Mechanism of movements of muscles involved in walking

Walking is called an automatically performed act of movement, which is accomplished through a complex coordinated interaction of the skeletal muscles of the trunk and legs. This process consists of separate steps which represent a simple locomotor cycle which has basically two phases:

• Transporting.
• Supporting.

The transporting phase involves moving the foot a certain distance from its previous position. In the supporting phase, the human foot touches the ground surface. The initial stage of transfer of the foot forward includes the following motor acts (Fig. 1A):

• Implementation of flexion of the hip joint with the effort of the lumboinguinal muscle.
• Flexion of the leg in the knee joint with the help of coordinated muscle action: the biceps femoris and a group of ischiofemoral muscles (semimembranous, semitendinosus muscles, and long and short heads of the biceps femoris).
• Implementation of ankle bending with the flexor muscles of the ankle and anterior tibial muscle, as well as the tertiary peroneus muscle.
• Extension of the toes by the protractor muscles (extensor digitorum longus, extensor hallucis longus, extensor digitorum brevis, abductor hallucis brevis).
• During the initial touch of the foot with the surface, the following processes occur (Figure 1B):
• The flexion of the hip joint ends with the lumboinguinal muscle.
• Extension of the knee joint with the quadriceps femoris muscle.
• Completion of the flexion of the ankle by the toes rectifier muscles and flexors of the ankle.

At the completion of the process of carrying the foot and the appearance under it of a reliable support, the quadriceps femoris activates, as well as the beginning of the operation of the gluteus maximus muscle (Fig. 1C).

Fig. 1. The process of human movement

Then the phase occurs, during which the human body moves forward. This stage includes the following processes (Figure 2A):

• Extension of the hip joint with the effort of the large gluteus muscle and the ischiofemoral muscles.
• Antagonism-synergism with quadriceps femoris.
• Synergistic flexion with flexor muscles and a gluteus maximus muscle of the ankle.
• During the initial motor impulse preceding the support of two legs, the following processes occur (Fig. 2B):
• Continuation of extension of the hip joint with gluteus maximus muscle and ischiofemoral muscles.
• Continuation of knee extension with quadriceps femoris.
• Extension of the ankle by biceps femoral muscle and flexors of the toes (flexor digitorum longus, flexor hallucis longus of the foot and musculus flexor hallucis brevis, flexor digitorum brevis).

The second stage of the motor impulse, which acts on the supporting limb of the man in the fully extended state, while the transferred leg is about to come to the floor, is characterized by the increased action of the quadriceps femoral muscle, gluteus maximus muscle, the muscles of the ischiofemoral group, the biceps femoris and muscle flexors of the toes (Fig. 2C).

The peculiarity of the beginning of movement from one supporting leg to the other is the accelerated transfer of the limb under the action of the muscles of the ischiofemoral group and the flexor muscles of the ankle, as well as the flexion of the hip joint with the muscles of the lumboinguinal group (Figure 2D).

In the anterior part of the limb, when it is transferred, there is an increased effect of the lumboinguinal and the quadriceps femoris with simultaneous relaxation of the muscles of the ischiofemoral group. The knee is extended in parallel by the effort of the quadriceps femoris muscle and lifting of the toes with the extensor muscles of the toes (Figure 2E). After that, the cycle is repeated again [1,2,3,4,5].

Fig. 2. Phases of movement

The process of walking involves not only the muscles of the lower limbs, but also other muscle groups.

The movement of the leg is accompanied by an inclined position of the human body, which is achieved by the effort of the muscle group of the back of the body. This process involves the following muscles:

1. Trapezoidal.
2. Broadest muscle of back.
3. Dorsal rhomboid muscle consisting of a rhomboid major muscle and a rhomboid minor muscle.
4. Muscles extending the spine.
5. Longissimus dorsal muscle.

In order for the body not to fall backwards, during the rear movement, the muscle groups of the anterior surface of the trunk and abdomen become involved:

• Abdominal rectus muscle.
• External abdominal oblique muscle.
• Internal abdominal oblique muscle.
• Transverse abdominal muscle.
• Lumbar quadrate muscle.

These same groups of muscles are used when it is necessary to fix the pelvis, which provides support for the movement of the lower limb.

It should be noted that during the transfer of the leg, the body together with the pelvic department performs a turn along the vertical axis towards the supporting limb. This movement is implemented with the help of the internal abdominal oblique muscle and the external, transversospinal muscle and iliopsoas muscle, opposite to it.

In order to avoid deviation of the human body to one side during the movement, the muscles that straighten the spine and the longissimus muscle of the back are used.

In some situations, the muscles of the rear side of the neck can be contracted. Also, when a person is walking, the following muscles of the trunk are involved:

• Posterior scalene muscle.
• Elevator muscle of scapula.
• Musculus serratus posterior superior.
• Splenius muscles of head and neck.
• Semispinalis capitis muscle.
• Semispinal muscle of the neck.

When walking, the muscles of the arms do not practically strain. Only the flexor muscles of the shoulders and partly the elbows are involved during the forward movement, and the extensor muscles of these joints when moving backward.

The flexor muscles of the shoulder joint include:

• The anterior part of the deltoid muscle.
• Large pectoral muscle.
• Coracohumeral muscle.
• Biceps muscle of arm.

The extensor muscles of the shoulder joint include:

• Posterior part of the deltoid muscle.
• Broadest muscle of back.
• Infraspinatus muscle.
• Teres minor muscle.
• Teres major muscle.
• Long head of triceps brachial muscle.

Shoulder flexion muscles:

• Brachial muscle.
• Muscles of the brachioradial group.
• Biceps brachial muscle.
• Long protractor muscle of the wrist joint.
• Muscles of the elbow.
• Round pronator muscle.

The extensor muscles of the elbow joint include the triceps brachial muscle.

The free upper limb acts as a pendulum during walking. This is achieved by alternating effort of different parts of the deltoid muscle.

If all the above muscle groups function normally, then the person does not have difficulty when walking or running. But there are very few such people in the world, as most muscles are swollen to varying degrees of severity in the majority of people. Due to that the muscle tissues are not able to stretch to the physiological norm.

In non-stretchable muscle fibers, the movement of cell nuclei to certain zones is observed, as well as a decrease in the number of mitochondria, which are the elements that produce energy for the work of muscles. Depending on the degree of damage to particular muscles, the patient may exhibit various movement defects: abnormality of the gait, unevenness of the lower limbs, tarsoptosia, walking on tiptoe, curvature of the spine.

Here is an example of how the muscles of the back, as well as the upper and lower extremities do not move because of tetraparesis, which is one of the forms of infantile cerebral palsy.