FULL WEIGHT-BEARING HINDLIMB STANDING FOLLOWING STAND TRAINING IN THEADULT SPINAL CAT

Behavioral and physiological characteristics of standing were studied in nontrained spinal cats and in spinal cats that received daily stand training of the hindlimbs for 12 wk. Training consisted of assisting the cats to stand with full weight support either on both hindlimbs or on one hindlimb (30 min/day, 5 days/wk). Extensor muscle electromyogr aphic (EMG) amplitude and extension at the knee and ankle joints durin g full weight bearing recovered to prespinal levels in both stand-trai ned and nontrained spinal cats. However, full weight bearing of the hi ndquarters was sustained for up to similar to 20 min in the spinal cat s that received bilateral stand training compared with similar to 4 mi n in cats that were not trained to stand. Unilateral stand training se lectively improved weight bearing on the trained limb based on ground reaction forces and extensor muscle EMG activity levels measured durin g bilateral standing. These results suggest that the capacity of the a dult lumbar spinal cord to generate full weight-bearing standing can b e improved by as much as fivefold by the repetitive activation of sele cted neural pathways in the spinal cord after supraspinal connectivity has been eliminated. Given that stepping is improved in response to s tep training, it appears that the recovery of standing provides anothe r example of training-specific motor learning in the spinal cord, i.e. , the spinal cord learns to perform hindlimb standing by practicing th at specific task.