EIM is a non-invasive, painless, and fast technique for obtaining information on how a patient's muscle structure is changing. EIM uses a small electrical current to measure the health of the underlying muscle. The patient will be asked to lie down and a trained clinical evaluator will perform testing on 16 total muscles (8 on each side) on your arms and legs.

Subjects are seated in front of a 3D camera and asked to perform a standardized upper extremity movement protocol under the supervision of a study clinical evaluator.

Strength testing will be performed using manual muscle testing (MMT) using a hand held force dynamometer.

The researchers will obtain bedside spirometry including forced vital capacity and forced expiratory volume in 1 second.

The researchers will obtain maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) using bedside spirometry.

Whole body and regional lean muscle mass (LMM) will be measured via Dual Energy X-Ray Absorptiometry (DEXA).

A limited physical exam and strength testing will be used to derive two FSHD clinical severity scores. These severity scores both rank weakness in the face, shoulders, arms, distal, and proximal lower extremities on either a 10 or 15 point scale.

The HI is a 15 domain questionnaire designed and based on patient interviews to measure total FSHD health-related quality-of-life, including both motor impairment and the social and emotional impact of FSHD. 116 questions are combined into a total score, the score is transformed onto a percentage scale, with 100 representing maximal disability, and lower scores representing decreasing disability.

The PROMIS57 is an instrument developed by the NIH which generates scores for physical function, and the impact of physical limitations on daily life. 57 questions are summed into a total score, which is transformed into a normalized t-score with 50 representing normal, and lower scores representing increasing disability.

This index measures upper extremity dysfunction. 20 questions are combined into a total score, the score is transformed into a normalized score with 80 representing normal, and lower scores representing increasing disability.

The FDI is a short 5 item questionnaire. The five questions are summed into total score which transformed onto a percentage scale, with 100 representing normal, and lower scores representing increasing disability.

Fall assessment will be completed weekly for 3 months after the month 3 visit.

Participants will be asked to complete a self-assessment "domain-delta" questionnaire at 3, 12, 18 and 24-month visits. The purpose of the "domain-delta" questionnaire is to determine each patient's perceived change in their health-related quality-of-life in the last 6-months. This questionnaire will inquire about total health as well as health related to 14 subdomains self-identified as important by patients during development of the FSHD Health Index. Participants indicate their perceived change by answering if an area "is a lot worse", "is a little worse", "there has been no change", "it is a little better", or "it is a lot better" for each subdomain.

Force will be measured on digital myometer, in KG-force.

Will be performed on 30 subjects at European and United Kingdom sites only. Participants will undergo one needle muscle biopsy of one lower extremity muscle (Vastus Lateralis (VL), Tibialis Anterior (TA), Medial Gastrocnemius (MG), or Lateral Gastrocnemius (LG)) at any study visit. For each biopsy, approximately three muscle tissue samples will be collected, two samples will be individually flash frozen in liquid nitrogen while the third sample will be put into media for myoblast cell cultures.

DNA and RNA will be collected at Baseline and 3-month visits. Plasma and serum samples will be collected at every visit (Baseline, 3, 12, 18, and 24-months).