Biomechanics and Neural Control of Human Locomotion
Biomechanics of Walking and Running
Walking involves movements where the body alternates movements on opposite sides.
Description of the Action of Walking
Walking consists of two major phases:
- Stance Phase: One or two legs are on the ground, providing support.
- Swing Phase (Balance): One leg is off the ground, moving forward.
Transition from Walking to Running
The transition from walking to running occurs involuntarily, usually at a consistent speed determined by leg length, approximately 2.5 m/s.
There is a moment when walking requires more energy expenditure than running. At this critical velocity, the body stops walking and starts running.
Common Features of Locomotion Patterns
- Walking: A controlled fall (we stand and then sink).
- Running: A controlled fall where we utilize a stronger rebound. We jump and bounce because of inertia, and muscles act like springs (contracting and releasing stored energy).
Balancing changes very little; it is almost constant in both walking and running.
Ballistic vs. Non-Ballistic Movement
Walking involves both ballistic and non-ballistic phases.
- Ballistic Movement: Programmed before starting it (e.g., strength and stride). This movement is performed in an open loop (e.g., balance during walking or running).
- Non-Ballistic Movement: Controlled during execution. Standing is non-ballistic and performed in a closed loop.
Advantages of Ballistic Movement
Ballistic movement is faster and more comfortable because it requires less conscious control or planning. It occurs like a spring action and usually generates greater force.
Example: The hip joint movement during walking is ballistic; turning a wheel is non-ballistic.
Advantages of Non-Ballistic Movement
Non-ballistic movement can be controlled, allowing for the correction of errors on the fly.
Synergies in Locomotion
Walking involves a number of synergies—several movements that tend to occur together, even if seemingly unrelated (e.g., closing your eyes when sneezing). This also includes the movement of the arms when walking. Furthermore, the knee angle and the head angle are correlated.
Walking is a normal and smooth movement thanks to these synergies (e.g., demonstrated by angle-angle diagrams showing knee flexion/extension and foot balance).
2. Neural Control of Locomotion
It was previously unknown how the Nervous System (NS) regulates the physiological aspects of walking.
The rate of rhythmic movements (contractions and bending) occurs in the spinal cord (medulla) because it is more related to simple reflexes.
Rhythmic movements can be produced without the brain, but the cerebellum and visual information are necessary for equilibrium.
Hypothesis of the Chain of Reflexes
The rhythm that produces the action of walking was hypothesized to be caused by a series of chained reflexes (E1 R1 E2 R2 E3 R3…).
It was thought that movement was produced solely through a chain of reflexes. The stimuli that control the rhythm of walking are sensory and proprioceptive, originating from muscles and tendons.
Sensory information enters the spinal cord via the dorsal roots, and motor commands originate from the ventral part.
The stimulus, while not providing information on our current position, triggers a response. This response changes the body position and subsequently changes the stimulus.
Fictive Locomotion Experiment
This experiment was conducted to check the veracity of the chain of reflexes hypothesis.
The spinal cord was deprived of stimulation through three procedures:
- Separating the spinal cord from the brain (eliminating visual, balance, and auditory information).
- Cutting the dorsal roots to eliminate proprioceptive input.
- Paralyzing the muscles (which send and perform information) using substances like curare.
What Role Does the Brain Play?
3. Development of the Action of Walking
The development involves the maturation of motor centers that are able to inhibit or modify neonatal reflexes.
Neonatal reflexes are categorized as: Temporary or Permanent.