Muscle Contraction Has a Reduced Effect on Increasing Glenohumeral Stability in the Apprehension Position

Purpose Glenohumeral instability accounts for 23% of all shoulder injuries among collegiate athletes. The apprehension position—combined shoulder abduction and external rotation—commonly reproduces symptoms in athletes with instability. Rehabilitation aims to increase glenohumeral stability by strengthening functional positions. However, it is unclear how much glenohumeral stability increases with muscle contraction in the apprehension position. The purpose of this study was to determine whether the ability to increase translational glenohumeral stiffness, a quantitative measure of glenohumeral stability, with muscle contraction is reduced in the apprehension position. Methods Seventeen asymptomatic adults participated. A precision-instrumented robotic system applied pseudorandom, anterior–posterior displacements to translate the humeral head within the glenoid fossa and measured the resultant forces as participants produced isometric shoulder torques. Measurements were made in neutral abduction (90° abduction/0° external rotation) and apprehension (90° abduction/90° external rotation) positions. Glenohumeral stiffness was estimated from the relationship between applied displacements and resultant forces. The ability to increase glenohumeral stiffness with increasing torque magnitude was compared between positions. Results On average, participants increased glenohumeral stiffness from passive levels by 91% in the neutral abduction position and only...
Source: Medicine and Science in Sports and Exercise - Category: Sports Medicine Tags: APPLIED SCIENCES Source Type: research