Reflex muscle contraction in anterior shoulder instability

Scapular Muscle Recruitment Pattern: Electromyographic Response of the Trapezius Muscle to Sudden Shoulder Movement Before and After a Fatiguing Exercise

“…However, research on recruitment patterns and timing of muscle activity in the shoulder is limited. 2,8,61 Wadsworth and Bullock-Saxton 60 examined the temporal recruitment patterns of the scapular rotator muscles during controlled voluntary abduction in the scapular plane. Their results indicated that in noninjured shoulders, the upper trapezius was activated prior to the movement, whereas the lower trapezius was not recruited until after the start of the shoulder movement.…”

Scapulothoracic latent muscle reaction timing comparison between trained overhead throwers and untrained control subjects

“…In studying 12 patients who had unilateral glenohumeral joint instability, Wallace et al (1997) did not observe significant infraspinatus and pectoralis major (sternal head) LMRT differences compared with the contralateral non‐impaired glenohumeral joint in response to sudden anterior translation perturbations. The anterior glenohumeral joint translational perturbation force used in their study however likely necessitated considerably stronger neuromuscular responses to prevent joint injury than the rotational perturbation used in our study, thereby making comparatively more subtle neuromuscular activation timing differences difficult to appreciate (Wallace et al, 1997). The perturbation velocity (approximately 200°/s) and range of motion (45° maximum) used in our study was applied in a rotational manner that simulated overhead throwing, but which also minimized shoulder injury risk, and did not require neuromuscular activation for dynamic joint stabilization purposes.…”

“…Shoulder proprioception studies tend to focus on an individual's ability to sense glenohumeral joint movement or the ability to passively or actively replicate a target position or detect slow velocity positional changes (Smith & Brunelli, 1989;Lephart et al, 1994;Allegrucci et al, 1995;Rogol et al, 1998). To better evaluate the link between peripheral proprioception and ensuing neuromuscular responses several reports have focused on measuring electromyography (EMG) activation following the application of a sudden perturbation or positional change (Clark et al, 1985;Taylor & McCloskey, 1990;Wallace et al, 1997;Brindle et al, 1999;Myers et al, 2003). Although it does not directly measure proprioception, latent muscle reaction timing (LMRT) measurements can be used to identify sensorimotor responsiveness.…”

Kinematic and EMG characteristics of simple shoulder movements with proprioception and visual feedback

“…1(a)). The movable arm represented the forearm position relative to the stationary arm and provided a measure of upper extremity kinematics as an estimate of glenohumeral motion [1,28,39,34,4,42]. A retractable third buttress was used to consistently position the movable arm of the shoulder wheel 27°from the starting position, indicating the target position.…”