Improving the accuracy of pedometer used by the elderly with the FFT algorithm.

Purpose: The aim of this study was to investigate and improve the accuracy of accelerometer-type pedometers used by the elderly with slow walking speeds, with or without gait disorders, who do or do not use a cane.

Methods: Eighteen subjects walked with a cane (5 males, 13 females; age, 80.9 +/- 7.7 yr; height, 148.1 +/- 7.7 cm; weight, 51.8 +/- 8.8 kg (mean +/- SD); nine had impaired gait), and 31 subjects walked without a cane (7 males, 24 females; age, 80.9 +/- 7.7 yr; height, 148.1 +/- 7.7 cm; weight, 51.8 +/- 8.8 kg; 15 had impaired gait). Subjects walked for approximately 20 m (10 m in each direction and a turning arc) at their own speed. We determined the number of steps by pedometer (PM), by visually counting the actual number of steps (RM), and by the triaxial acceleration signals. The power spectrum of the accelerometer in each direction calculated by fast Fourier transform (FFT) for a 4-s temporal window was normalized with the maximum power of each window. It was composited, and the frequency at maximum power was considered as the cadence. The number of steps taken (FM) was determined by summing all the estimated steps in each window.

Results: PM was significantly less than the RM (P < 0.05), and the error of PM was 53.2 +/- 34.1% of RM. FM did not differ from the RM, and the average error of FM was -0.7 +/- 7.9% of RM (absolute value: 5.8 +/- 5.3%).

Conclusion: We suggest that our FFT method is suitable for estimating the number of steps during walking in this population.