Effects of Incomplete Spinal Cord Injury on Ventilatory Response to Exercise Following Overground Locomotor Training

Abstract

Individuals with Spinal Cord Injuries (SCI) experience decreased lung volumes, ambiguous minute ventilation (VE), increased fatigability, and decreased performance. Previous research has shown improved VO2 kinetics, walking performance, decreased VO2, and reduced VE variability without a change in VE following overground locomotor training (OLT). However, it is unclear if this reduction in VE variability influenced walking performance. Purpose: This study aimed to characterize the VE and tidal volume (VT) response, it’s variability, and if it affected performance before and after OLT. Participants: 8 motor incomplete cervical SCI (age 37.9±18.2 yrs; BMI 25.1±4.6 kg·m2). 7 individuals between C2-C6 and 1 individual sustained a T7 lesion; all capable of step initiation and independent standing. Methods: OLT consisted of part to whole practice guided by the following principles: practice variability, progressive overload, and task-specificity. Individual training sessions included 5 segments: ground preparation, standing preparation, task-isolation, task-integration and activity rehearsal. Training occurred 2x/week for 90 minutes with program duration of 12 weeks. Two protocols were used in this study. Both protocols started with 3 minutes of standing rest followed by 6 minutes of walking at preferred walking speed. Following this bout, individuals were seated for 4 minutes before returning to a 2-minute standing baseline. At the end of this 6-minute rest bout, two different exercise bouts were used. Protocol 1: 6 minutes at above preferred walking speed (self-selected). Protocol 2: walking at preferred walking speed until volition fatigue or 30 minutes. Results: Protocol 1: VE and VT variability were reduced by 19.4 and 26.9%, respectively. The reduction in variability as associated with a reduction in RPE at each 2 minute time point by 7.6, 39.3 and 17.6% after OLT. Protocol 2: VE and VT variability were reduced by 18.99 and 6.8%, respectively. Additionally, after OLT, all individuals were able to maintain steady-state VE prior to volitionally ending the test. Two individuals were able to successfully finish the 30-minute bout. Conclusion: It appears individuals with a motor incomplete SCI are capable of a hyperpneic response to exercise following a previous bout of exercise. Furthermore, the variability in the ventilatory response is reduced after training and may be implicated in volitional treadmill walking performance in these individuals.