The Biomechanical Evaluation of Rotator Cuff Muscles Force from the Pronated Grip Pull-Ups

Abstract

This study is aimed to figure out the rotator cuff (RC) muscle activation range when executing the pronated grip pull-up. Thereby, this study provides a specific range that assists to strengthen the RC muscle from the pronated grip pull-up. Initially, a biomechanical model was created to identify the maximum muscle toque occurrence range executing the pullup motion. The surface electromyography (EMG) test was conducted as a data collection using wireless electrodes (Delsys Trigno EMG sensors, ADInstruments) and the 2D video capturing. This study was conducted using the baseball pitchers (n=4; height=1.70±0.02 m; weight=58.75±4.99 kg) who perform maximum ten or possible repetitions of pullup. The data were analyzed from the lab chart reader software 8.1.22 for EMG signal analysis and the human movement analysis software for the video analysis. According to the biomechanical model, the peak muscle toque of whole shoulder muscles occurs in the range of 64◦-180◦ (θp≈126◦) elbow angle (θ) at the ascending and the descending phases. According to the EMG test result, the infraspinatus muscle activation was occurred in the range of 94◦-135◦ in the elbow angle at the eccentric phase. Finally, four variations of the pull-up with detected range and the changes of intensity and volume were used to implement a four weeks period practically. After the implementation, the muscles strength was measured from three different methods using a suspension scaler. There was a minor improvement of strength in RC muscles using this range. Therefore, it is suggested to move 94◦-135◦ angle of elbow to strengthen the RC muscles while performing the pronated grip pull-up.