Advancing Applications of IMUs in Sports Training and Biomechanics.

Miniature inertial measurement units (IMUs) have become popular in the field of biomechanics as an alternative to expensive and cumbersome video-based motion capture (MOCAP). IMUs provide three-axis sensing of angular velocity and linear acceleration in lieu of position data provided by MOCAP. The research presented herein further explores the use of IMUs in five applications for sports training and clinical biomechanics. The first study focuses on the sports of baseball and softball and yields estimates of the release velocity of a pitched ball within 4.6% of MOCAP measurements. The ball angular velocity further distinguishes and quantifies different types of pitches. The second study enables estimates of angular velocity during free-flight based solely on data from an embedded tri-axial accelerometer. Doing so eliminates angular rate gyros, which are often range limited, yet yields angular velocity estimates accurate to within 2%. We further exploit this technique to reveal the rotational stability of rigid bodies in free-flight. The third study extends the use of IMUs to assess the speed of an athlete estimated from a torso-mounted IMU. The speed estimates remain highly correlated with those obtained by MOCAP (r=0.96, slope=0.99) for motions characteristic of explosive sports (e.g., basketball). Moreover, the accurate speed estimation algorithm (mean RMSE=0.35 m/s) does not require data from GPS or magnetometers rendering it valuable and usable in any environment (indoor or outdoor). The remaining studies advance the use of IMU arrays to estimate joint reactions in multibody systems. The fourth study establishes the accuracy of this method using experiments on an instrumented double pendulum. Estimated reaction forces and moments remain within 5.0% and 5.9% RMS respectively of values measured via load cells. The final study addresses the companion need to measure the location of joint centers. A method employing a single IMU yields the center of rotation (CoR) of a spherical joint to within 3 mm as established by a coordinate measuring machine. The simplicity and accuracy of this method may render it attractive for broad use in field, laboratory or clinical applications requiring non-invasive, rapid estimates of joint CoR.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/97947/1/ryanmcg_1.pd