Trunk stiffness decreases and trunk damping increases with experimental low back pain

Area of Science:

• Biomechanics
• Pain Research
• Human Movement Science

Background:

• Movement adaptations are thought to protect painful areas.
• Previous studies show increased trunk stiffness and decreased damping in recurrent low back pain (LBP).
• Trunk dynamics during acute LBP remain understudied.

Purpose of the Study:

• To investigate trunk dynamical properties during experimentally induced acute low back pain (LBP).
• To compare trunk stiffness and damping before, during, and after an acute painful stimulus.
• To understand protective movement adaptations in response to acute noxious input.

Main Methods:

• Experimentally induced acute LBP using hypertonic saline injection.
• Trunk force perturbation paradigm with a mass-spring-damper model.
• Estimation of effective trunk stiffness (K) and damping (B) in 14 healthy males.

Main Results:

• Trunk stiffness (K) decreased during acute pain compared to before and after.
• Trunk damping (B) increased during acute pain compared to before and after.
• Adaptations involved controlling trunk velocity rather than displacement.

Conclusions:

• Acute low back pain (LBP) induces a decrease in trunk stiffness and an increase in damping.
• These findings contrast with adaptations observed in recurrent LBP.
• The system prioritizes velocity control over displacement control during acute noxious stimuli.