Is the Heart Period Variability-based usability measurement of mental effort robust enough against arm movements?

The mid-frequency (MF) component of the heart rate variability is an often used method of measuring changes in the level of mental effort during human-computer interaction. However, sometimes the exact cause of a change is not self explanatory. There are certain factors, aside from mental effort, that can influence the power level of the MF band: limb movement is one such factor. In this preliminary study, we examined the impact of relatively big arm movements on the power of the MF band. Participants played a game where they had to solve simple equations under a time pressure. In one of the conditions, they also had to raise their non-dominant hand every time they entered an answer. The analysis of our data seems to suggest that the kind of arm movements, used in the experiment, had no significant effect on the MF power. However, further exploration is required to identify what kinds of movements are capable of influencing this particular power band.