Frequency Analyses of Postural Sway during Prolonged Sitting on a Large Gymnastics Ball and Stool

Abstract

Selected schools in Slovenia have launched an initiative to replace school chairs with large gymnastics balls (LGBs) in order to improve children’s posture. The rational given was that LGB saffect posture in a way that is beneficial to the body because they mimic the frequencies of body movement during walking. To identify the influence of seating furniture on the frequency of postural sway, the postural dynamics of eight school children were studied. A comparison was made of their posture while they were sitting on a stool and on a LGB, each for 30 minutes. The lumbar lordosis (LL) and pelvicinclination (PI) angles were both studied. They were measured from the sagittal plane with a video measurement system (3 fps). From the time pattern of each angle, calculations were made to determine the frequency spectrum median and distribution of power in frequency spectra at four intervals: 1) 0.01–0.05 s−1, 2) 0.05–0.1 s−1, 3) 0.1–0.33 s−1, and 4) 0.33–0.6 s−1. It was determined that the median for LL is at a higher frequency on a LGB (LGB = 0.17 s−1 0.03 s−1, stool = 0.14 s−1 0.03 s−1, p < 0.05), but no differences were found in PI. Sitting on a LGB had more power in the third interval with a typical sway period of 5 s (p < 0.05), whereas sitting on as tool had more power in the first interval with a typical sway period of 33 s (p < 0.05). Sitting on a LGB influences the upper body dynamics and promotes a sitting posture with a period of sway that is closer to the sway pattern experienced during walking as compared to sitting on a stool.