  Combining interconnected wearables provides fascinating opportunities like
augmenting exergaming with virtual coaches, feedback on the execution of sports
activities, or how to improve on them. Breathing rhythm is a particularly
interesting physiological dimension since it is easy and unobtrusive to measure
and gained data provide valuable insights regarding the correct execution of
movements, especially when analyzed together with additional movement data in
real-time. In this work, we focus on indoor rowing since it is a popular sport
that's often done alone without extensive instructions. We compare a visual
breathing indication with haptic guidance in order for athletes to maintain a
correct, efficient, and healthy breathing-movement-synchronicity (BMS) while
working out. Also, user experience and acceptance of the different modalities
were measured. The results show a positive and statistically significant impact
of purely verbal instructions and purely tactile feedback on BMS and no
significant impact of visual feedback. Interestingly, the subjective ratings
indicate a strong preference for the visual modality and even an aversion for
the haptic feedback, although objectively the performance benefited most from
using the latter.
