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Golf is a growing sport supported by a multi-billion dollar industry. Part of this growth can be attributed to new technologies including new training aids. Training aids address one of the major obstacles towards advancement in the sport, namely developing a controlled and consistent swing. Popular camera-based systems for golf swing measurement possess one or more major limitations including 1) extensive set-up and alignment, 2) restriction to indoor use, 3) high cost, 4) lack of portability, 5) placement of instruments (markers) on/near the club head, and 6) time-consuming data processing and analysis. This research resolves these limitations by contributing a highly portable, accurate and inexpensive means to measure golf swing dynamics. Introduced herein is a miniature and wireless six degree-of-freedom MEMS inertial measurement unit that fits entirely within the grip end of the golf club shaft. A companion measurement theory enables the computation of the rigid body dynamics of the golf club from sensor outputs. Flexible body dynamics, if and when needed, are estimated using dynamical models of flexible golf shafts. For putting strokes, the sensor system resolves the three-dimensional position of the club face to within 3 millimeters and the three-dimensional orientation of the club face to within 0.5 degrees, both with millisecond updates. This measurement speed and significant precision enable the detailed characterization of putting strokes. A suite of “putting metrics” is identified that pin-points common putting faults from the measured club head trajectory and orientation. For full swings made with drivers and irons, the system resolves the complete three-dimensional rigid body motion of the club and critical metrics for swing instruction including the swing planes, club head velocity, and the club head orientation throughout the swing. Beyond golf, the measurement theory and hardware design hold significant promise for training systems for numerous other sports. In addition, this technology has relevance to far broader fields of application including, sports injury mechanics, rehabilitation science, gait analysis, surgeon training, etc. This research has contributed the foundation for these upcoming applications, many of which have already been initiated as a bi-product of this study.