Question

How can acceleration data be used to quantify gait?

Answer 1

Acceleration is the rate of change of velocity with time. While the term is often used to mean a state of increasing speed, any change in the velocity results in acceleration: increasing speed, decreasing speed, or changing direction. During routine walking, the body’s center of mass changes velocity in all three directions of motion (anteroposterior, mediolateral, and vertical) resulting in distinct acceleration profiles that are regular and repeatable from step to step. When an accelerometer is secured to the lower trunk, the recorded accelerations serve as a proxy for accelerations of the body’s center of mass and are hence indicative of global body control during walking. Any change in velocity of the center of mass occurring during a very short period of time results in a large acceleration; consequently, the lower trunk acceleration signal amplifies, or is sensitive to, even small, subtle changes in the control of the center of mass. During walking, lower extremity muscle activations accelerate and decelerate the body’s center of mass. Abnormalities in the timing and magnitude of muscle activations and force generation can cause aberrant accelerations/decelerations of the center of mass which in turn will be reflected in abnormal lower trunk acceleration profiles. Abnormal lower extremity muscle activations are evident even in active, healthy older adults walking at normal speeds; thus, abnormal lower trunk acceleration profiles are expected, and can reflect early, subclinical changes in global gait control in older adults.

Not only is acceleration a sensitive measure, it is a measure relatively easy to collect. Direct recording of 3D accelerations of the body during walking is typically achieved using a single triaxial accelerometer. Accelerometers are now small, low cost and wireless, enabling testing in real world environments, minimal set-up time, and the ability to walk naturally without hindrance.

There are many different ways of processing and analyzing the acceleration signal. As the interest in AGA increases, the number of ways researchers find to extract information and analyze the signal increases. Consequently, there are many acceleration measures used for gait analysis with a relatively small body of research investigating each measure. The processing required for many acceleration measures is complex, often necessitating a bioengineer or expert in signal processing be a key member of a clinical gait research team.

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