Ergonomics

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1. EXECUTIVE SUMMARY
The aim of this study is to investigate the isometric strength or MVC (maximum voluntary contraction) by measuring grip strength, arm strength, leg strength, torso strength and key pinch strength. So that each participant’s strength percentile values in the population for each strength category can be calculated and human biomechanical capabilities and relative variability in human capabilities can be understood by comparing the data collected. Also the effects of the factors, like grip span, wrist posture or using the dominant side, on each of the strength categories can be examined. 2. INTRODUCTION

Isometric strength is the force that a muscle group can exert without movement. Maximum Isometric strength is the maximum force that a muscle group can exert without movement. It is also called MVC (maximum voluntary contraction). Some of the widely used isometric strengths are: arm strength, shoulder strength, composite (leg) strength, back (torso) strength, grip strength and pinch strength. All of the strength categories are measured for the subjects excluding for the ones having health problems about their waist. These measurements are done by using Caldwell Protocol, which says that after a build-up time of about 2 seconds, the subject is required to maintain a steady state maximal exertion for at least 3 seconds and this (average) level is taken as the subject’s strength score. So that we can say that, in general, the isometric strength measurement procedure requires individuals to build-up their muscular exertion slowly over a 4-6 seconds period, without jerking, and maintain the peak exertion for about 3 seconds. This peak exertion (3 sec average) is the isometric strength of the individual. No external motivation should be provided. A break of at least 30 seconds should be provided between successive exertions if only a few measurements are to be made. It is necessary to increase the rest duration to 2 minutes if about 15 measurements are to be made in one test session. This additional rest is necessary to recover from fatigue generated due to the isometric exertion (Mital and Kumar, 1998). While measuring the strength categories, the effects of some factors like elbow angle, wrist posture, grip span and using dominant or non-dominant side are observed. The orientation of the arm influences human isometric strength exertion capability. As the arm orientation changes the mechanical advantage also changes, resulting in weaker or stronger strength exertions. Also the wrist orientation is critical in generating isometric torques with non-powered hand tools. Approximately 70% more torque is exerted when wrenches are in the horizontal position than when they are in vertical positions (Mital and Kumar, 1998). Therefore, by using some statistical techniques like ANOVA (Analysis of Variance), the significance of the factors that are mentioned before is tested. 3. OBJECTIVES

The main objective of this study is to investigate the isometric strength or MVC (maximum voluntary contraction) by measuring grip strength, arm strength, leg strength, torso strength and key pinch strength. So that each participant’s strength percentile values in the population for each strength category can be calculated and human biomechanical capabilities and relative variability in human capabilities can be understood by comparing the data collected. Also the effects of the factors, like grip span, wrist posture or using the dominant side, on each of the strength categories can be examined. 4. METHODS

The experimental task consisted of performing isometric handgrip, pinch grip and lifting contractions for the combinations of the levels of wrist posture, grip-span and by using the dominant or non-dominant side in a standing posture. The equipments used are handgrip dynamometer, pinch grip dynamometer and lift platform. Our lab group conducting this study consists of two female and a male student,...
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