Energy Supplements to Improve Exercise Tolerance in Metabolic Myopathies

Inclusion Criteria: * Genetically and/or biochemically verified GSDIIIa. * 18 years or older. Exclusion Criteria: * Clinically significant cardiac or pulmonary disease. * Pregnancy or lactation. * Severe mental disorders or participants that are in other ways unable to understand the purpose of the trials. * Subjects where the investigator assess that it is not possible or very difficult to place an intravenous catheters. * Other conditions of the joints or skeletal muscle such as arthritis or sprains. If the condition is expected to resolve before the study inclusion period is stopped, the subject may be included at a later time. * Moderate to severe muscle weakness, where the participants are not expected to complete 10 minutes of cycle-ergometry exercise at 70 % of VO2peak. * Verified diabetes. * Participation in other clinical trials that may interfere with the results. * Medications that may interfere with the results or increase the risk of bleeding. * Blood-clotting or bleeding disorders. * Blood donation one month or less prior to inclusion.