Prolonged standing (PS) is a common activity that is becoming more recommended in the work place. However, there's a strong association between PS and low back pain (LBP) with up to 81% of individuals reporting LBP after 2 hours or less on their feet. There is also a noted sex difference with this LBP development during PS, with women experiencing LBP with a higher frequency than men, while men report higher pain levels of LBP than women. The specific factors involved, and sex related

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... s are not fully understood. One potential factor may be bilateral asymmetries in posture. The goal of this study was to examine the effect of PS on bilateral weight-bearing, ground reaction force (GRF) control (i.e., center of pressure (CoP)) and core muscle activation within healthy young adult men and women during quiet stance (QS). Twenty-four healthy, pain-free subjects (12 men, 12 women) voluntarily participated in the study (age = 22.3 ± 2.4 years, height = 1.70 ± 0.09 m, mass = 69.89 ± 11.31 kg, BMI = 24.1 ± 2.5 kg/m 2 [mean ± SD]). Subjects performed two 60 second QS trials (pre-PS & post-PS) separated by one 30 minute free standing trial while bilateral GRFs under each foot and surface electromyography (sEMG) of each lumbar erector spinae (ES), gluteus medius (GM), internal obliquus (IO), and external obliquus (EO) were measured. Muscle activity was normalized to a submaximal reference contraction (%ref). Sway, maximum velocity (maxV), and path length (PL) were calculated from the CoP for both the dominant (D) and non-dominant (ND) foot, as well as net combined values. All CoPs were calculated in both the anterior-posterior (AP) and mediallateral (ML) directions, and were normalized to standing height (%height). Weight-bearing v ACKNOWLEDGEMENTS