Adapted protocol of rate of force development and relaxation scaling factor for neuromuscular assessment in patients with knee osteoarthritis

Background: The linear relationship between muscle torque and rate of torque rise/relaxation during rapid muscle contractions has been recently introduced as a novel measure of muscle quickness, termed rate of torque development/relaxation scaling factor (RTDSF/RTR-SF). Because the standard assessment protocol includes potentially painful muscle contractions, the first purpose of this study was to validate an adapted RTD-SF/RTR-SF protocol for knee extensor muscles that utilizes lower submaximal intensities and can be used in knee osteoarthritis patients. Methods: A cross-sectional study was performed on a group of healthy controls (n = 24) who underwent the standard RTD-SF/RTR-SF protocol (20–80% of maximum) and the knee osteoarthritis group (n = 24) who underwent the adapted protocol (20–60% of maximum). We calculated the RTD-SF, RTR-SF and the linearity (r 2 ) for both relationships, based on both protocols in controls. Results: The validity of the adapted protocol was acceptable (intraclass correlation coefficient = 0.77–0.93), with low within-participant variation (coefficient of variability