Development of the Muscle Architecture Based Isokinetic Strength Assessment Position for Shoulder Rotator Muscles

Today, the most commonly used position is the seated position with 45° of shoulder abduction (Abd) in the scapular plane, known as the most functional isokinetic assessment of shoulder-rotator strength (1). However, considering the architectural feature of the rotator muscles, a position where the maximum sarcomere length is obtained, in which the maximum muscle strength is produced, has not been investigated. Ward et al. showed that the shoulder position, in which the sarcomere length of the muscles was between 2.0 - 2.6 µm, was 25⁰ Abd and 20⁰ external rotation (ER) as a result of their study on the rotator cuff muscles architecture (2). The test position selected in isokinetic measurements is the main factor for outcome measurements and the repeatability of the measurements directly depends on the selected position (3). This study was planned to investigate the effects of the position where the shoulder is at 25⁰ Abd and 20⁰ ER to develop the most suitable isokinetic strength evaluation position based on muscle architecture for shoulder rotator muscles.Using IsoMed 2000 device (D. \& R. Ferstl GmbH, Hemau, Germany) we conducted the isokinetic test of concentric (CON) and eccentric (ECC) shoulder internal (IR) and external (ER) strength at the angular velocity of 60˚/s in both Method I (scapular position) and Method II (25⁰ Abd and 20⁰ ER). There were seven days between the testing sessions, and both tests were conducted at the same time of day. The same examiner with experience in performing isokinetic testing with IsoMed 2000 tested all subjects in both testing sessions