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Physiology of Walking

For medical students2 min readUpdated 2026-10-10

Walking is a complex behavioral activity divided into discrete motor "quanta." It is ensured by strict coordination of flexor and extensor muscles under the control of various levels of the nervous system.

"Pillar Leg" PhenomenonSimultaneous contraction of antagonists makes the support leg rigid before taking a step
BrakesThe biceps femoris muscle stops limb movement at the end of the swing phase
Pace EffectAcceleration of the step occurs exclusively due to the shortening of the stance period
ControlStep length and cadence are controlled by cortical and brainstem structures

Neurophysiological Basis and Regulation of Locomotion

The physiology of walking is based on a complex system of connections between neurons located in various segments of the spinal cord. This spinal network provides basic coordination—the timely and alternating contraction of flexor and extensor muscles.

Higher control over locomotion is exercised by cortical and brainstem structures. They are responsible for adapting movements, in particular, regulating step length and the frequency of muscle contractions. Descending motor pathways running from the brain to the spinal cord are functionally divided into two separate systems. Each of these systems assumes control over strictly defined muscle groups involved in moving the body through space.

Cyclicity and Periods of Walking

Movements during walking are not chaotic; they form a strict, constantly repeating sequence—the gait cycle. This cycle consists of alternating periods that smoothly transition into one another:

  1. Double-support period: the initial phase in which both feet simultaneously contact the support surface.
  2. Asymmetrical phase: the left leg enters the single-support period (bears weight), while the right leg is in the swing period (moves forward).
  3. Second double-support period: a brief return to support on both limbs.
  4. Role reversal: the right leg enters the single-support period, and the left leg performs the swing.

Interestingly, when changing pace (acceleration), the total duration of the cycle naturally decreases. However, this reduction occurs unevenly: time is saved exclusively by decreasing the stance period, while the duration of the swing phase remains practically constant.

Biomechanics of Periods: Stance and Swing

Each period of the walking cycle is characterized by a unique pattern of muscle activity and biomechanical changes.

Stance Period (The "Pillar Leg" Phenomenon) In this phase, the trunk rests on the limb, and the leg straightens completely, bearing the body's weight. Key roles are played by:

Right before placement on the support, both flexors and extensors are activated. Their simultaneous (cocontraction) gives the leg maximum rigidity, turning it into a reliable support—a pillar.

Swing Period This phase combines active and passive biomechanical processes:

Of particular importance is the completion of the swing phase. To prevent the leg from continuing to move forward by inertia, a sharp contraction of the m. biceps femoris occurs. It acts as a physiological brake, stopping limb movement right before it contacts the support.

Mnemonic

To remember acceleration biomechanics: imagine the ground becomes "hot" when running. You try to lift your foot faster (shortening the stance period), but the flight time of the leg in the air (swing) remains stable.

Frequently asked questions

Into what two separate systems are the descending motor pathways controlling locomotion divided?

Descending motor pathways of the spinal cord are functionally divided into two systems controlling different muscle groups during walking.

  • Medial motor system — innervates motor neurons lying more medially in the ventral horns of the spinal cord; is primarily responsible for movements of the trunk and legs, ensuring standing and walking.
  • Lateral system — is responsible for smooth and precise movements of the forearms and hands.
What spinal centers and generators form the locomotor rhythm (stepping reflex)?

The flexion phase during locomotion is largely determined by the spinal locomotor generator. There are several such generators for each limb; their work is rapidly adapted under the influence of afferent impulses entering the spinal cord.

At the spinal level, the following participate in transmitting motor commands:

  • spinal interneurons — intermediate links through which many descending pathways switch to motor neurons;
  • alpha motor neurons of the spinal cord — the "final common path" innervating skeletal muscle.

During voluntary stepping, initial commands come from the motor areas of the cerebral cortex directly to the motor neurons of flexors and extensors.

Why does the walking cycle shorten when accelerating pace?

During acceleration, the cycle duration shortens only due to a decrease in the stance period. The time of the swing phase remains practically constant.

Which muscle stops the leg at the end of the swing period?

The forward movement of the leg before ground contact is stopped by the contraction of the biceps femoris muscle (m. biceps femoris).

What is the essence of the "pillar leg" phenomenon?

This is a biomechanical state in which the simultaneous contraction of flexor and extensors makes the leg rigid to reliably support the weight of the trunk.

Which parts of the CNS regulate step length and cadence?

These motor activity parameters are controlled by cortical and brainstem structures of the brain.

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