Motor abnormalities are highly prevalent among patients with schizophrenia spectrum disorders. Very likely, motor control processes, such as dexterity and grip force (GF), are impaired in schizophrenia. We aimed to explore associations between various motor abnormalities and motor control processes and to investigate whether specific motor abnormalities predict the performance of fine motor movements and GF. Our analyses included 198 patients with schizophrenia spectrum disorders. We applied well-established standardized motor rating scales to assess five different motor abnormalities: psychomotor slowing (PS), neurological soft signs (NSS), parkinsonism, catatonia, and dyskinesia. As a measure of manual dexterity, we used the coin rotation (CR) task, requiring patients to rotate a coin between their thumb, index, and middle finger. Maximal grip strength was measured with the GF task. Correlation analyses revealed that both CR and GF performances were associated with different motor abnormalities, most strongly with NSS (CR: tau = -0.263, p < 0.001; GF: tau = -0.208, p < 0.001). Hierarchical regression showed that NSS predicted performance on the CR and GF task better compared to PS, parkinsonism, and catatonia alone (CR: ∆R2 = 0.09, F = 22.26, p < 0.001; GF: ∆R2 = 0.02, F = 6.61, p < 0.001). When looking within the NSS domains, CR performance was predicted better by motor coordination and sequencing of motor acts, whereas GF was predicted better by sensory integration. Motor control processes are influenced by different motor abnormalities, especially NSS. Our results suggest that distinct aspects of NSS affect fine motor movements and GF. This knowledge is important for designing specific novel interventions aimed at improving specific motor control processes.
