Page 15 - Maximizing the efficacy of ankle foot orthoses in children with cerebral palsy

Adequate functioning of the ankle and foot is essential for normal walking, and can be described in terms of rockers[15]. The first rocker, also called heel rocker, represents the time span from the first heel contact (i.e. initial contact) to full contact of the foot with the surface. This involves lowering of the foot to the surface, which is controlled by eccentric contraction of the ankle dorsiflexor muscles. During the second rocker (ankle rocker), the tibia progresses over the foot, which remains flat on the ground. This is due to an eccentric contraction of the ankle plantar flexor muscles and allows continued forward movement of the body. The third rocker (forefoot rocker) represents the phase from contralateral initial contact to toe-off At this stage, a large burst of power is generated about the ankle, which is due to a fast shortening (concentric contraction) of the plantar flexor muscles resulting in plantar flexion movement.
In addition to sufficient rocker functions, knee joint function in the sagittal plane is also considered an important feature during gait. The knee acts like a shock absorber as it flexes during early stance, while maximal extension is reached just before contralateral initial contact occurs. Using the force of the plantar flexion during the third rocker (push- off), and psoas muscle activation, the knee and hip will flex to reach sufficient clearance of the foot during the swing phase.
Normal gait is a complex yet highly energy efficient process[16]. Several biomechanical adjustments are used by the body to minimize the energy consumption [J·kg·min-1] during walking, such as a minimal excursion of the center of mass, and transfer of energy between segments by bi-articular muscles[16]. The energy consumed in relation to the covered distance is also dependent on a person’s walking speed, expressed by the energy cost of walking [J·kg·m-1] (also referred to as gait efficiency) and calculated by dividing the energy consumption by walking speed. Healthy individuals select a comfortable walking speed at which gait efficiency is maximal[17]. In healthy children, gait efficiency improves with age until adulthood[17,18].
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General introduction
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