The Effectiveness of Overhead Perturbation Training on Joint Position Sense in Patients With Functional Shoulder Instability: A Pilot Study With Blinded, Randomized Controlled Trial Design

Overhead athletic performance requires both static and dynamic mechanisms to coordinate glenohumeral and scapulothoracic stability to induce the appropriate motor response. Active function is predicated on a sufficient balance of muscular strength, endurance, flexibility and neuromuscular response to proprioceptive input. Coordinating, planning and synthesising complex multi-joint information is a process within the central nervous system, from the periphery to the higher centres of the brain, in a synergy of afferent and efferent feedback.

Joint position sense plays an important role for the shoulder joint in two key components of athletic performance: conscious limb placement and unconscious motor patterning in response to external force during movement. Such motor patterns can be characterised as the motor responsiveness to perturbations of joint position. This assists efficiency of muscular coordination when the shoulder is placed in the long lever position during overhead activities, where the desired motor pattern reaction is essential alongside contractile strength for successful performance and attenuation of injury risk. It is suggested that efficiency in neuromuscular control to provide responsive stabilization is necessary to sustain high levels of overhead performance and to avoid injury. The neuromuscular control response of the shoulder musculature on glenohumeral and scapulothoracic joint positions becomes deficient in the presence of structural injury. For example, rotator cuff injury specifically leads to deficiencies in neuromuscular control timing, patterning and strength compared with asymptomatic clients.

Perturbation of upper limb position during overhead activities causes unpredicted change in tissue length, resulting in a responsive pattern of muscular contractions. The OPT exercise series ensures that the deficient client is exposed to positions of vulnerability against displacement of the limb by external force. It is postulated that neural adaptations are induced through introduction of both rhythmic and sudden alterations to these positions A training stimulus (such as OPT) which facilitates neuromuscular control and speed of response to perturbation has potential to enhance overhead function. This signifies the role of neuromuscular control training in both rehabilitation and prevention of shoulder joint injury. The inclusion of this type of exercise training during rehabilitation and as part of injury risk minimisation strategies is an important component to sustain synchronization of muscular movement patterns.

Population in Focus

The subjects recruited for this study will be explained in greater depth further in the proposal, however are characterised by having a degree of functional glenohumeral joint instability. The physiotherapy class setting which will be utilised as the source of referrals is a heterogenous group of upper limb disorder patients, with a distinct sub group of individuals with functional instability who achieve sufficient recovery to meet the criteria for return to sport. According to the Stanmore classification of shoulder instability this group would correspond to Polar type II-III- that is placed on a continuum between atraumatic structural instability and non-structural, muscle patterning instability.