  Uncertainty is widely acknowledged as an engaging gameplay element but rarely
used in exergames. In this research, we explore the role of uncertainty in
exergames and introduce three uncertain elements (false-attacks, misses, and
critical hits) to an exergame. We conducted a study under two conditions
(uncertain and certain), with two display types (virtual reality and large
display) and across young and middle-aged adults to measure their effect on
game performance, experience, and exertion. Results show that (1) our designed
uncertain elements are instrumental in increasing exertion levels; (2) when
playing a motion-based first-person perspective exergame, virtual reality can
improve performance, while maintaining the same motion sickness level as a
large display; and (3) exergames for middle-aged adults should be designed with
age-related declines in mind, similar to designing for elderly adults. We also
framed two design guidelines for exergames that have similar features to the
game used in this research.
