Mediolateral postural stability when carrying asymmetric loads during stair negotiation

Area of Science:

• Biomechanics
• Human Movement Science
• Ergonomics

Background:

• Stair negotiation is a common daily activity that requires significant postural control.
• Carrying loads, especially unilaterally, can alter biomechanical demands and challenge postural stability.
• Understanding these challenges is crucial for preventing falls and optimizing movement strategies.

Purpose of the Study:

• To evaluate postural stability in the medial-lateral (ML) direction during stair negotiation while carrying unilateral and bilateral loads.
• To compare the effects of no load, bilateral load, and unilateral load on postural control during stair ascent and descent.

Main Methods:

• Twenty-four healthy young adults participated in the study.
• Participants ascended and descended a three-step staircase under three conditions: no load, 20% body mass (BM) bilateral load, and 20% BM unilateral load.
• A modified time-to-contact (TTC) method was used to quantify ML postural stability.

Main Results:

• Unilateral loads necessitated quicker postural adjustments during stair descent, indicated by lower minimum ML TTC and ML TTC percentage compared to bilateral loads and no load.
• Lower ML TTC and TTC percentage were observed during the loaded limb stance in stair descent.
• Postural control challenges differed between stair ascent and descent under loaded conditions.

Conclusions:

• Unilateral load carriage, particularly during stair descent, poses a significant risk to postural stability.
• The loaded leg during stair descent is a critical factor influencing stability.
• These findings underscore the importance of considering load distribution and movement direction for safe load carriage during stair negotiation.