Locomotion and Gait
Locomotion is described as the ability to move from one position to another. Gait, on the other hand, is defined as the style or manner of walking dependent on a complex interplay of major parts of the body systems including the nervous system, musculoskeletal system, and cardiovascular system. Moreover, locomotion encompasses gait, with the overarching goal of maintaining stability through a progression of the center of gravity within the base of support, while utilizing the least amount of energy as possible..
The Gait Cycle
Locomotion and gait are produced by a series of predictable joint movements (kinematics) and forces (kinetics). Additionally, these movements and forces work together and can be summarized into a consistent sequence known as the gait cycle.
The gait cycle consists of two phases: Stance phase, in which the reference limb is in contact with the ground, and swing phase, in which the reference limb is not in contact with the ground. Stance phase involves closed chain (compression) mechanics and comprises 60% of a single gait cycle while swing phase involves open chain (suspensory) mechanics and comprises the other 40% of a cycle. The phases of gait are as follows:
Suspension mechanics vs. Compression mechanics
In general, the forces of the gait cycle encompass a perpetual balance between outside forces including gravity and ground reaction, and internal muscle forces. Furthermore, each phase of the gait cycle involves different forces working on the individual segments and can be broken down further into compression or suspension mechanics.
Compression occurs when the leg is in contact with the ground and involves increased tension of ligaments, muscles, and fascia compressing the joints and decreasing space to improve stability. The major muscles involved in compression mechanics include the gluteus maximus on the ipsilateral (same) side, and the latissimus dorsi on the contralateral (opposite) side. Weakness in either of these muscles consequently leads to dysfunction and instability.
On the contrary, suspension mechanics occur when the leg is not in contact with the ground. During this phase there is greater space between the joints and involves more mobility with less stability. Major muscles involved in suspensory mechanics include the hip flexors, quadratus lumborum, and spinal extensors.
In development, motor skills and coordination progresses in a proximodistal fashion, or in other words, from midline outward. Moveover, muscles in the thorax and abdomen develop first to maintain stability and provide a stable foundation for limb movement. For example, a child must first develop the ability to stabilize and hold their head against gravity, then they must develop their abdominal musculature through rolling and sitting, then they will progress to standing and finally active limb movement. This development continues and becomes more refined and reflexive over time, and is evident in movement patterns such as gait.
How is Gait Controlled
Human bipedal walking is controlled by high level central nervous system regions and central pattern generators (CPGs) located in the spinal cord which create a rhythmic pattern of flexor and extensor muscle force generation. These CPGs are furthermore impacted by feed-back and feed-forward control. Feed-forward control involves predetermined timing and force predictions in order to create an efficient and accurate movement. In other words, feed-forward mechanics involve repetitive learning and pattern recognition throughout development. Feed-back control involves the body’s response to external perturbations and subsequent adjustment. For example, if one steps in a hole during normal walking, proprioceptive input will react accordingly to adjust muscle force and activation to adapt to the changing environment. In general, normal locomotion is achieved through a combination of balanced input from both feed-forward and feed-back control.
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