Effects of crank length on the cardiovascular response in a rat model of motorized cycling

Longitudinal pre-clinical study.

To determine the impact of crank length and cadence on pedal reaction forces and cardiovascular responses in a preclinical model of high thoracic severe spinal cord injury.

The Kentucky Spinal Cord Injury Research Center at the University of Louisville, Louisville, KY USA.

Five female Sprague-Dawley rats received T2 severe contusion SCIs and served as their own controls. To better understand the biomechanical and cardiovascular responses to cycling, we utilized a commercially available motorized rat cycle with custom cranks and pedals to collect pedal reaction forces using two different crank lengths and at a range of cycling cadences. Simultaneously, heart rate (HR) and blood pressure (BP) were collected via an indwelling telemeter. Collected data were analyzed pre-, during, and post-cycling, weekly up to six weeks post-injury.

The longer crank length increased forces and spasticity, although differences were more pronounced during extension that involved lengthening of the flexor muscles. HR and systolic/diastolic pressures were elevated during cycling and changed in parallel with force events, although few differences were observed between standard and short crank length cycling.

These results suggest that MC may constitute a mild exercise strategy post-SCI; clinical translation may be dependent on the ability of the subject-specific cycling parameters to generate reflex-induced eccentric muscle contractions during cycling, emphasizing the importance of crank length (leg range-of-motion) and cycling cadence on the value of motorized cycling after severe SCI.