Does postural chain mobility influence muscular control in sitting ramp pushes?

Area of Science:

• Biomechanics and Motor Control
• Human Physiology

Background:

• Voluntary movement requires balance control, involving a postural chain for stabilization and a focal chain for movement.
• Understanding the interplay between postural mobility and motor execution is crucial for efficient movement.

Purpose of the Study:

• To investigate how reduced ischio-femoral contact (increased postural mobility) influences force production and muscle activation during isometric transient efforts.
• To explore the relationship between postural chain mobility, anticipatory postural adjustments (APAs), and posturo-kinetic capacity (PKC).

Main Methods:

• Seven adults performed maximal isometric pushes in sitting positions with full (100 BP) and reduced (30 BP) ischio-femoral contact.
• Recorded surface EMGs of 14 muscles, reaction forces, center of pressure displacement, and iliac crest acceleration.
• Analyzed force output, muscle activation patterns (EMG), and kinematic data.

Main Results:

• Reduced ischio-femoral contact enhanced push force and its rate of rise, indicating greater balance perturbation.
• Increased reaction forces and backward center of pressure displacement (pelvis rotation) were observed with reduced contact.
• Postural and focal muscles exhibited phasic EMG activity, with a distal-to-proximal recruitment order and anticipatory postural adjustments (APAs).
• Reduced contact increased APA amplitude and postural muscle activation levels, suggesting adaptation of the motor program to postural requirements.

Conclusions:

• Greater postural chain mobility facilitates enhanced dynamic counter-perturbations, termed posturo-kinetic capacity (PKC), enabling greater push force production.
• Postural control involves adapting motor programs based on postural requirements rather than altering strategies.
• Postural chain mobility is a key task parameter influencing motor control and performance.