A non-ischemic forearm exercise test for the screening of patients with exercise intolerance

Background: The forearm exercise test is a common investigation that allows detection of some metabolic myopathies. It is not completely standardized and, when performed in ischemic conditions, may induce rhabdomyolysis in pa tients with glycogenosis. Objective: To develop a standardized non-ischemic exercise test for a safe screening of patients with exercise intolerance. Methods: Twenty-six healthy subjects and 32 patients with exercise intolera nce performed an isometric exercise at 70% of the maximal voluntary contrac tion during 30 seconds in non-ischemic conditions. Blood concentrations of creatine kinase, lactate, and ammonia were analyzed. Results: A nearly four fold lactate rise was induced by exercise in healthy subjects. All patients with normal muscle biopsy showed values similar to those of healthy subjec ts. No significant lactate increase was observed in six patients with a myo phosphorylase defect and one with a debrancher defect. Disparate lactate re sponses were observed in 14 patients with a mitochondrial myopathy. The blo od lactate level at rest was abnormally high in four of these patients. The lactate surface normalized by the mechanical energy production was above t he normal range in eight patients. Conclusions: The authors propose a stand ardized non-ischemic grip test that overcomes the main drawbacks of the cla ssic ischemic forearm exercise test. It provides a specific, efficient, and safe screening test for patients with exercise intolerance. Its sensitivit y was very good for patients with a glycogenolysis defect but remains parti al in patients with a mitochondrial disorder.