Impact of asymmetrical load magnitude and location on postural sway metrics in healthy young adults.

BACKGROUND

Asymmetrical load carriage is a common component of daily activities. Carrying a backpack, handbag, or groceries on one side for example alters the center of mass of the system and may challenge postural stability. Such asymmetrical demands on postural control may be a meaningful stressor to evaluate and address during clinical management.

OBJECTIVE

To determine the influence of lateral asymmetrical load on postural metrics, whether greater loads produce larger responses, and whether location of the load affects the response.

METHODS

Twenty-four healthy young adults (21.13 ± 1.48 years) participated in this repeated-measures study during November 2025. Participants completed five standing conditions including no load, handheld as well as shoulder loads at 15% and 20% body mass using the same backpack. Postural metrics were assessed using a force plate. Outcome measures included average mediolateral center of pressure location (COP X), average anteroposterior center of pressure location (COP Y), 95% ellipse area of postural sway, and total path length. Repeated measures analyses of variance with planned contrasts were performed to evaluate differences among conditions.

RESULTS

Loaded conditions demonstrated greater mediolateral shift in COP X (toward the side of load), greater 95% ellipse sway area, and greater path length compared with the no load condition. Greater magnitude loading (e.g. 20% vs. 15%) amplified both COP X and path length. Hand loading increased mediolateral shift in COP X more than shoulder loading whereas shoulder loading increased 95% sway area more than the hand. Load location did not affect path length. Lateral loading had no statistically significant effect on COP Y.

CONCLUSIONS

Both load magnitude and load location influence postural control metrics during asymmetrical load carriage. Clinicians may use this information to guide patients toward safer load carrying strategies when attempting to reduce postural instability and musculoskeletal strain.