Influence of Caffeine on HRV and Exercise Performance in Spinal Cord Injury

The aim is to investigate the influence of caffeine on heart rate variability and on performance in a 3 min exercise test in different population groups (able-bodied, paraplegic and tetraplegic subjects). In general, the investigators are interested in the differences between the heart rate variability before and after caffeine supplementation and if the subjects exercise performance is enhanced using this type of supplementation. Another objective is to see whether there are differences between able-bodied and disabled subjects. Tetraplegic subjects showed in some previous studies no Low-Frequency-component (LF) for heart rate variability and no increase in catecholamines after the ingestion of caffeine. Therefore the investigators think, that tetraplegic subjects won't show any ergogenic effect in exercise performance after the intake of caffeine. On the other hand, paraplegic subjects should show similar differences of heart rate variability after the ingestion of caffeine as able-bodied subjects. Paraplegic subjects should benefit from caffeine supplementation in an increase in exercise performance.