Side-to-side weight-bearing asymmetry during standing and hip-carrying posture: a cohort study comparing parous and nulliparous females.

Author: Daniel Rollins                                                                                Supervisor: Nico Tanguy

Abstract: The purpose of this study was to determine whether parous females exhibit an increased side-to-side weight-bearing (WB) asymmetry during static upright posture and asymmetrical hip-carrying tasks. Seventy females (35 parous; 35 nulliparous) participated in the study. The study utilised an adjustable weight manikin, equivalent to the average weight of a female child at the age of 6 months (7.5kgs: Load 1) and 24 months (12kgs: Load 2), to be carried on the hip. A participant questionnaire provided data on demographics, incidence and location of pain distal to the Lumbar 1 (L1) vertebra.

Participants performed 3 standing trials for each load condition (Unloaded, Load 1 and Load 2) on identical sets of digital scales. Weight-bearing distribution (WBD; average inter-limb weight-bearing differences over 3 trials) were calculated and normalised for participant weight. 

Inter-group analysis: no significant differences in asymmetrical WBD were found between parous and nulliparous groups. However, 10% of the study population did exhibit a greater than expected WB asymmetry whilst load-carrying, of which 71% were from the parous group. 

Intra-group analysis: asymmetrical load-carrying significantly affects side-to-side WBD in both groups, with greater magnitudes of difference observed with heavier loads. 

WBD was not significantly affected by the incidence of pain, age, BMI, perception of postural change or breastfeeding. The incidence of pain was elevated in participants with increased age, BMI and who reported postural change since giving birth.

The findings of this study provide a basis for future research and to inform osteopaths, and manual therapists alike, of the effects that asymmetrical load-carrying has on posture and WBD. This may then serve to inform treatment plans so that improved patient management and outcomes may be achieved.