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 information 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 define the start of each video field, can be readily identified, provided the 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 analog data to be synchronized to within 1/1,196 s. Minimizing temporal alignment error results in greater accuracy and .reliability in calculations used to determine joint kinetics.
Brian J. O'Connor, H. John Yack, and Scott C. White
Brian C. Martinson, A. Lauren Crain, Nancy E. Sherwood, Marcia G. Hayes, Nicolaas P. Pronk, and Patrick J. O’Connor
To assess the representativeness of older adults recruited to a physical activity maintenance RCT by conducting sequential comparisons to characterize study sample composition changes occurring between sampling frame construction and study enrollment.
Study subjects (N = 1049) were 50 to 70 year old men and women who had increased physical activity within the past year recruited from a Midwestern managed care organization.
Those responding to an initial mailed screener differed on demographic, behavioral, and SES characteristics from those not responding. Compared with ineligibles, eligible individuals were significantly younger, more highly educated, and more likely to report improved health in the prior year. Compared with eligible individuals who did not enroll, enrollees had generally higher education and income.
Physical activity promotion programs in older adults may have limited reach and substantial volunteer bias. Additional strategies to increase the reach of physical activity interventions into the target population are needed.