Influence of Reflected Marker Size in Accuracy of Motion Analysis

Background: Three dimensional motion analysis systems are the most advanced tools in the field of movement analysis, in our time many factors influence its accuracy such as marker size however there is little researcher was paid attention to the size of marker as a factor in determining the accuracy of results. The purpose of this study was to investigate the influence of different reflected marker size in accuracy of motion analysis. Subjects: 30 normal healthy subjects their ages ranged from 18 to 24 years with a mean of 19±2.6 years. Design: test-retest, Three 120 Hertz infrared cameras used to capture the position and determine the value of the three co-ordinates of the markers in millimeter. Subject captured using the three different size of markers (3mm, 9mm, 24mm) then after one hour interval repeated capture was taken, then (x,y ,z) of every marker in first trial of capturing would added to the same coordinate of the same marker size then divided on number of trials to get the mean of both trial for each marker size. Method: three passive markers placed over the upper limb of definite size while the subjects were sitting on a chair, subject captured by the three different size for two times with one-hour interval then a mean for both trial of every marker size tacked. Data collected and analyzed using the interclass correlation co-efficient. Results: inter class correlation model used to determine interclass correlation co-efficient between every size of markers. Analysis of variance with repeated measurements test and Bonferroni post hoc analysis concluded that large marker has a good effect on accuracy of results p<0.05. Discussion: placement of different size of markers showed high accuracy of large markers due to the higher presentation of the marker in camera volume. Conclusion: It concluded that using of large marker has good results on accuracy of motion capturing.