Effect of Trunk Immobilization on Electromyographic Activity in a Professional Baseball Pitcher: Investigation of Kinetic Chain Catch-Up

Principle Investigator: Jay Smith, M.D.
Project Coordinator: Brian Kotajarvi, PT — kotajarvi.brian@mayo.edu

Figure 1: Professional pitcher winding up for an overhead throw.

The kinetic chain is the term used to describe a 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 was recorded in in 33 muscles using surface and fine wire indwelling electrodes during overhead throws at a target located 60 feet 6 inches away. A professional pitcher completed 10 throws under four different conditions: 1) normal fastball baseball pitch; 2) baseball pitch with trunk immobilization provided by a specially designed TLSO; 3) fastball pitch performed from a standing position without a leg kick; 4) fastball pitch performed from a standing position without a leg kick while wearing a TLSO (Fig. 1). Data has been collected and is in the process of being reduced and analyzed.