Line Hops and Side Hold Rotation Tests Load Both Anterior and Posterior Shoulder: A Biomechanical Study

Area of Science:

• Biomechanics
• Sports Medicine
• Clinical Assessment

Background:

• Clinical tests should accurately simulate the dynamic stresses experienced during athletic activities.
• Understanding the biomechanical and electromyographical demands of clinical tests is essential for selecting appropriate tests for specific sports.

Purpose of the Study:

• To quantify shoulder forces and muscle activation during functional closed-chain tests: Line Hops (LH) and Side Hold Rotation (SHR).

Main Methods:

• A descriptive biomechanical study involving ten asymptomatic participants.
• Utilized 3D video analysis and electromyography to measure shoulder forces, moments, and muscle activity during LH and SHR.
• Assessed muscle activation in terms of % maximum voluntary isometric contraction (MVIC).

Main Results:

• Side Hold Rotation (SHR) generated peak posterior translation forces of 4.84 N/kg and anterior translation forces of 1.57 N/kg.
• Line Hops (LH) produced posterior translational forces of 4.25 N/kg.
• Both tests demonstrated high serratus anterior (98-105% MVIC) and infraspinatus (52-87% MVIC) activation.

Conclusions:

• LH and SHR impose substantial posterior translational forces on shoulder structures, nearing 50% of bodyweight.
• SHR creates significant anterior translation forces (approx. 18% bodyweight) at end-range horizontal abduction.
• LH engages the serratus anterior for propulsion and both serratus anterior and infraspinatus for scapular and humeral stability.