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Effects of different tables heights on upper arms posture, discomfort and weight bearing on table surface during notebook use

Grant number: 13/16891-1
Support Opportunities:Scholarships in Brazil - Scientific Initiation
Effective date (Start): October 01, 2013
Effective date (End): September 30, 2014
Field of knowledge:Health Sciences - Physiotherapy and Occupational Therapy
Principal Investigator:Cristiane Shinohara Moriguchi de Castro
Grantee:Cecilia Capriogli Oliveira
Host Institution: Centro de Ciências Biológicas e da Saúde (CCBS). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil

Abstract

Notebook use has increased worldwide and is the main choice among university students. This fact could lead to the increase of musculoskeletal symptom reports by this population since they use computers for long periods and at inadequate ergonomic conditions. Forearm support provided by the desk to allow the upper arms weight-bearing is one of the recommendations by ergonomics guidelines for musculoskeletal disorders prevention during notebook use. However, ergonomics guidelines, in general, describe ergonomics recommendations in topics and do not show the interference between the recommendations. In this sense, implementing the forearm support as an ergonomics intervention without considering the table height could interfere with the intervention results, but this issue is not treated. Thus, the assessment of upper arms weight-bearing at different table heights will allow checking if the table height could interfere in the forearm weight-bearing. Besides, this study will quantify the upper arms weight-bearing above the table, which is a variable not frequently assessed by other studies. Therefore, the object of the present study is to evaluate upper arms weight-bearing above the table, neck (flexion/extension), and upper arms (upper arms elevation) posture and discomfort during typing tasks using the notebook at different table heights: recommended table height and elevated table height. For this purpose, 24 healthy university students (12 males and 12 females) who use notebooks will be evaluated (this sample was determined based on sample calculation considering pilot study results). The participants will be evaluated regarding anthropometric characteristics at sitting posture, which will allow to adequate the table and chair to each participant. The task will consist of typing on Microsoft Word for 8 minutes using a notebook at the table with recommended height and at the table with elevated height. The tasks order will be random. Dependent variables will be: upper arms weight-bearing evaluated by means of load cells (instrumented table); neck flexion/extension, upper arms elevation evaluated by means of inclinometry; and perceived discomfort evaluated by CR10 Borg Scale (Borg, 1998). Data will be processed using MatLab (versão 7.01, MathWorks Inc, Natick, USA). Kinematic and upper arms weight-bearing data will be filtered by 2nd order Butterworth filter and the cutoff frequency will be determined by residual analysis. In the next step, data will be reduced by the amplitude probability distribution function method (APDF) to estimate 10th, 50th and 90th percentiles of postures and weight-bearing. The upper arms weight bearing will be evaluated by the percentage of the upper arms weight, measured during the sitting posture, and upper arms relaxed resting above the load cells (instrumented table). The distribution of dependent variables (weight-bearing, posture, and discomfort) will be tested by the Shapiro-Wilk test. If data present normally distributed, T Student Test for repeated measures will be used to compare the two conditions (table at recommended height and at elevated height). The results of the present study will allow verifying the effect of different table heights on weight load-bearing, posture, and discomfort, which may reinforce the importance to consider the relationship between the ergonomics recommendations for effective results. Thus, the present study will provide evidence to ergonomics guidelines regarding the prevention of musculoskeletal disorders among notebook users.(AU)

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