REDUCING ERRORS IN KINETIC CALCULATIONS - IMPROVED SYNCHRONIZATION OFVIDEO AND GROUND REACTION FORCE RECORDS

A strategy is presented for temporally aligning ground reaction force and kinematic data. Alignment of these data requires marking both the force and video records at a common event. The strategy uses the infor mation content of the video signal, which is A/D converted along with the ground reaction force analog signals, to accomplish this alignment in time. The vertical blanking pulses in the video signal, which defi ne the start of each video field, can be readily identified provided t he correct A/D sampling rate is selected. Knowledge of the position of these vertical blanking pulses relative to the synchronization pulse makes it possible to precisely align the video and analog data in time . Choosing an A/D sampling rate of 598 Hz would enable video and analo g data to be synchronized to within 1/1,196 s. Minimizing temporal ali gnment error results in greater accuracy and reliability in calculatio ns used to determine joint kinetics.