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

Abstract

STUDY DESIGN: Longitudinal pre-clinical study. OBJECTIVES: 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. SETTING: The Kentucky Spinal Cord Injury Research Center at the University of Louisville, Louisville, KY USA. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.