This lecture explains the basics of mechanism of walking
Outline of Lecture
Mechanism of walking
The line of gravity extends superiorly through the junctions of the curves of the vertebral column and inferiorly in a line posterior to the hip joints but anterior to the knee and ankle joints.
The position of the line of gravity, which is determined by the distribution of body weight, is important in determining the degree of muscular activity involved in maintaining all phases of posture
Few muscles of the back and lower limbs are active during the immobile periods.
When a subject is in the easy standing position, the hip and knee joints are extended and are in their most stable positions while the ankle joint is in less stable position.
Because the line of gravity passes posterior to the hip joint and anterior to the knee joint, the weight of the body tends to hyperextend these articulations.
At the hip this is resisted by the iliofemoral ligament and at the knee by the ligamentous apparatus of the knee and the action of the hamstrings.
Similarly, the generally anterior carriage of the weight of the body tends to cause dorsiflexion at the ankle joint, and this is resisted by contraction of the calf muscles.
These muscles, along with paraspinal muscles are the only absolutely essential muscles for maintenance of the upright posture.
Lateral stability in standing depends chiefly on the fascia lata, iliotibial tract, fibular collateral ligament of the knee, and tibialis anterior.
In locomotion (walking, running, jumping or climbing), there is an immediate departure from the economical pattern of standing.
All muscles of the trunk, arms and legs may be involved.
Arms are swung as balancers and also as weighted pendulums to increase the momentum.
Locomotion is very complicated.
When a subject is walking on level ground, the movements of the lower limbs may be divided into “swing” and “stance” phases, which are separated by heel-strike.
The swing phase occurs when the limb is off the ground, and the stance phase when it is in contact with the ground and is bearing weight.
A cycle of walking is the period from the heel-strike of one foot to the next heel-strike of the same foot.
This phase is a continuous process of weight transference from heel to toes, especially the hallux (big toe).
The whole body moves laterally towards the side of the leg in stance phase.
Centre of gravity is shifted and the arm on this side begins to swing forwards with the opposite leg.
Pelvis moves forward on the opposite side, accompanying the forward swing of the opposite leg.
With the foot fixed on the ground, the knee extends and the ankle dorsiflexes.
Tibia rotates medially followed by medial rotation at the knee and hip joints.
Maximum thrust is imparted by the plantar flexors of the foot.
Heel is raised and thrust is transmitted to the head of first metatarsal and the dorsiflexing big toe, terminating the stance phase.
At the time of heel-strike, the ankle is in slight dorsiflexion and the anterior leg muscles contract in order to prevent the forefoot from slapping down.
The muscles progressively relax to lower the foot and weight is transferred up the lateral side of the foot and then across the ball of the foot as the stance phase progresses.
The last part of the foot remaining on the ground is the medial part of the ball of the foot and the great toe.
This is termed “toe-off” and begins the swing phase.
At the time of heel-strike, the knee is slightly flexed on that side, with contraction of the quadriceps necessary to prevent collapse.
As the stance phase progresses, this knee straightens, resulting in some upward motion of the trunk.
During the stance phase, the thigh abductors, particularly the gluteus medius and minimus, are active on the side of the leg that is in contact with the ground.
This is in order to resist the tendency of gravity to cause downward movement of the hip on the opposite side.
Additionally, the paraspinal muscles and lateral trunk muscles are active on the side of the swinging leg in order to resist downward movement of the iliac crest on that side.
The center of gravity moves upward and downward twice during each cycle, as is indicated by the bobbing up and down of the head.
That is, the body is lifted as each limb is extended during its stance phase.
There is also a slight side-to-side movement.
The basic movements involved in walking are:
(1) flexion and extension at the hip, knee, and ankle joints and at the front part of the foot;
(2) abduction and adduction, chiefly at the hip joint; and
(3) rotation, mainly at the hip and knee joints.
In swing phase, toes leave the ground as the opposite heel meets it to transfer support.
The leg swings forwards with flexion at the hip and knee, dorsiflexion of the foot and lateral rotation of all those elements that had undergone medial rotation during stance phase.
The pendular action of leg is under the influence of hip flexors.
Momentum of the limb is overcome by hip extensors to bring the heel to the ground and to begin another cycle.
In all forms of progression, forces involved are gravitational, inertial and muscular.
Foot has two equally important functions:
Support the weight of the body in the standing or progression.
Act as a lever to propel the body forwards in walking, running or jumping.
When the foot is on the ground in resting position,body weight brings about some degree of supination with flattening of longitudinal arches.
One third of the body weight borne by the fore foot is carried through first meta tarsal.
When the position of rest is changed to the active position on commencing to walk, foot becomes pronated by muscular effort, the head of first metatarsal is depressed and the longitudinal arch is accentuated.
Therefore in order to propel the body forwards as in walking, running and jumping, foot should act as a strong and adjustable lever
Contraction of sloeus, gastrocnemius and plantaris is the chief factor responsible for propulsion in walking, running and jumping.
Action of these calf muscles is enhanced by arching of the foot and flexion of toes
In walking, the body weight is thrown forward and the weight is borne successively on the lateral margin of the foot and heads of metatarsal bones.
As the heel rises, the toes are extended at the metatarsophalyngeal joints and the planter aponeurosis is pulled on causing shortening of the tie beams and heightening the longitudinal arches.
The slack in the long flexor tendons is taken up thereby increasing their efficiency.
The body is thrown forward by the actions of gastrocnemius,soleus and plantaris on the ankle joint, using the foot as a lever and by the toes becoming strongly flexed by the long and short flexors of the foot, thus providing the final thrust forward.
The lumbricals and interossei contract and keep the toes extended so that they donot fold under because of the strong action of the flexor digitorum longus.
So the long flexor tendons assist in plantar flexing the ankle joint.
When a person runs the weight is borne on the forepart of the foot,and the heel does not touch the ground. The forward thrust to the body is provided by the mechanisms described for walking