The swing leg phase is one of the main components of gait pattern. Functional limitations of the range of motion can significantly reduce the range of motion.
What is the swing leg phase?
Swing leg phase describes the range of motion of the free leg during walking and running. The swing leg phase describes the range of motion of the free leg during walking and running. Together with a stance leg phase, this results in a gait cycle. The swing leg phase can be divided analytically and functionally into 3 sections, the early swing phase, the middle swing phase and the terminal swing phase. It begins with the lifting of the leg after the stance leg phase. In this phase, the thigh is lifted by the hip flexors and the lower leg is lifted by the knee flexors; the foot initially remains passive. In the middle phase, the leg is moved forward through increased hip flexion while the knee is loosely brought to vertical. The toes and foot are actively lifted so that they can be brought forward above the ground. In this phase, flexion in the hip joint reaches its greatest extent. In the terminal stance leg phase, the leg is lowered back toward the ground. At the same time, the knee is actively extended and the foot is held in neutral in preparation for the upcoming contact of the heel with the ground. A functionally important accompanying component is the forward co-rotation of the pelvis.
Function and task
The swing leg phase is important for gaining space while walking. While forward movement of the entire body occurs on the stance leg side, simultaneous transport of the free leg on the swing leg side ensures that the next step can be continued with gain of distance. The movement components of the swing leg phase are designed at a normal walking pace to create a fluid gait pattern with minimal effort. Hip flexion is relatively low in all phases and the foot is lifted only a few centimeters off the ground. Only the knee joint is relatively flexed in the first phase, but only for a short time. The main work for the forward movement is done by the hip flexors, while the knee flexors at the beginning and the extensors of the ankle and toes in the middle show holding and braking muscle activity, respectively. In the terminal swing leg phase, the knee extensors then become active and the hip flexors control the adequate lowering of the leg. An increase in movement tempo leads to an accentuation of all movement components. This can be observed very clearly in sprinters. Especially hip flexion reaches much higher degrees of movement than in normal walking and the foot is pulled up significantly from the beginning. Overcoming heights also requires more flexion in the hip joint and greater extension in the foot and toes, while both components are decreased when walking on a sloping road. The amplitudes of motion are also affected by stride length, which in turn depends on relative leg length. With small strides, the swing leg phase lasts only a short time, so there is little time for execution. For this reason, the range of motion in hip and knee flexion in the early and middle phases is less than with normal stride length. Conversely, with long strides, flexion in the hip joint in particular is increased. At the same walking speed, the step frequency also changes with the step length. It is higher with short strides than with long strides.
Diseases and complaints
The muscles that are active in the swing leg phase must exert enough force to perform the movement in a coordinated manner against gravity. Any conditions that result in a reduction in strength, a complete loss of strength, or incoordination will impair the swing leg phase or totally prevent its execution. Herniated discs can lead to a lesion of the sciatic nerve, which supplies the foot jacks with one of its branches. If these muscles fail, the foot and toes can no longer be lifted and the toes drag across the ground in the swing leg phase. This increases the risk of injury from stumbling and falling, especially if sensitivity in the foot is also disturbed. Often, a compensatory mechanism can be observed in affected people to avoid this danger, the so-called stepper gait. This involves lifting the thighs significantly more than normal in order to get the hanging foot high enough off the ground and to be able to move the leg forward without dragging.Central nervous system diseases or injuries may affect all muscles involved in the swing leg phase. Paraplegia above the 3rd lumbar vertebra leads to a failure of the hip and knee flexors, the knee extensors and all foot muscles. Forward swinging of the leg is no longer actively possible. In a spastic pattern resulting from a stroke, the swing leg phase is significantly altered. Movement is initiated via the pelvis and the leg, which is extended at the knee and ankle joints, is set forward via a circular motion (circumduction). Ataxic gait disorders, such as in multiple sclerosis, first cause a feeling of insecurity in the stance leg phase. Therefore, affected people often do not dare to lift the leg for a long time in the swing leg phase. Short wobbly steps result. Another neurological disease affects the swing leg phase in a completely different way. In Parkinson’s disease, the phenomenon can often be observed that when walking, the steps become smaller and smaller and finally stop completely. Sufferers remain frozen in place. In this case, a visual or acoustic stimulus can be the impulse to resume walking. Injuries have a negative impact on the execution of the swing leg phase due to pain or restricted movement. A strain or muscle fiber tear of the hip flexors causes the period of activity of these muscles to be kept relatively short. The leg is brought forward quickly and briefly to end the pain that is exacerbated by the strain. Extension deficits in the knee due to osteoarthritis or surgery shorten the terminal swing leg phase.
