What is slumped sitting? A kinematic and electromyographical evaluation

Area of Science:

• Biomechanics
• Ergonomics
• Spinal Physiology

Background:

• Slumped sitting is a common reference posture, yet its precise definition and regional spinal characteristics remain unclear.
• Understanding slumped sitting is crucial for comparing its effects with upright postures in various populations.
• The passive nature of slumped sitting needs comparison with active-flexion postures.

Purpose of the Study:

• To clearly define the regional spinal and pelvic posture during slumped sitting.
• To compare the passive slumped sitting posture with active seated maximum forward flexion.
• To analyze electromyographical (EMG) activity in key back muscles during these postures.

Main Methods:

• Collected kinematic and electromyographical (EMG) data from 12 male participants.
• Measured spine angles in four regions (three thoracic, one lumbar) and pelvis during slumped sitting and maximal forward flexion.
• Normalized EMG data to a percentage of maximum voluntary contraction (%MVC).

Main Results:

• Slumped sitting characterized by 10° posterior pelvic tilt and significant thoracic flexion (mid: 90%SIT-FF, lower: 81%SIT-FF).
• Upper-thoracic (51%SIT-FF) and lumbar (43%SIT-FF) regions showed mid-range flexion.
• A significant 3%MVC reduction in lower-thoracic erector spinae activation was observed from upright to slumped sitting.

Conclusions:

• Slumped sitting involves distinct regional spinal configurations, differing significantly from active flexion.
• Normalization methods (seated vs. standing) impact the interpretation of spinal posture data.
• Specific muscle activation changes, like reduced erector spinae activity, highlight the passive nature of slumped sitting.