Active trunk stiffness during voluntary isometric flexion and extension exertions

Area of Science:

• Biomechanics of human movement
• Spinal stability and control
• Neuromuscular function

Background:

• Torso musculature elastic stiffness is key for spinal stabilization.
• Trunk stiffness during exertions offers insights into stabilizing control for tasks like pushing and pulling.

Purpose of the Study:

• To compare muscle activity and trunk stiffness during isometric trunk flexion and extension exertions.
• To investigate the neuromuscular control strategies for spinal stability.

Main Methods:

• Twelve participants performed isometric trunk flexion and extension against external loads.
• Trunk stiffness, damping, and mass were calculated from force disturbances and trunk movements.
• Muscle activity was recorded from key trunk muscles, including rectus abdominus, external oblique, and paraspinals.

Main Results:

• Greater antagonistic muscle recruitment was observed during flexion compared to extension exertions.
• Trunk stiffness was significantly higher during flexion exertions, even with similar applied forces.
• Trunk stiffness increased proportionally with exertion effort.

Conclusions:

• Flexion exertions necessitate greater antagonistic co-contraction for spinal stability than extension exertions.
• Differences in active trunk stiffness are linked to antagonistic muscle activity during flexion.
• Flexion tasks involve unique neuromuscular control, impacting spinal loads and requiring consideration of muscle recruitment patterns.