Aims
Facioscapulohumeral muscular dystrophy (FSHD) causes progressive muscle weakness and loss. This study aims to compare changes in quadriceps oxygenation and hemodynamics during maximal voluntary quadriceps isometric contraction (MVCQ) and to determine the relationships between these parameters and systemic oxidative stress markers and muscle structural parameters and muscle volume in patients with FSHD and healthy controls.

Methods and results
17 patients with FSHD and 14 sedentary healthy controls were matched for age and physical activity level. Blood antioxidant status and stress markers were evaluated. The quadriceps tissue oxygenation index was evaluated by near infrared spectroscopy during MVCQ. Quadriceps volume was determined by magnetic resonance imaging. Quadriceps muscle samples were obtained to evaluate muscle fiber typology and mitochondria morphology by transmission electron microcopy (TEM). Groups were compared by the unpaired Student t-test or by the non-parametric Kruskal - Wallis test in case of skewed distributions with p<0.05. Associations were assessed by Spearman correlations. Compared to controls, patients with FSHD displayed a significantly lower local O2 consumption per second that was correlated with significantly lower MVCQ and systemic oxidative stress marker levels. Although no difference in muscle typology was observed between groups, TEM showed abnormal aggregation of mitochondria near blood capillaries in FSHD muscles.

Conclusions
These results suggest that patients with FSHD have a lower O2 demand during MVCQ and that TOI measured by NIRS during MVC could be useful to determine the muscle oxidative capacity. Furthermore, these adaptations are related to the muscle structure reorganization linked to the occurrence of oxidative stress.