The purpose of this study is to develop simple diagnostic screeningtests and investigate potential biomarkers for identifying patients with abnormalities of mitochondrial function, which also can be used as outcome measures in future clinical trials. The study will investigate two submaximal tests: a submaximal handgrip test and a walking test. Furthermore investigators will investigate Acyl-carnitine profiles and GDF-15 levels in patients with mitochondrial myopathy.

Inclusion Criteria:

• age 18-75
• verified mitochondrial myopathy
• or healthy control
• or disease control (another neuromuscular disease)

Exclusion Criteria:

• Patient has any prior or current medical conditions that, in the judgment of the Investigator, would prevent the patient from safely participating in and/or completing all study requirements.
• Patient has symptoms of mitochondrial myopathy due to known secondary mitochondrial dysfunction
• Patient does not have the cognitive capacity to understand/comprehend and complete all study assessments.
• Pregnancy or breastfeeding.

Genetically verified primary Mitochondrial disorder with myopathy.