The use of a robotic body weight support mechanism to improve outcome assessment in the spinal cord injured rodent

This paper describes the use of a robotic device to assess rodent locomotor ability following spinal cord injury by quantifying the amount of external body weight support required by the animal to step on a treadmill. Precisely controlled, upward forces were delivered to the rat torso through the use of a specially designed counterbalance system. The system utilized an electric motor to alter spring tension in a specific kinematic configuration, which enabled support to be changed rapidly (within a step) in order to adapt to the animal´s specific needs, or to challenge the animal´s capability. Spinal cord transected rats were trained to step while the amount of external body weight support was progressively decreased during several minutes of locomotion on a treadmill, i.e. the rats increasingly supported more of their own body weight. Each animal failed to step at a consistent amount of weight assistance (test-retest reliability=0.92). During three months of daily training, the rats demonstrated an improvement in their ability to support body weight (p=0.04). The system´s unique ability to precisely quantify body weight support allows for a continuous measurement of what was previously a binary assessment, i.e. the animal can support body weight or it cannot, and augments the information derived from current outcome measurement techniques.