Primary objective: The aim of the present study was to evaluate the association of contractures with an increase or reduction of non-spastic muscle overactivity due to severe cerebral damage. Methods and procedures: Forty-five patients with tetraparesis after severe cerebral damage were investigated. Three groups were defined based on the presence of spasticity (revealed as resistance to passive stretch (= hypertonia)), and the presence of contracture of the relevant knee joint: Group_s (17 patients with hypertonia without contracture), Group_s+c (20 patients with hypertonia and contracture), and Group_c (eight patients without hypertonia and with contracture). In all groups spontaneous involuntary muscle activity was assessed continuously over a 12-hour period through isometric measurement of knee joint flexion torque. A mathematical algorithm differentiated an hourly muscle activity spectrum (PI_h). The frequency of peaks (peaksh) from the activity spectrum was determined. Main outcomes and results: We revealed that Groups had higher PI_h and more frequent peaksh compared with Group_s+c and Groupc (p ≤ 0.05). Groupc had comparable PI_h and peaks_h compared with Group_s+c (p ≥ 0.05). Conclusion: The presence of contractures was associated with lower involuntary muscle overactivity in terms of lower PI_h and less frequent peaks_h, indicating that contractures may be associated with reduced non-spastic positive features of the upper motor neurone syndrome in patients with severe brain damage.