Background The application of resistive forces has been used during body weight supported treadmill training (BWSTT) to improve walking function after spinal cord injury (SCI). Whether this form of training actually augments the effects of BWSTT is not yet known. Objective To determine if robotic-applied resistance augments the effects of BWSTT using a controlled experimental design in a rodent model of SCI. Methods Spinally contused rats were treadmill trained using robotic resistance against horizontal (n=9) or vertical movements (n=8) hindlimb movements. Hindlimb stepping was tested before and after 6 weeks of training. Two control groups, one receiving standard training (i.e. without resistance; n=9) and one untrained (n=8), were also tested. At the terminal experiment, the spinal cords were prepared for immunohistochemical analysis of synaptophysin. Results Six weeks of training with horizontal resistance increased step length while training with vertical resistance enhanced step height and movement velocity. None of these changes occurred in the group that received standard (i.e. no resistance) training or in the untrained group. Only standard training increased the number of step cycles and shortened cycle period toward normal values. Synaptophysin expression in the ventral horn was highest in rats trained with horizontal resistance and in untrained rats and was positively correlated with step length. Conclusions Adding robotic-applied resistance to BWSTT produced gains in locomotor function over BWSTT alone. The impact of resistive forces on spinal connections may depend on the nature of the resistive forces and the synaptic milieu that is present after SCI.

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