Exploring methods for targeted activation of the sympathetic nervous system without exercise

When using functional electrical stimulation (FES) for cycling in individuals with spinal cord injury (SCI) during FES-cycling, a rapid onset of muscular fatigue can be observed. Among other reasons, missing neural feedback from the lower extremities might be responsible for a reduced sympathetic response during stimulation. Therefore, this project explores different methods to activate the sympathetic nervous system to increase the heart rate to allow better blood circulation and oxygenation in the working muscles. Six techniques were selected to be tested on 10 healthy participants in the context of pilot measurements. Those were the cold pressor test with both hands, a virtual reality roller-coaster ride, the hot water immersion test with two hands, the Wim Hof breathing method, the Valsalva manoeuvre and the ingestion of Capsaicin through Prik Jinda chilli peppers. The results showed a significant increase in average as well as peak heart rate during all methods performed. From baselines of around 68±1.3 bpm, the strongest increases in both parameters were found for the Valsalva manoeuvre (to 118±20.9 bpm peak, 91±14.2 bpm average), the Wim Hof breathing method (to 112±13.5 bpm peak, 86±11.8 bpm average) and Capsaicin ingestion (to 103±18.9 bpm peak, 80±16.7 bpm average). The methods as they were performed in this project, are not all directly applicable to FES-Cycling but rather serve as exploration how efficiently which stimuli can increase the heart rate. In future research, adaptation or combination of techniques might help to increase performance during FES-Cycling.