High-energy phosphates in the different stages of fatty infiltration and correlation with muscle force.

<p>(<b>A</b>) Representative phosphorous MR spectra of VL muscle of FSHD patients, upper with a normal fat fraction, lower with a high fat fraction. (<b>B</b>) PCr/ATP decreases with fat fraction (mean±SD). In intermediately fat infiltrated muscles the PCr/ATP is already decreased significantly from 4.15±1.00 to 3.57±0.88. Completely fat infiltrated muscles do not show a further decrease of this ratio. (<b>C</b>) Significant correlation between PCr/ATP and muscle strength (p<0.001, R² = 0.29). Pi = inorganic phosphate; PCr = phosphocreatine; ATP = adenosine triphosphate.