Forward and backward axial synergies in man

Area of Science:

• Biomechanics
• Human Movement Analysis
• Motor Control

Background:

• Understanding the biomechanics of human trunk movement is crucial for analyzing posture and locomotion.
• Previous research has explored trunk movements, but detailed analysis of muscle activation patterns and segment coordination during forward and backward bending is ongoing.

Purpose of the Study:

• To analyze upper trunk and head movements in human subjects.
• To investigate the coordination between trunk, hip, and knee movements.
• To examine electromyographic (EMG) activity of flexor and extensor muscles during different movement speeds and directions.

Main Methods:

• Subjects performed forward and backward upper trunk movements while standing on a force platform.
• Kinematic data were captured using the EL.I.TE. system.
• Electromyography (EMG) was used to record muscle activity of key flexor and extensor muscles.

Main Results:

• Trunk movements were accompanied by counter-movements of the hip and knees, stabilizing the center of gravity projection.
• Fast movements exhibited simultaneous displacement of body segments, indicating feedforward control.
• Slow movements showed sequential, cranio-caudal segment displacement.
• Forward bending involved a distinct prime mover (Rectus Abdominis) and coordinated postural muscles (Vastus Medialis, Tibialis Anterior, Soleus).
• Backward bending showed simultaneous activation of the prime mover (Erector Spinae) and postural leg muscles (Hamstrings, Soleus).
• Forward bending included an initial forward knee displacement, potentially aiding movement or muscle pre-stretching.

Conclusions:

• Human trunk movements are controlled by sophisticated coordination strategies involving multiple body segments.
• Both feedforward and feedback mechanisms contribute to motor control during trunk movements, with speed and direction influencing the strategy.
• The observed knee displacement during fast forward bending may serve a functional role in facilitating the movement or enhancing muscle performance.