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06
15
2011

The Limitations of Two-Dimensional Kinematic Analysis

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A clip on YouTube that has gotten a fair amount of press is this SOMAX Sports clip of Tim Lincecum. There are a lot of assumptions that are made in this video with regard to training and flexibility that I’m not going to get into at this time, but I would like to address this very obviously wrong portion of the video.

Tim Lincecum at MER

Tim Lincecum at MER

The measurement on the still frame to the left is not mine, it is what SOMAX believes Lincecum’s maximum external rotation is – taken straight from their YouTube video analysis.

This is very incorrect and is immediately obvious to anyone who has taken a high school physics course. Attempting to measure the degree of an angle when your line of sight is not directly perpendicular to the angle being measured is a serious error in physics called parallax error. SOMAX makes this very elementary mistake when attempting to analyze Tim Lincecum’s motion.

If you were to adjust the camera to be perpendicular to Lincecum’s acromial line, you would quite obviously get a reading near 90 degrees (MER is usually measured with the shoulder internally rotated at 90 degrees per ASMI’s standards, so this would really be 180 degrees) and not 65 degrees like SOMAX believes.

This is yet another reason why two-dimensional kinematic analyses are spotty when not properly controlled for (as in most game situations), and why serious analysis should rely on multiple high-speed cameras used to reconstruct a three-dimensional model of a pitcher.

I wouldn’t trust any “sports performance institute” that relied on video-based coaching tools if they couldn’t properly adjust for a simple error that a 9th grade physics student could probably pick out, but that’s just me.

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