In the field of neuromuscular disorders (NMD), fat fraction (FF) is an established biomarker of disease severity and water T1 (T1H2O) has been shown to be a potential biomarker of disease activity. Those can be efficiently estimated through Magnetic Resonance Fingerprinting. However for muscle studies water-fat separation and FF quantification increase drastically the size of the dictionary and pattern matching time. We introduce here a bicomponent dictionary where water and fat signals are stored separately. This approach allows improving MRF performance and increasing the accuracy of FF quantification.