Gait analysis

Gait analysis is the systematic study of animal locomotion, more specifically the study of human motion. Instruments are used to measure the body’s information. Gait analysis is used to assess, plan, and treat individuals with conditions affecting their ability to walk.

It is also commonly used in biomechanics to help athletes run more efficiently and to identify posture-related or movement-related problems in people with injuries.

Borelli was the first one who researched Biological Kinematics in 1680. Because of the equipment was not fine and the knowledge was not enough at that time, the result of the research was not very well. In 1895, Braune and Fisher started the research of modern biomechanics, they also introduced into the study of life movement the technique of stereometry, of stereophotogrammetry in particular, which today is still the basic experimental technique in biomechanics of human movement. In 1984, Cappozzo introduce a VICON system equipped with three TV cameras and force plate positioned as shown in Figure 2.3(a). Figure 2.3(b) shows the marker configuration and embedded coordinate systems in VICON system. Among them, 𝑃₁, 𝑃₂, 𝑃_3, are the markers on coordinate systems in Kadaba’s research. In the Figure 2.3(d), two markers are placed on the right and left ASISs. One other marker is placed on a 10 cm long stick extending from the top of the sacrum (L4-L5) in the spinal plane. Other markers are placed on the following locations of the particular limb under consideration: greater trochanter, rotation axes of the knee joint, shank lateral malleolus, and foot thumb. They find 40 normal

healthy testers with no previous history of musculoskeletal problems and measure the rotation of pelvic, hip joint, knee joint and ankle rotation. In this paper, we only discuss the result of hip joint and knee joint, because our design only contains hip joint to knee joint. Figure 2.4 shows the rotation of hip joint and knee joint. In Figure 2.4 (a) to (c), rotations of flexion/extension, adduction/abduction and internal / external rotation of the hip joint are shown respectively. Figure 2.4 (d) to (f) show the rotations of flexion/extension, varus/valgus and internal rotation, external rotation of the knee joint respectively. As the result, we can know the limit in rotation of hip and knee joint. In the rotation of hip joint, maximums of flexion, extension, adduction, abduction, horizontal adduction, and horizontal abduction are about 30°, 10°, 5°, 5°, below 5°, below 5°, respectively. In the rotation of knee joint, maximums of flexion, extension, varus, valgus, internal rotation, and external rotation are 60°,0°,5°,0°, below 5°, below 5°, respectively.

Figure 2.3 Method of gait analysis (a) Stereo metric set up and force plate in Cappazzo research [27]. (b) Marker configuration and embedded coordinate systems in Cappazzo research [27]. (c) Stereo metric set up and force plate in Kadaba’s research [28]. (d) Marker configuration and embedded coordinate systems in Kadaba’s research [29].

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Figure 2.4 Mean (thick line) and one standard deviation (dotted lines) of hip and knee rotation (a) Hip flexion and extension (b) Hip adduction and abduction (c) Hip internal and external rotation (d) Knee flexion and extension (e) Knee adduction and abduction (f) Knee internal and external rotation

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2.1.3 Design target

After discussing the results, we can get a gait cycle, as shown in Figure 2.5(a) in which there are two phases of the gait, double support phase and single support phase. There are also two phases in single support phase, stand phase and swing phase. And then the actual degrees with gait cycle as shown in Figure 2.5(b). Later, we combine the coordinate systems of joint with these gait analysis and design our assist device.

Hip joint is a ball and socket joint with three degrees of freedom, which include rotation of flexion/extension, adduction/abduction and internal / external rotation.

Although hip joint is a ball and socket joint, we couldn’t design ball and socket joint on the device as hip joint. The assist device is mounted on the human body, and can’t be the same as the hip joint in the human body. In order to design a hip joint in our assist device to fit in with the hip joint of human body, we design two axes like the axes of 𝑒₁ and 𝑒₂ in hip joint coordinate system which defined by ISB above. Axis 𝑒₁ is perpendicular to the sagittal plane, and axis 𝑒₂ is perpendicular to the frontal plane. We made two axes extend and cross the center of hip joint in the human body and they are perpendicular to each other. According to this condition, the motion of the hip joint on assist device can confirm the motion of human’s hip joint as shown in Figure 2.5(c). We ignore the axis 𝑒₃ here, because the rotation on axis 𝑒₃ is very small. The value which is below 5^° is the minimum in all rotation of the hip joint. Also, if we want to design the axis 𝑒₃ and confirm the motion of human’s hip joint, axis 𝑒₃ needs to extend and cross with 𝑒₁ and 𝑒₂ at the center of hip joint in the human body. With the statement above, it is really hard to design an axis whose rotation is so small on axis 𝑒₃ extending to hip joint on assist device, so we don’t design it.

As for the knee joint which is a hinge joint with slide degree of freedom, we don’t care about the slide motion and don’t use the motor on knee joint in order to simplify the design. In our design, we provide the assist device to the elderly who have the ability to walk. So we don’t need the motor to control the knee rotation. We use a hinge joint to fit in with the knee rotation, which follows the rotation of human knee. In particularly, we design a sliding groove and slider mechanism for preventing falling on knee.

Preventing falling mechanism is combined with the gait analysis and the detail will be described later.

Figure 2.5 Gait cycle (a) Human walking cycle which is divided into single support phase and double support phase [29]. (b) Human's right leg walking cycle with actually degrees [30]. (c) Design purpose on hip joint.

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Rotation point (hip joint)

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Axes e₃