Effect of One-side-shoulder Bag Holding with Different Weights on Center of Gravity Shaking during a Standing Posture in Young Women

Center of gravity shaking (CGS) changes constantly during a standing posture and its variation increases depending on the disturbance stimulus. One-side-shoulder bag (OSB) holding with a heavy weight makes the standing posture unstable because it imposes burden on one side of the shoulder and/or lower back. It is assumed that the effect of OSB on CGS differs by bag weight and the habitual and non-habitual use of one shoulder. This study aimed to examine the effect of different weights and holding shoulders on CGS during OSB in a standing posture in 30 healthy young women aged 21-24 years. The experimental conditions were relative weight loads (0% [non-bag holding], 5%, 10%, and 15% of body mass [BM]) and bag holding shoulder (habitual and non-habitual). The participants maintained a Romberg posture (standing posture with feet closed) with eyes open for 1 minute on the measurement equipment in the above-mentioned eight conditions. The x-axis, y-axis, and total trajectory lengths and outer peripheral area were transmitted to a computer at a sampling rate of 20 Hz. The measurement order was randomized for the different weight loads and holding shoulders. Two measurements were obtained for each condition with a 1-min rest between measurements. The two measurements were then averaged. A two-way analysis of variance (ANOVA) showed that the x-axis, y-axis, and total trajectory lengths were significantly higher for weight loads of 10% BM and above. The outer peripheral area value was significantly lower for the habitual holding shoulder. The 10% and 15% BM weights had significantly higher outer peripheral area values compared with the 0% BM weight, and the 15% BM weight had significantly higher outer peripheral area values compared with the 5% and 10% BM weights. The x-axis, y-axis, and total trajectory lengths and outer peripheral area become greater as bag weight increases over 10% BM. OSB holding leads to a larger outer peripheral area in the non-habitual holding shoulder compared with the habitual holding shoulder in young women.