Low back joint loading and kinematics during standing and unsupported sitting

Area of Science:

• Biomechanics
• Ergonomics
• Spinal Health

Background:

• Prolonged sitting is common in many occupations.
• Understanding spinal loads and muscle activity during sitting is crucial for ergonomic design.
• Current knowledge gaps exist regarding the comparative biomechanical effects of static vs. dynamic sitting postures.

Purpose of the Study:

• To analyze lumbar spine kinematics, joint loads, and trunk muscle activation during a 2-hour sitting period.
• To compare biomechanical parameters between prolonged sitting and standing.
• To inform the design of work environments that allow for posture variation.

Main Methods:

• Utilized a detailed anatomical biomechanical model with 104 muscles, ligaments, and discs.
• Incorporated biological signals of spine posture and electromyograms (EMG) from subjects.
• Compared spinal loads and muscle activation patterns between sitting and standing conditions.

Main Results:

• Sitting resulted in significantly higher low back compressive loads (1698 N) compared to standing (1076 N).
• Standing induced distinct spine postures compared to sitting, with no overlap in averaged flexion postures.
• Erector spinae muscles showed increased activation during sitting, with no significant differences between static and dynamic sitting strategies.

Conclusions:

• Standing provides a biomechanical respite from sitting due to reduced passive tissue forces.
• Neither prolonged standing nor sitting offers significant dynamic movement or substantial relief in muscular activation or loading.
• Ergonomic interventions should focus on facilitating posture variation to mitigate constant loading.