Subjects with clinically or clinico-pathologically defined IBM will be included in this study. Patients with consistent clinical and laboratory features including ages 18 to 80 years, duration of symptoms> 12 months, serum creatine kinases (CK) no greater than 15 times upper limit of normal, prominent weakness of quadriceps and/or finger flexor weakness>shoulder abduction weakness along with some characteristic histopathological findings of endomysial inflammatory infiltrate, rimmed vacuoles and protein accumulation or 15-18 nm filaments will be considered as clinically or clinicopathologically defined IBM as proposed by the European Neuromuscular Center (ENMC IBM working group, 2013).

Subjects with more than 2 of the following criteria, symmetric proximal weakness, elevated CK, electromyography (EMG) suggesting myositis, muscles biopsy showing inflammatory changes, and typical skin rashes of dermatomyositis (DM) will be recruited as dermatomyositis and polymyositis (DM/PM) based on Bohan and Peter criteria.

Healthy controls without any known neuromuscular disorders and no family history of Amyotrophic lateral sclerosis (ALS) will be recruited for the study.

Electrical impedance myography (EIM) is a new electrodiagnostic method of quantitative muscle evaluation. It utilizes concepts of bio impedance, the ability of biological tissue to impede externally applied electrical current.

This scale reflects on muscle strength. It is based on Medical Research Council scale for muscle power, where muscle strength can have a score of 0-5 (0 means no strength and 5 means full strength).Several muscles are examined in Manual Muscle Testing (MMT) and the total strength is reported as the sum of the Medical Research Council (MRC) muscles scale score of each muscles. Total MMT score for this study can range from 0-160, where 0 means no strength in any muscles and 160 means full strength in all the muscles examined.

This scale measure the limitations in daily life from IBM. It ask 10 questions regarding the activities of daily life and each question is scored between 0-4 (Where 4 means no difficulty and 0 means maximum difficulty). Total score can vary from 0-40, and 40 means no limitations in daily life from IBM.

A change in grip strength using a Jamar hand dynamometer to assess the grip strength in every participant. Best of three attempts will be used.

Time will be measured for a participant to stand up from a chair (using arms if necessary), walk 3 meters, turn around, return to the chair, and sit down. The better of two trials will be used.

Distance walked in 6 minutes will be measured. This has been used as a primary and secondary outcome measures in several clinical trials in various neuromuscular disorders.