Investigation of spectral content from discrete plantar areas during adult gait: an expansion of rehabilitation technology

Evaluation of foot contact frequency components with the use of a standard force plate has been reported to be helpful in the clinical assessment of degenerative joint disease. Spectral analysis has also been used as a tool for the evaluation of prosthetic and orthotic designs. In this paper, we examine and employ a new method for determining spectral characteristics of discrete plantar foot surface areas. This method is used to characterize spectral frequency content of foot strike at discrete plantar locations in ten normal controls. Spectral data obtained from a standard force plate are also presented and compared to reports in the literature. Measurements at six discrete points under the foot were made with a custom-manufactured strain gage-based force dosimeter. In addition, measurements of ground reaction forces in the sagittal, coronal, and transverse planes were made using a high resonant frequency force plate during barefoot and shod walks for ten adult male control subjects. Spectral frequency components of all forces measured were determined through Fourier analysis. The hypothesis of the study was that discrete plantar frequencies would be essentially similar to those reported in earlier studies of foot contact with a ground reaction force plate. While Fourier transform of time domain force plate data revealed frequency contents that were contained primarily below 10 Hz, as has been previously reported, higher frequency components associated with impulsive loading at heel strike were also observed (75 Hz for barefoot walk and 60 Hz for shod). The anterior-posterior (AP) frequency spectrum of barefoot walking contained higher amplitude components than did shod walking, though both signals contained dominant frequencies of about 1 Hz. Medial-lateral (ML) frequency analyses were similar for both walking conditions with dominant components of about 4 Hz noted. Broader frequency spectrums were seen in the discrete force dosimeter data. Components were contained mostly below 12 Hz with some higher frequency content also noted. Discrete foot force dosimeter and force plate AP and ML spectral data during ambulation have not been previously reported.