Abstract
This experiment examines the proposition that sinus arrhythmia is a measure of mental load. The experiment involved a subtraction task in which the physical and mental loads could be varied independently. The results indicate that sinus arrhythmia does decrease with on increase in mental load. However, heart rate can also be used to differentiate between the mental loads. In addition it was found that both heart rate and sinus arrhythmia increased for an increase in physical load. This increase in sinus arrhythmia can be explained by the static work component of the physical load and the scoring system used. It is concluded that changes in heart rate and sinus arrhythmia are best regarded as generalised responses to the imposition of a load.