Intra-Rater, Inter-Rater and Test-Retest Reliability of an Instrumented Timed Up and Go (iTUG) Test in Patients with Parkinson's Disease

The Timed Up and Go test (TUG) is widely used to assess physical function in older adults and neurological populations, including Parkinson’s disease (PD). When combined with inertial sensors (instrumented TUG, iTUG), individual movement components and trunk kinematics can be analyzed, providing additional quantitative information. This study investigated intra-rater, inter-rater, and test–retest reliability of iTUG parameters in PD patients.

Twenty-eight PD patients aged 50 years or older performed the iTUG using a DynaPort Hybrid sensor worn at the lower back. Acceleration and angular velocity were recorded in three dimensions at 100 Hz. Patients completed five iTUG trials on two consecutive days. Intra-rater reliability was assessed using repeated measurements by the same rater on the same day, inter-rater reliability using different raters on the same day, and test–retest reliability using the same rater across days.

Results showed excellent reliability (ICC ≥ 0.90) for 15% of parameters and good reliability (ICC ≥ 0.70) for 49%. Moderate reliability (ICC 0.50–0.69) was found in 24% of parameters, while 14% showed poor to very poor reliability. Overall, total iTUG duration and turning durations demonstrated excellent to good reliability, whereas sub-phase durations and sit-to-stand and stand-to-sit kinematic parameters showed lower reliability.

In conclusion, several iTUG parameters exhibit sufficient reliability in PD patients, supporting their use for a more precise and quantitative assessment of mobility in clinical practice.