When we walk forward, we can see a rhythmic alternating movement of our two lower limbs. In each lower limb, there are five main joints (hip, knee, ankle, subtalar and metatarsophalangeal) that contribute to the gait cycle under the selective control of 28 major muscles.
Gait cycle
The gait cycle can be simply stated as the manner of walking. It is a repetitive pattern involving steps and strides. The gait cycle is described with a single limb. The reciprocal action of the two limbs is timed to trade their weight-bearing responsibility during the period of double stance.
The double stance period is the time both feet are in contact with the ground. It usually occurs in the initial and terminal 10% intervals of stance. The middle 40% is a period of single stance. During this time the opposite limb is in the swing. One limb typically provides support while the other limb is advanced and it will take the role of the supportive limb when it touches the ground.
The Gait cycle endlessly blends into the next. So, we can select any event as the starting point. Normally we select initial floor contact as the first event because it is the most consistent event in both normal and abnormal gait.
Phases of the gait cycle
Stance Phase
Swing Phase
During the normal gait cycle, approximately 60% of the time is spent in stance and 40% in swing. These percentages can be varied with the walking speed and among the individuals.
Stance Phase
This is the period of weight-bearing. It consists of the initial contact stage, loading response, mid-stance stage, terminal stance, and pre-swing stage.
(1️) Initial contact/Heel-strike stage
This is the stage at which the walker is most stable. In this stage, the heel of the first foot makes initial contact with the floor. This is a momentary posture. In this stage, the foot is at a 25° angle to the floor. The ankle is in an approximately neutral position. The knee is extended between 0°-5° of flexion and the hip is flexed 30°. Dorsiflexsors, hip flexors, gluteus, and hamstring muscles are used for heel-strike.
With the heel-strike, the leg has to accept the weight of the body. This so called loading response. Marks the first 10% of the gait cycle. The loading response endsonce contralateral foot lift off the ground.
(3️) Mid-stance stage
In this stage, only one foot is in contact with the ground and it is flat on the ground. The foot takes the weight of the body and the body carries the weight forward. At the onset of a single stance, the ankle is still slightly plantarflexed. From this position, there is gradual dorsiflexion. Knee flexion induced during the loading response increases slightly. The motion of the knee then reverses to the progressive extension. Hip extensors are used for this stage. The knee is also slightly flexed. The body is least stable at this point. Soleus, gastrocnemius, quadriceps, and hip abductors are the muscles used for this stage. This is 20% of the gait cycle.
(4️) Terminal stance stage
The heel is taken off from the ground at this stage. The toes push up to lift the whole foot, clearing the foot off the floor. In this stage, the body's center of gravity drops slightly during advancement. At the onset of a heel raise the ankle drops into the maximum dorsiflexion occurring instance. Strong dorsiflexion torque is generated through the midfoot. Stability is gained by inversion. The knee is extended passively by the forward alignment of body weight. The hip is also extended. Soleus, gastrocnemius, tibialis posterior, peroneus longus, and peroneus brevis are the muscles used for this stage. This is 20% of the gait cycle.
(5️) Pre-swing stage
The leg lifts further off the ground. This is called pre-swing. Preparation of the limb for the swing is the purpose of the actions that occur during the pre-swing phase. Floor contact by the other foot initiates this interval of terminal double support.
This is 10% of the gait cycle.
At the end of the stance phase, both feet are in contact with the ground.
Swing Phase
This is an interval of self-advancement. This stage occurs after the pre-swing phase. The lifted limb moves forward and it shortens. This stage consists of the initial swing stage, mid-swing stage, and terminal stage.
(1️) Initial swing stage
This is the initial part of swinging. Both the knee and the hip are flexed. Hip rapidly flexes to 20° from the neutral position. Dorsiflexion of the ankle is initiated. The muscles contracting quickly to lift the foot are tibialis anterior, long-toe extensors, and peroneus tertius. The force that needs to move the limb forward is produced by the hip flexors. This is 13% of the gait cycle.
(2️) Mid-swing stage
In this phase, the limb passes the stance limb. At this time the limb is at its shortest. As limb advancement continues, the changes in the tibial alignment make foot control for floor clearance. The hip is at its maximum flexion to 30°. Relaxation of the flexor muscles allows the knee to extended passively. The ankle becomes neutral from dorsiflexion. Iliacus, tibialis anterior, and other pretibial muscles are used for this stage. This is 14% of the gait cycle.
(3️) Terminal swing stage
This is the terminal part of swinging. Forward movement of the limb is slowed down to position the foot for the heel strike. The critical event is complete knee extension. The 30° of hip flexion attained in midswing is maintained. The knee is extended. Ankle continues basic posture, but the foot may drop into slight plantar flexion at the end. The lower limb muscles help to control this. Semimembranosus, semitendinosus, biceps femoris, quadriceps, and hamstrings are the muscles used for this stage. This is 13% of the gait cycle.
Some special words related to the gait cycle
Step - A single step.
Stride - The whole gait cycle.
Step time - Time between the heel-strike of one leg and the heel strike of the contralateral leg.
Step width - The mediolateral space between the two feet.
Step length -The distance between the one heel strike to other heel strikes.
Stride length - The distance between the heel strike of one limb to the next heel strike of the same limb.
Fazmiya Noordeen
References
http://www.oandplibrary.org/alp/chap13-01.asp
https://www.physio.co.uk/what-we-treat/neurological/symptoms/walking-problems/abnormal-gait.php
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