This systematic review is performed to determine the effects of chemodenervation (Motor Branch Block (MBB) or Neuro Muscular Block(NMB)) of the Rectus femoris muscle on stiff knee gait. Studies selected from 4 electronic data bases included adults suffering from a central neurological disorder with range of knee motion during gait as outcome. Secondary outcomes were walking speed and energy cost. Data from stroke patients were pooled where possible. Peak knee flexion during swing improved in all 8 included studies. Data pooling of stroke patients showed a significant improvement of 7,40 (P=0,002) in the NMB studies and 11,30 (P=0,0009) in the MBB studies. Pooling of walking speed showed no significant difference. A decrease in net energy cost varying from 0.5-0.9 J. kg-1.m-1 (9-15 %) was noted. The only moderate increase in knee flexion does not affect walking speed. The improvement in energy cost might result from decreased knee extensor moment and/or decreased (energy-inefficient) compensations.