*2.2.3 Changes in movement at the ankle*

*Assistive and Rehabilitation Engineering*

the lower limb.

the gait speed.

healthy subject whatever their gait speed.

*2.2.1 Changes in movement at the hip*

*2.2.2 Changes in movement at the knee*

**2.2 Changes in joint kinematic parameters**

showed that the cadence of the stroke patients is decreased compared to those of the

The modifications of spatiotemporal parameters observed during gait of stroke patients are mainly caused by kinematic and kinetic alterations [19]. Global motor organization is given by the kinematic parameters, a segment rotation is characterized in function of the adjacent one, and joint angles are the main elements allowing the understanding of the gait. **Figure 2** illustrates the definition of joint angles of

The joint angle of the hip is defined as the relative angle between the pelvis and the femur. The flexion/extension of the hip occurs in the sagittal plane. The flexion of the hip propels the thigh toward the anterior surface of the body. In contrast, the exten-

For the healthy subject, at the beginning of a cycle, the hip is in flexion. During the single support phase, the hip performs an extension. At the end of propulsion, the angle of the hip reaches a maximum extension of about −10°. During the oscil-

Usually, a stroke patient exhibits both an insufficient hip flexion and a limitation of the hip extension, [20] which contribute to the decrease of the step length and of

The joint angle of the knee, defined as the relative angle between the tight and the shank, is close to +10° for the healthy subject at the beginning of a gait cycle. During the single support phase, this angle increases to a first maximum amplitude of about +20° and then decreases. At the beginning of the oscillating phase, the knee flexes quickly to prepare the oscillation of the body. We then observe a second

local maximum with a value that can reach +60° followed by an extension.

sion of the hip throws the thigh toward the posterior surface of the body.

lating phase, the maximum value of hip flexion can reach +45°.

**142**

**Figure 2.**

*Definition of the joint angles for the lower limb.*

The ankle joint angle is defined as the relative angle between the shank and the foot, the foot being considered as a single rigid segment. The dorsiflexion of the ankle in the sagittal plane traduces a flexion of the foot. In contrast, plantar flexion comes from a flexion of the foot.

During the gait cycle, the evolution of ankle angle is composed by three steps:


In stroke patients, a plantar flexion is often observed either during the initial double contact or during the single support phase or the swing phase. This decrease of dorsiflexion can be explained by a spasticity of the triceps surae muscle. This phenomenon is often associated with a reduction of the propulsive force and a deficit of the gait velocity [21, 22].
