One motion, different strategies: Intra-individual spinal movement variability during a repeated flexion task

Area of Science:

• Biomechanics
• Spinal Kinematics
• Human Movement Analysis

Background:

• Spinal movement variability is a normal aspect of repetitive motions.
• Hypothesized differences in variability exist between individuals with and without low back pain.
• Lack of normative intra-individual variability data hinders the assessment of abnormal spinal motion.

Purpose of the Study:

• To assess intra-individual variability in spinal flexion movements in healthy individuals.
• To establish normative values for spinal movement variability.
• To identify common sources of spinal movement variability.

Main Methods:

• Utilized motion capture cameras and a 19x3 retroreflective marker matrix (S1-C7 levels).
• Assessed intra-individual variability of 3 blocks of 10 repeated spinal flexion movements.
• Employed principal components analysis (PCA), single component reconstruction, and coefficient of variation (CV).

Main Results:

• Lumbar spine exhibited lower CV (1.9-25.3%) compared to the thoracic spine (7.9-30.1%).
• 2-5 principal components were required to explain ≥80% of total movement variance per participant.
• Magnitude changes, waveform differences, and phase shifts were common sources of variability, often linked to CV > 10%.

Conclusions:

• Healthy individuals demonstrate significant intra-individual variability in spinal movement.
• PCA and single component reconstruction effectively interpret the sources of this variability.
• Findings provide a foundation for understanding abnormal spinal motion in clinical populations.