Baumgartner, Daniel

Kool, Jan

Kuster, Roman

Oetiker, Sarah

ZHAW digitalcollection

Muscular Activity while Sitting on a Novel Dynamic Office ChairMethodTen office workers laterally flexed their spine in self-selected comfortable range during a standardized reading task.Maximum spine-flexion and thorax-inclination and -translation were measured with infrared cameras during dynamicsitting for five minutes. Muscular activity of back muscles (left and right longissimus (L-/R-LONG), left iliocostalis (L-ILIO),right multifidus (R-MULT)) and thigh muscles (right vastus medialis (R-VASTM) and lateralis (R-VASTL)) were recorded bysurface EMG while dynamic and static sitting and expressed as % of maximum EMG activity during gait.BackgroundLong-lasting static sitting significantly increases the risk of all-cause-mortality(1&2). Even low back pain is discussed as negative healthconsequence of prolonged static sitting periods(3) (>4 hours a day). Science therefore generally recommends that continuous posturalchanges should be supported by the chair to reduce negative health effects. Since no dynamic office chair was identified thatsignificantly changes trunk muscle activity (4), a novel dynamic office chair was developed. The additional degree of freedom of thechair is enabled by a circular motion of the seat in the frontal plane around a center of rotation within the chair user’s body.ResultsSubjects laterally flexed their spine 6.1±1.5° while the thorax was moved 0.9±0.7° and 7±5mm, respectively. Muscularactivity of the back muscles while dynamic sitting varied between 21±7% to 71±25% compared to 21±11% to 100% inwalking (see tab 1), while constant mean activity in static sitting was between 25±8% and 50±18%. Thigh muscle activityvaried between 9±2% to 22±24% compared to walking (9±2% to 100%).Muscular activity of the back was lower for dynamic compared to static sitting while 17±19% up to 47±25% of the time,and lower muscular activity of the leg was found between 9±2% and 22±24% of the time.DiscussionOn the novel office chair, subjects are able to laterally flex their spine during a reading task although the thoraxremains stable. The low thigh activity indicates that the movement is performed mainly by the upper bodymuscles. The activity variation of back muscles while normal dynamic sitting is comparable to walking, butsubstantial smaller maximum values of about -30 to -60% were observed.ConclusionAccording to current literature(4), the novel office chair is the first scientifically investigated chair thatsignificantly change trunk muscle activity, applying not only additional load, but also cyclic relief of the relevantback muscles during 17 to 47% of dynamic sitting time.Kuster R P (1+2), Oetiker S (2), Baumgartner D (1), and Kool J (2)(1) ZHAW Zurich University of Applied Sciences, Institute of Mechanical Systems(2) ZHAW Zurich University of Applied Sciences, Institute of Physiotherapymuscle min dynamic sitting max dynamic sitting time dyn. < stat. sitting static sitting min walkingleft longissimus 24.7±12.2 (7.9-51.6) 46±15.2 (26.4-71.4) 45.1±25.8 (2.5-83.5) 32.7±14.5 (16.2-60.3) 20.9±10.6 (6.8-39.2)right longissimus 27.7±9.4 (16.1-41.5) 51.5±13.2 (35.8-69.5) 47.1±25.1 (10.5-78) 37.2±9.1 (25.2-47.9) 37.5±23.6 (11.7-86.1)left iliocostalis 47.0±13.4 (28.4-65.7) 70.6±25.4 (44.1-112.5) 16.9±19.4 (0-46.0) 49.9±17.8 (28.7-82.0) 40.4±15.8 (10.2-58.3)right multifidus 21.3±7.4 (8.6-32.3) 39.4±12.3 (16.1-54.8) 29.9±27.4 (0-89.5) 25.2±8.4 (13.7-39.1) 23.8±10.8 (8.8-44.2)right vastus medialis 8.8±2.3 (6.5-11.2) 10.7±3.6 (7.7-15.3) 31.8±17.8 (7.0-47.0) 9.3±2.6 (6.7-12.2) 8.9±2.3 (6.2-11.8)right vastus lateralis 15.4±14.1 (5.7-36.1) 21.8±24.1 (6.8-57.6) 52.5±31.1 (6.0-70.0) 17.4±17.3 (6.1-43.1) 16.0±14.1 (6.9-40.7)Fig 1: Novel dynamic office chairFor comparison to static sitting, the seat was locked in the middle position.Fig 2: Laboratory DataData of the motion to the left (1-100) and right (101-200) are time-normalized. In the first row, angular orientation of the pelvis and thethorax is shown. In row 2 to 4, muscular activity are shown in % ofmaximum activity measured while walking. Thick line indicates themean, thin line above and below standard deviation (sd). Straightshaded line in violet reflects muscular activity during static sitting(mean and sd). Muscular activity of individual subjects are plotted inthe background.Tab 1: Muscular activity while dynamic and static sitting and walking in self-selected lateral flexion of the spineMuscular activity in % of walking of 4 back and 2 thigh muscles. Data of dynamic sitting are indicated at minimum and maximum activity (mean ± standarddeviation and full range in brackets), data of static sitting at mean activity, data of walking at minimum activity (maximum activity corresponds to 100%). Time inwhich the muscular activity in dynamic sitting was below muscular activity of static sitting (time dyn. < stat. sitting) is expressed as % of sitting time.References:1 Katzmarzyk et al. 2009, Med Sci Sports Exerc2 Dunstan et al. 2012, Diabetes Res Clin Pract3 Lis et al. 2007, Eur Spine J4 O’Sullivan et al. 2013, Appl Ergon20050 100 150010°0°-10°20050 100 15002.5°-2.5°pelvis thorax60402020050 100 150060402020050 100 1500L-LONG R-LONG1020050 100 1500402020050 100 1500R-VASTM R-VASTL100806020050 100 1500R-MULTL-ILIO402020050 100 1500Industrial partner:

Muscular activity while sitting on a novel dynamic office chair

ZHAW Zürcher Hochschule für Angewandte Wissenschaften

https://digitalcollection.zhaw.ch/bitstream/11475/10177/1/R145_Muscular_Actvity_while_Sitting.pdf

Muscular activity while sitting on a novel dynamic office chair

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