The determination of the validity of an application-based knee-training device.

The goals of knee rehabilitation are to improve range of motion and muscle status. The aim of the study was to investigate accuracy and reproducibility of a newly designed knee-training device (KT) under standardized laboratory conditions. Two application-based software programs, one to measure maximum force and the other intended to improve users' coordination were developed to be used on a tablet during exercises, wirelessly connected to KT placed under the popliteal fossa. KT was loaded for 20 intervals of 15 seconds (s) ranging between 0-350 Newton (N) each. The interval of times was chosen to be enough to take right measurement for accurate results. In addition, a 300-s continuous measurement was undertaken. The pressure readings were developed through a servo-hydraulic system and used as reference values. KT results were compared with the reference values to assess its accuracy. In addition, KT was tested on a force-measuring platform in a close to reality measurement. Based on Bland-Altman plots, the mean difference between KT and material testing machine was -0.63 N (0.4%), between KT and force-measuring platform was -0.11 N (0.7%), which proves the accuracy of its result. Laboratory experiments confirm that KT delivers precise and reproducible values, which provide base for clinical trials.