Specific muscle strength is reduced in facioscapulohumeral dystrophy: An MRI based musculoskeletal analysis

•Specific muscle strength of the quadriceps muscle is reduced in patients with FSHD.•MRI and muscle modeling can be used to evaluate specific muscle strength in FSHD.•FSHD patients have lower contractile muscle volume and PCSA than healthy controls.•Clinical trials for FSHD should aim for restoration of specific muscle strength. The aim was to test whether strength per unit of muscle area (specific muscle strength) is affected in facioscapulohumeral dystrophy (FSHD) patients, as compared to healthy controls. Ten patients and ten healthy volunteers underwent an MRI examination and maximum voluntary isometric contraction measurements (MVICs) of the quadriceps muscles. Contractile muscle volume, as obtained from the MR images, was combined with the MVICs to calculate the physiological cross-sectional area (PCSA) and muscle strength using a musculoskeletal model. Subsequently, specific strength was calculated for each subject as muscle strength divided by total PCSA. FSHD patients had a reduced quadriceps muscle strength (median(1st quartile–3rd quartile): 2011 (905.4–2775) N vs. 5510 (4727–8321) N, p