Multiple sclerosis (MS) is associated with loss of skeletal muscle mass and function. The myogenic stem cells (satellite cells – SCs) are instrumental to accretion of myonuclei, but remain to be investigated in MS. The present study aimed to compare the SC and myonuclei content between MS patients (n=23) and age matched healthy controls (HC, n=18). Furthermore, the effects of 12 weeks of high intensity training on SC and myonuclei content were explored in MS. Muscle biopsies were obtained from m. Vastus Lateralis at baseline (MS+HC) and following 12 weeks of training (MS only). Frozen biopsies were sectioned followed by immunohistochemical analysis for fiber type specific SCs (Pax7+), myonuclei (MN) and central nuclei content and fiber cross-sectional area (fCSA) using ATPase histochemistry. At baseline the SCs per fiber was lower in type II compared to type I fiber in both MS (119%, p