The purpose of this work was to study the impact of fat model on the quantification of fatty infiltration in skeletal muscle. To this end, we acquired multi-echo 1H-NMRS from 23 subjects affected by an inflammatory myopathy and measured the lipid spectrum of each subject. We also acquired 3D gradient echo volumes at different TEs. Fat and water maps were reconstructed in two cases: (i) with a unique mean fat model (ii) with a fat model specific to each subject. The results of comparison showed a good agreement between both methods and the difference never exceeded 4%.