Reading Data… The Importance of an Accurate Frame of Reference

Sometimes when analyzing video, things are not as they seem visually and can send both athletes and coaches looking down the wrong rabbit hole for solutions. For example, to an observer using the lab frame of reference seen below, the maximum external rotation of the pitcher’s shoulder appears to be no more than 140° from the x-axis.


This has the potential to send many coaches and trainers looking to improve things such as tightness in the lats or prescribing throwing drills to address an inefficient scap load to keep the arm better “connected” to the body in order to try and get more max ER (layback).

Here’s the issue. In this particular situation, this athlete showed NO signs of excessive lat tone / tightness in his table assessment, while his mocap report shows an efficient scap load.

As well as good transfer of energy up the chain as noted by angular velocities (below):

What was even more telling, was that our mocap report tells us that this athlete has 184 degrees of max ER at foot plant!

However, if the angle of the shoulder is measured from the joint (taking into account the severe forward tilt of the spine/trunk), the much more efficient 184° external rotation displayed in this athletes mocap can be seen. By simulating a correction in trunk stack / forward tilt, by rotating a portion of the image the pitcher’s layback becomes much more apparent.

Fig. 2 – Simulation of Corrected Trunk Stack @ FP

These two measurements are on opposite ends of the spectrum of what is considered “efficient” in terms of a pitcher’s maximum shoulder external rotation.

More importantly, it drastically changes what we prescribe in terms of strength / mobility work as well as throwing drills. This athlete would be much better served to prescribe more anterior core work to help to increase his ability to hold spinal torque and stay upright. This would also help improve rotational acceleration and allow him to stay on the ball longer. As for pitching drills, a rocker drill may be well served to allow to feel the COM and help avoid a “front-heavy” landing as well as preventing the arm from “dragging behind” as in Fig. 1 above.

See ya’ in the gym…

Nunzio Signore (Owner RPP Baseball) and Sophie Beier (RPP Bio-mechanist, Master’s Candidate in BioMed at Rutgers University)

RPP Baseball Store

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