A portable system with sample rate of 250 Hz for characterization of knee and hip angles in the sagittal plane during gait

Abstract

BackgroundGait analysis and research have been developed to obtain characteristics of movement patterns of people while walking. However, traditional measuring systems present different drawbacks that reduce their use and application. Among those drawbacks one can find: high price, low sampling frequency and limiting number of steps to be analyzed. Traditional measuring gait systems carry out their measurement at frequencies oscillating between 60 to 100 Hz. It can be argued about the need of higher sampling rates for gait measurements. However small displacements of the knee or hip for example, cannot be seen with low frequencies required a more detailed sampling and higher frequency sampling. Bearing this in mind, in this paper is presented a 250 Hz system based on accelerometers for gait measurement, and the particularities of knee and hip angles during gait are highlighted.MethodsThe system was designed with a PCI data acquisition card instrumented with an FPGA to achieve a rate sample of 250 Hz. The accelerometers were placed in thighs and legs to calculate the joint angles of hip and knee in the sagittal plane. The angles were estimated using the acceleration polygon method without integrating the acceleration and without filters.ResultsThe gait of thirty healthy people of Mexican phenotype was analyzed over a flat floor free of obstacles. The results showed the gait phases and particularities associated with the walking style and people's laterality; the movement patterns were similar in the thirty persons. Based on the results, the particularities as the maximum amplitude in the angles and the shape in the movement patterns were related to the anthropometry and people phenotype.ConclusionsThe sampling frequency was essential to record 340 samples in single gait cycle and so registering the gait cycle with its particularities. In this work were recorded an average of 8 to 10 gait cycles, and the results showed variation regarding works carried out in biomechanics laboratories; this variation was related to the method and reference frame used to obtain the joint angles and the accuracy of measurement system.

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“…Some of the important specifications for an accelerometer include its sensitivity, sampling rate and maximum swing. 22 Sensitivity refers to the change in measured output for any given unit of change in the measured signal, and it is measured in millivolts per gravity. Generally, the more sensitive the accelerometer, the better it is.…”

Algorithm to estimate the knee angle in normal gait: trajectory generation approach to intelligent transfemoral prosthesis

“…La Tabla 1 muestra datos antropométricos y fenotipo de los sujetos analizados. Para el análisis se utilizó la metodología y sistema de medición, instrumentado con acelerómetros, reportado en [23].…”

“…Se colocaron dos acelerómetros en cada miembro inferior como se muestra en la Figura 2(b). La estimación de ángulos articulares de cadera (q1) y rodilla (q2) se llevó a cabo mediante el polígono de aceleraciones reportado en [23]. Durante el análisis de marcha, cada sujeto registró entre 7 a 9 ciclos.…”