Facilitation of leg muscle activity by active arm movements during locomotor tasks could be beneficial during gait rehabilitation after spinal cord injury. The present study explored the effects of arm movements on leg muscle activity during sub-maximal recumbent stepping. Healthy subjects exercised on a recumbent stepping machine both with and without arm movements. Activity of five leg muscles was recorded and compared for stepping with and without arm movements. To determine which arm movements are optimal for leg muscle facilitation, subjects were instructed to step with 1) mechanically coupled vs. decoupled arm and leg movements, 2) synchronous (SYNC) vs. asynchronous (ASYNC) arm movements and 3) at 50 vs. 70 revolutions per minute (RPM). Leg muscle activity was increased by active arm movements in all muscles, except the vastus lateralis (VL) muscle. Activity of other extensors (soleus (SO), medial gastrocnemius (MG) and biceps femoris (BF)) was primarily increased during the extension phase whereas activity of flexors (tibialis anterior (TA)) was also increased during the flexion phase. Facilitation was more or less consistent for both frequencies and for SYNC and ASYNC movements. For coupled arm movements facilitation tended to be diminished or absent. The observed facilitation in the present study is probably of neuromuscular rather than of biomechanical origin, since the arms are probably hardly involved in postural control or weight-bearing during recumbent stepping. Further studies in patients should explore the possibility to integrate neuromuscular facilitation in rehabilitation programs.