Marker-based motion capture remains the gold standard for baseball pitching motion, but wearable senor technology may also have a role, researchers say.
With the increase in medial ulnar collateral ligament (UCL) injuries in baseball players of all ages and skill levels in recent years, there is a need for a greater understanding of throwing arm mechanics.
The authors of “Are Wearable Sensors Valid and Reliable for Studying the Baseball Pitching Motion? An Independent Comparison With Marker-Based Motion Capture,” wrote, “The motusBASEBALL sensor possesses an inertial measurement unit (IMU) that has been developed and applied to the throwing arm to allow for measurements of several objective parameters, which may prove beneficial for monitoring, rehabilitation, and injury prevention in the throwing athletes. However, the reliability, consistency, and validity of the IMU have not been independently assessed.”
The study was published online in The American Journal of Sports Medicine on August 2, 2021. In it, they compared the reliability, consistency, and validity of the motusBASEBALL sensor compared with that of marker-based motion capture.
Ten healthy male baseball athletes with varsity-level high school experience were included in the study. They wore 37 retroreflective markers for motion capture and the motusBASEBALL inertial measurement unit while throwing 5 fastballs at maximum effort. Arm slot, arm speed, arm stress, and shoulder rotation were all measured by both technologies.
Overall, the inertial measurement unit underreported pitching performance values. Compared with motion capture, it showed significantly different measurements for 3 of the 4 throwing metrics: arm slot (5.0°± 6.1°; p= .037), elbow varus torque (9.4 ± 12.0 N·m; p = .037), and shoulder rotation (6.3°± 6.1°; p = .014).
Reliability was high for shoulder rotation with a less than five degree of error and arm slot has good reliability with less than 10°of error. Arm stress and arm speed, however, weren’t as reliable, the researchers reported.
“The inertial measurement unit was not accurate or valid for arm slot, arm stress, and shoulder rotation compared with marker-based motion capture. It was relatively accurate for arm speed. Despite its lack of validity, it was consistent and reliable for arm speed and shoulder rotation and relatively reliable for arm slot and arm stress. Caution should be used when comparing values provided by this IMU to the gold standard of marker-based motion capture,” they wrote.
“Inertial measurement unit technology has potential to be used in monitoring, rehabilitation, and injury prevention in throwing athletes if valid. This study demonstrates that the values provided by the IMU should not be considered equivalent to those generated by the gold standard of marker-based motion capture; however, there may still be a role for this technology when relying on its internal consistency for intrathrower comparisons and tracking.”
