Recruitment modulation of force fields organized in the frog´s spinal cord

Convergent force fields organized in the frog´s spinal cord could be used as a new functional neuromuscular stimulation (FNS) technique to restore motor function using electrical stimulation of the spinal interneurons. We studied the recruitment modulation of these force fields to four parameters of the electrical microstimulation stimulus train. The parameters modulated were the stimulation frequency, the pulse duration, the pulse amplitude, and the train duration. We found that all four parameters can be used to modulate the force level, and that all the parameters but train duration also affect the force rate of rise. Furthermore, we found that the vectorial structure of the fields was not affected by the force modulation, as the normalized fields were nearly identical. These early results demonstrate the possibility of modulating the action of the fields while retaining their useful convergent property