Changes of lumbosacral joint compression force profile when walking caused by backpack loads

Area of Science:

• Biomechanics
• Spinal Health
• Ergonomics

Background:

• Backpack loads are a known risk factor for lower-back pain due to increased spinal mechanical stress.
• Understanding the precise effects on spinal joint forces is crucial for injury prevention.

Purpose of the Study:

• To evaluate how varying backpack loads affect the magnitude and timing of lumbosacral joint compression force during walking.
• To quantify the relationship between backpack load and spinal biomechanics.

Main Methods:

• Ten male adults walked with no load and with backpack loads (5-20% body weight).
• Motion analysis, force plates, and surface electromyography recorded movements, forces, and muscle activations.
• An integrated inverse dynamics and EMG-assisted optimization model predicted lumbosacral joint force profiles.

Main Results:

• Increasing backpack load disproportionately elevated the 10th, 50th, and 90th percentiles of lumbosacral joint compression force.
• No significant changes were observed in the timing of peak force incidences.
• Force profiles showed strong associations (Pearson correlation > 0.94) across different loading conditions.

Conclusions:

• Increased backpack load significantly alters lumbosacral joint compression force magnitude, likely due to combined gravitational and inertia effects.
• The observed changes in force profiles suggest a heightened risk for spinal structures with heavier loads.
• Findings underscore the importance of load management in preventing lower-back pain associated with backpack use.