Passive leg cycling increases activity of the cardiorespiratory system in people with tetraplegia

Individuals with cervical spinal cord injury (SCI) are at an increased risk for cardiovascular disease. Exercise is well-established for preventing cardiovascular disease; however, there are limited straightforward and safe exercise approaches for increasing the activity of the cardiorespiratory system after cervical SCI. The objective of this study was to investigate the cardiorespiratory response to passive leg cycling in people with cervical SCI. Beat-by-beat blood pressure, heart rate, and cerebral blood flow were measured before and throughout 10 minutes of cycling in 11 people with SCI. Femoral artery flow-mediated dilation was also assessed before and immediately after passive cycling. Safety was monitored throughout all study visits. Passive cycling elevated systolic blood pressure (5 +/- 2 mm Hg), mean arterial pressure (5 +/- 3 mm Hg), stroke volume (2.4 +/- 0.8 mL), heart rate (2 +/- 1 beats/min) and cardiac output (0.3 +/- 0.07 L/min; all p < 0.05). Minute ventilation (0.67 +/- 0.23 L/min), tidal volume (70 +/- 30 mL) and endtidal PO2 (2.6 +/- 1.23 mm Hg) also increased (all p < 0.05). Endothelial function was improved immediately after exercise (1.62 +/- 0.13%, p < 0.01). Passive cycling resulted in an incidence of autonomic dysreflexia. Therefore, passive leg cycling increased the activity of the cardiorespiratory system and improved endothelial function, indicating it may be a beneficial exercise intervention for the cardiovascular and respiratory systems in people with cervical SCI. Novelty: Passive leg cycling increases the activity of the cardiorespiratory system and improves markers of cardiovascular health in cervical SCI. Passive leg cycling exercise is an effective, low-cost, practical, alternative exercise modality for people with cervical SCI.