摘要：Background: The lower extremity muscle strength has been shown to be weaker in patients with diabetes mellitus, primarily due to the effects of diabetic polyneuropathy, a common diabetic complication. With respect to assessments of the lower extremity muscle strength, reference values for the knee extension force in healthy Japanese subjects have been reported. The clinical significance of applying knee extension force in the assessment of efficacy of exercise therapy and patient education has also been demonstrated, and the use of an individualized approach in physical exercise based on the quantitative assessment of the lower extremity muscle strength is becoming one of the most important strategies for promoting effective rehabilitation. Methods: The study is a multicenter, cross-sectional investigation. We will measure the knee extension force and evaluate the diabetic polyneuropathy in patients with type 2 diabetes using uniform equipment and methodology at all centers. We will compare the knee extension force between the subjects with and without diabetic polyneuropathy and will investigate the associations between the knee extension force and both glycemic control and exercise habits. The trial registration is UMIN CTR (UMIN000002810). Discussion: The lower extremity muscle strength has been insufficiently investigated in Japanese patients with diabetes. This study was designed to establish reference values for the knee extension force in Japanese diabetic patients with and without diabetic polyneuropathy.