to investigate the relation between different muscle MRI sequences and clinical outcome measures in BMD and sIBM patients by direct correlation with clinical and myometric evaluation. We present here baseline findings. The subject images were acquired with a 1.5T Siemens Avanto MRI scanner. The protocol was composed by the following sequences to estimate muscular damage and fat infiltration: 1) a standard axial T1; 2) a volumetric T2-weighted sequence; 3) a 12-echoes spin-echo sequence for the relaxometry analysis; 4) a 2-point Dixon sequence for fat fraction (FF) quantification; 5) a diffusion tensor imaging sequence to study water diffusivity in the muscular tissue. Muscle MRI data were compared with age-matched and sex-matched healthy controls to test validity of our findings. We evaluated 21 patients, aged between 18 and 80 years (mean value 54.1 ± 21.5); 11 patients had sIBM and 10 BMD. Mean baseline muscle FF at thigh level was 44.8 ± 29% in sIBM patients and 39.4 ± 24% in BMD; mean baseline value at leg level was 27.4 ± 26.2% in sIBM and 30.3 ± 22% in BMD. We expect this study will provide a tool for IBM and BMD assessment in clinical practice and in future therapeutic trials.