RESUMEN
Bradykinesia is associated with reduced quality of life and medication non-compliance, and it may be a prodrome for schizophrenia. Therefore, screening/monitoring for subtle bradykinesia is of clinical and scientific importance. This study investigated the validity and reliability of such an instrument. Included were 70 patients with psychotic disorders. Inertial sensors captured mean cycle duration, amplitude and velocity of four movement tasks: walking, elbow flexion/extension, forearm pronation/supination and leg agility. The concurrent validity with the Unified Parkinson's Disease Rating Scale (UPDRS) bradykinesia subscale was determined using regression analysis. Reliability was investigated with the intra-class correlation coefficient. The duration, amplitude and velocities of the four tasks measured by the instrument explained 67% of the variance on the UPDRS bradykinesia subscale. The instrument test-retest reliability was high. The instrument investigated in this study is a valid and reliable alternative to observer-rated scales. It is an ideal tool for monitoring bradykinesia as it requires little training and experience to achieve reliable results.