Validity and reliability of measurements taken by the Peak 5 motion analysis system

Many new measurement tools are becoming available for physiotherapists; however, there is often a lack of data to support their validity and reliability. This study attempts to address this issue with respect to the Peak 5 video analysis system. Five experiments were conducted. Experiment A investigated the validity of static angular measurements by filming a universal goniometer. A high level of agreement was recorded with a mean difference between the two instruments of 0.2 degree. Experiment B investigated the validity of angular joint velocity by filming a Biodex isokinetic dynamometer. A high level of agreement was recorded with a mean difference between the two instruments of 0.96 degree s-1. Experiment C investigated the reliability of reflective marker placements on the hip, knee and ankle on 17 healthy volunteers, in weight bearing on three separate days. Reliability was high with the 95% confidence interval (CI) for marker placement being 1.5 cm. Experiment D investigated the normal intrasubject variation of knee joint 'critical angle' and angular velocity measures over time, by filming 17 healthy volunteers performing an eccentric step test on three separate days. For 'critical angle' measures the standard deviation was 5.72 degrees and the 95% CI was +/- 11.44 degrees. For angular velocity measures the standard deviation was 8.51 degrees s-1 and the 95% CI was +/- 17.02 degrees s-1. Experiment E repeated analysis of the reflective marker placement (mean standard deviation 0.6 cm), the 'critical angle' (mean standard deviation 1.32 degrees) and the angular velocity (mean standard deviation 1.29 degrees s-1 showed high consistency, when analysing three pieces of film three times. Data generated in this study suggest that the Peak 5 provides valid angular and angular velocity data when compared to other measuring devices. Reliable data are produced when filming healthy volunteers performing an eccentric step test. These data will be used in the next stage of the project investigating Anterior Knee Pain Patients.