Reliability Of Single Leg Landing On A Portable Force Platform

Abstract

Impact forces at landing are related to valgus moments at the knee and potential ACL injury risk. Reliable tests that are portable and applicable to large scale screening are important to identify high risk individuals in order to target them for appropriate interventions. PURPOSE The purpose of this study was to investigate within session reliability of measures of single leg landing in a large group of female athletes. The hypothesis tested was that within session measures of force and center of pressure (COP) would be reliable during single leg landing. METHODS 45 high school and collegiate soccer players volunteered participation. Each performed a 50cm single leg hop and were instructed to balance for 10 seconds after the landing. A portable force platform (AccuPower, AMTI) was used with force and center of pressure (COP) data. Balance during the trial was assessed by calculating the standard deviation of each variable (COPML, COPAP, FML, FAP, FV). The range of COP excursion (ML and AP) was also calculated during the balance portion of each trial. Stability algorithms utilized sequential estimation during the initial 3 seconds after impact (Colby, 1999). The time of stability (medial/lateral (ML), anterior/posterior (AP) and vertical force (V)) derived from sequential estimation has been previously shown to be reliable when collecting 10 trials. Intraclass correlation coefficients (ICC[3, k]) were performed in SPSS for each variable. RESULTS Maximum vertical ground reaction force had high reliability on both the right (r = 0.823) and left side (r = 0.877). The maximum vertical ground reaction force for the three trials on the right side was 2.40BW, 2.41BW and 2.40BW, respectively. The average (right and left side) reliability for the standard deviation was: COPML (r = 0.831), COPAP(r = 0.651), FML(r = 0.824), FAP(r = 0.714) and FV(r = 0.741). Average COP medial/lateral excursion had a reliability of r = 0.736 and anterior/posterior excursion was r = 0.607. The stability time measurement that had an ICC over 0.6 was calculating the vertical force with sequential estimation (right, r = 0.787 and left r = 0.767). CONCLUSIONS Maximum vertical force and the standard deviation and excursion measures had high reliability during three trials in female athletes. Calculation of stability time from medial/lateral and anterior/posterior force was less reliable. Calculation of a stability time from sequential estimation based on the vertical component was improved compared to the use of M/L and A/P.