en Physical Medecine& Rehabilitaion Physical Medecine& Rehabilitaion Original Research Original Research <p> <strong> Abstract </strong></p><p> <strong> Background: </strong>Postural instability has been identified as a potential precursor of </p><p>  falls in elderly subjects. Postural stability in quiet stance is commonly assessed with </p><p>  center of pressure (COP) measures. The purpose of this study was to determine testretest reliability and minimal detectable change (MDC) for the center of pressure </p><p>  (COP) measures in the elderly subjects. </p><p> <strong> Methods: </strong>Eighteen healthy elderly people over the age of 60 years participated in </p><p>  this study. For each subject the COP was recorded during quiet upright stance on different levels of postural difficulty (eyes open versus eyes closed, firm surface versus </p><p>  foam surface) and lean condition (forward and backward). All measurements were </p><p>  done on two sessions with 7 days interval. These indices: mean velocity, standard deviation of amplitude, standard deviation of velocity, phase plane parameter and area </p><p>  (95% confidence ellipse). Intraclass correlation coefficient (ICC), standard error of </p><p>  measurement (SEM) and coefficient of variation (CV) were used to quantify testretest </p><p>  reliability. The MDC for each measure was calculated to quantify intervention </p><p>  effects. </p><p> <strong> Results: </strong>In general, test-retest reliability of COP measures in the elder subjects </p><p>  was increased whenever postural difficulty of task increased in quiet standing. In </p><p>  standing conditions, mean velocity and phase plane parameter were the most sensitive </p><p>  and the most reliable measures. The lean range was the most sensitive and the </p><p>  most reliable measure, in the lean conditions. </p><p> <strong> Conclusion: </strong>Center of pressure measures in the quiet standing especially in difficult </p><p>  postural conditions demonstrated high sensitivity in the older subjects. These results </p><p>  may be useful in quantification and assessment of balance performance and </p><p>  treatment efficacy. </p><p>  </p> Reliability, Minimal Detectable Change, Center of Pressure, balance,Elder People 224 232 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-1-95&slc_lang=en&sid=1 Reza Salehi Salehi200@yahoo.com 20031947532846001889 20031947532846001889 Yes School of Rehabilitation Science, Iran University of Medical Science Ismaeil Ebrahimi-Takamjani 20031947532846001890 20031947532846001890 No Iran University of Medical Science, Tehran, Iran. Ali Esteki 20031947532846001891 20031947532846001891 No Shahid beheshti University of Medical Science, Tehran, Iran. Nader Maroufi 20031947532846001892 20031947532846001892 No Iran University of Medical Science, Tehran, Iran. Mohammad Parnianpour 20031947532846001893 20031947532846001893 No Sharif industrial University, Tehran, Iran.