Corticospinal and spinal excitability to the biceps and triceps brachii is modulated differently between forward and backward arm cycling

Abstract

Research on humans and non-human animals has provided indirect evidence that suggests that the fundamental rhythmic motor pattern required for locomotor outputs is partially controlled by neural circuits in the spinal cord, referred to as the central pattern generator (CPG). Specifically, research has shown that the same neural networks operate to control both forward (FWD) and backward (BWD) locomotor outputs. Up until this point researchers have focused on examining reflex modulation patterns during FWD and BWD locomotor outputs to infer activity of the CPG. However, these studies do not provide any insight into how the brain and spinal cord are contributing to the generation of FWD and BWD rhythmic movement. To date, no study has directly compared corticospinal and spinal excitability between FWD and BWD locomotor outputs. Thus, the purpose of this study was to use transcranial magnetic stimulation (TMS) in combination with transmastoid electrical stimulation (TMES) to compare corticospinal and spinal excitability projecting to the biceps and triceps brachii between FWD and BWD arm cycling.