Validity and reliability of the designed attachments for measuring trunk rotators torques using Biodex dynamometer in patient with chronic low back pain

Due to the trunk muscle weakness after chronic low back pain (CLBP), the evaluation of their function is an important part of rehabilitation protocols for CLBP. Therefore, providing the appropriate tools to measure trunk rotation torque is important. This study has been designed to evaluate the reliability and validity of the attached instruments to Biodex 4Pro for the measuring of isometric and isokinetic torque of trunk rotator muscles. 17 patients with CLBP and 17 healthy subjects (aged and sex matched) participated in the study. The isometric and isokinetic torques of trunk rotator muscles to the left and right were evaluated in 3 sessions with 7 days interval by 2 different examiners. The Persian version of disability Oswestry questionnaire was used to evaluate the validity of instrument. The findings showed that isokinetic and isometric torque of trunk rotator muscles are significantly lower in patients with CLBP than healthy subjects (P=0.013). The findings also indicate a good inter-tester reliability (r=0.62 to 0.82, P<0.01) and intra-tester reliability (r=0.53 to 0.84, P<0.01) of designed attached instrument. Intraclass correlation coefficient calculation between the disability score and trunk rotator muscle torque data from CLBP patients showed a high degree of reverse correlation (ICC= -0.596 to -0.812, P<0.01). The results of present study indicated that the attached instrument has a good validity and reliability to measure trunk rotator muscle torque in patients with CLBP. According to these findings, it is advisable to use of the designed device to evaluate the change of trunk rotator muscle torque after applying the treatment protocols for CLBP patients.