Insufficiency of trunk extension and impaired control of muscle force in Parkinson’s disease with camptocormia

Abstract Objective To examine the aetiology of parkinsonian camptocormia, a non-fixed pathological forward bending of the trunk, by measuring trunk muscle activation and force regulation in Parkinson patients with (PD+CC) and without (PD) camptocormia matched for disease severity, and in age- and sex-matched healthy controls (HC). Methods The isometric forces of trunk extension and flexion were measured in PD+CC, PD and HC. Neuromuscular efficiency (increase of extension force per increase of paravertebral muscle surface electromyography signal) and the ability to maintain a constant submaximal trunk extension force were examined. Results Peak trunk extension force was significantly lower in PD+CC and PD than in HC, with PD+CC non-significantly weaker than PD. Compared with HC and with PD, the neuromuscular efficiency of trunk extension was significantly reduced in PD+CC. The variability of the force output (coefficient of variation) was significantly larger for PD+CC than for HC or PD. Conclusion The reduced neuromuscular efficiency of trunk extension separates PD+CC from PD. Moreover, control of the trunk extensor force is impaired in PD+CC. Significance There is weakness and a force control deficit in parkinsonian camptocormia suggesting a disturbed sensory-motor integration, which may contribute to myopathic changes in the trunk extensor muscles.