In Vivo Biomechanics of Human Shoulder
Principal Investigator: Jay Smith, M.D.
Project Coordinator: Denny Padgett, PT — padgett.denny@mayo.edu
Effect of Trunk Immobilization on Shoulder EMG Activity During Throwing
The kinetic chain is the term used to describe the series of linked body segments activated in a coordinated fashion to generate, transfer, and dissipate energy for the purposes of functional motion. During throwing, the majority of kinetic energy is generated proximal to the shoulder girdle, leaving the shoulder susceptible to injury if a proximal kinetic chain breakdown occurs. Over time, kinetic chain catch-up at the shoulder level can lead to sub-optimal performance and injury.
In this study the specific aims are: (1) To quantify the changes in EMG activity of selected shoulder girdle muscles after trunk immobilization, (2) To document the electrophysiologic effects of core dysfunction (i.e. tri-planar trunk motion restriction) on the shoulder girdle and provide a scientific rationale for prescription of core stabilization exercises in the overhead athlete, (3) To provide in vivo quantitative support for the theory of kinetic chain "catch-up". To accomplish these aims EMG activity will be recorded in shoulder girdle muscles of 10 normal subjects during overhead throwing of a baseball (Figure 12).
Figure 12: Throwing with custom TLSO
Electromyographic Activity in the Immobilized Shoulder Girdle Musculature
Post-injury or post-operative shoulder sling immobilization likely has detrimental effects on shoulder muscle function. Maintaining low levels of muscular activity while adhering to motion restriction guidelines may minimize the adverse effects of immobility and facilitate shoulder rehabilitation. Relatively low levels (<20% maximal voluntary contraction (MVC)) of shoulder muscle EMG activity have been documented during passive and active assisted motions, and selected closed kinetic chain exercises. Unfortunately, 3-5 weeks of potentially detrimental immobility may precede implementation of these exercises. Prior research in our lab has documented acceptably low (< 20% MVC) EMG activity in the supraspinatus and infraspinatus muscles of the immobilized shoulder during selected contralateral upper limb motions such as the downward reach, cross body reach, and straightforward reach. These initial results have provided a foundation for prescription of contralateral upper limb motions for early shoulder rehabilitation. The current study expands upon this research to clarify ipsilateral shoulder girdle and contralateral upper limb motions that may be useful for early rehabilitation during periods of shoulder girdle immobilization.
