Impact of Neuromuscular Control With and Without Electrical Stimulation and Long-term Effect of Kinetic Chain Exercises in Multidirectional Shoulder Instability Patients

The GM300TE COMBO NMES (Gemore Technology Co., Ltd., New Taipei City, Taiwan), a portable machine with dual controllable channels and a manual switch, will be applied to the biceps long head, infraspinatus, middle deltoid, LT and SA. Muscle force generation is modulated by stimulated frequency, pulse width, and intensity [Bdaiwi et al., 2015]. It linearly increases with stimulated amplitude and pulse duration. The electronics of the unit creates the electrical impulses with an output frequency of 50 Hz and a pulse width of 300 microseconds. The synchronous (S) mode and asymmetrical rectangular wave-pulse will be used throughout the experiment following protocol from previous research (Bdaiwi, et al., 2015). The amplitude will be settled as muscle motor-level contraction with self-perception of maximal tolerable intensity. The time of tetanic stimulation is 7 seconds with 20-second intervals between stimulations to avoid muscle fatigue. The two circular electrodes are used on each muscl

To ensure that the humeral head remains centered during the three specific isometric tasks, the examiner positioned the shoulder according to the direction of instability (anterior, inferior, or posterior) by placing the arm in 20° of shoulder flexion, 0° (neutral), or 10° of extension, respectively. In each position, the examiner gently applied a downward force on the upper arm in a horizontal direction, and the participant was instructed to gently resist the force. The goal was to guide the humeral head gradually toward the center of the glenoid, without excessive scapular movement. This training was directly supervised by a physical therapist, who provided verbal and tactile feedback to ensure correct movement execution (Figure 1). The physical therapist was also responsible for conducting the USG assessment. After a 5-minute familiarization session, participants performed the designated instability-specific isometric task for 3 repetitions.