This is a developmental protocol to determine the MRI based 31P-MRS changes seen in subjects with mitochondrial myopathy using our dynamic exercise protocol and to identify the ideal variable(s) to represent mitochondrial function.

Inclusion Criteria:

1. Men and women ≥ age 18 years old with primary mitochondrial myopathy
2. Known alteration in electron transport chain activity (<25 % activity of ETC) or known mutations in mitochondrial gene.

Exclusion Criteria:

Failure based on standard clinical MRI Screening form - the form is intended to establish the safety of subjects participating in the MRI scan without divulging any confidentiality information -

Adults with mitochondrial disease