Passive exercise therapy for spinal cord injury

Spinal cord injury (SCI) is a devastating condition with loss of multiple functions depending on the level of injury and degree of damage to the spinal cord. SCI results in hyper-reflexia, which is a component of spasticity. Currently, the mechanisms behind hyper-reflexia and spasticity are unknown.; The H-reflex is a compound electromyographic (EMG) response elicited by the synaptic activation of motoneurons by muscle afferents following stimulation of muscle nerves. Many authors have reported the use of frequency-dependent depression of the H-reflex to be valuable for assessing hyper-reflexia.; First, the time course of the reflex changes was observed after complete SCI in the rat. The results of these experiments suggest that hyper-reflexia in the complete transection animal model begins between 7-14 days. Increases in the amplitude of the H-reflex with increased stimulation frequency occurred from 14-30 days compared to intact animals. Additional changes between animals tested at 30 days post transection and animals tested at 90 days post injury were not observed, suggesting that H-reflex had stabilized by 30 days. Secondly, additional studies determined the minimum duration of exercise required to show normalization of the H-reflex. It had been previously shown that passive exercise using motorized bicycle exercise therapy (MBET) for 90 days could be used to normalize H-reflex changes observed after injury. This experiment demonstrated that MBET initiated acutely could normalize reflexes in as few as 30 days of training consisting of one hour per day five days per week. The last experiment compared H-reflex low frequency-dependent depression in animals that had exercise initiated acutely to those whose exercise began after hyper-reflexia had been established. Previous studies had determined the effects of passive exercise if initiated in the acute phase, but the effects of exercise initiated in the chronic state after injury were unknown. Our results suggest that hyper-reflexia can be alleviated if MBET is begun during the chronic phase, but the duration of exercise needed in order to reduce hyper-reflexia is longer.; These studies provide convincing evidence for the potential therapeutic use of MBET as a palliative strategy for SCI.