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.
