Task-specificity vs. ceiling effect: Step-training in shallow water after spinal cord injury

Abstract

While activity-based rehabilitation is one of the most promising therapeutic approaches for spinal cord injury, the necessary components for optimal locomotor retraining have not yet been determined. Currently, a number of different activity-based approaches are being investigated including body weight-supported treadmill training (with and without manual assistance), robotically-assisted treadmill training, bicycling and swimming, among others. We recently showed, in the adult rat, that intensive rehabilitation based on swimming brought about significant improvements in hindlimb performance during swimming but did not alter the normal course of recovery of over-ground walking . However, swimming lacks the phasic limb-loading and plantar cutaneous feedback thought to be important for weight-supported step training. So, we are investigating an innovative approach based on walking in shallow water where buoyancy provides some body weight support and balance while still allowing for limb-loading and appropriate cutaneous afferent feedback during retraining. Thus, the aim of this study is to determine if spinal cord injured animals show improved overground locomotion following intensive body-weight supported locomotor training in shallow water. The results show that training in shallow water successfully improved stepping in shallow water, but was not able to bring about significant improvements in overground locomotion despite the fact that the shallow water provides sufficient body weight support to allow acutely injured rats to generate frequent plantar stepping. These observations support previous suggestions that incompletely injured animals retrain themselves while moving about in their cages and that daily training regimes are not able to improve upon this already substantial functional improvement due to a ceiling effect, rather than task-specificity, per se. These results also support the concept that moderately-severe thoracic contusion injuries decrease the capacity for body weight support, but do not decrease the capacity for pattern generation. In contrast, animals with severe contusion injuries could not support their body weight nor could they generate a locomotor pattern when provided with body weight support via buoyancy.

Stretching adversely modulates locomotor capacity following spinal cord injury via activation of nociceptive afferents.

“…Unlike human SCI subjects, animals with only 5-10% spared white matter achieve significant locomotor recovery [188]. One of the biggest differences between human subjects and rats with SCIs is the state of mobility after the traumatic event.…”

“…In addition, hindlimb kinematics and gait were assessed using digital video (sagittal and ventral views) acquired while the animals stepped in 2" (5 cm) of water sufficient to supply approximately 60% body weight support, as described previously [188]. We used a 3-segment, 2-angle model of the hindlimbs for kinematic analysis with Columbiaville, MI) and custom designed Excel macros [185,186].…”

Effects of telemetry EMG implants on hindlimb locomotor recovery in thoracic spinal contused rats.

“…These assessments are used to measure range of motion in hindlimbs using peak/trough/excursion (PTE) of two angles based on points placed on the hip, ankle, and toe (HAT) and the iliac crest, hip, and ankle (IHA) (Kuerzi et al, 2010;Caudle et al, 2011). Forelimb-hindlimb coordination was measured using plantar stepping index (PSI) and regularity index (RI), as described in the aforementioned studies.…”

“…Overground kinematics were analyzed for range of motion and limb movement/positions according to our standard protocol (Kuerzi et al, 2010;Caudle et al, 2011). Statistics.…”

“…As assessed by the BBB Open Field Locomotor Scale, a measure of hindlimb function during overground stepping (BBB; Basso et al, 1996), rats from injured (untrained) control groups achieved scores of 13-15 or 10-12 for moderate or moderately-severe injuries, respectively, and neither swim training nor shallow-water training improved BBB scores (Kuerzi et al, 2010;Magnuson et al, 2009;Smith et al, 2006). We first attempted to address the effects of in-cage retraining using a hindlimb immobilization model.…”