To assess the effectiveness of simulated breathing in virtual reality (VR) for manipulating the level of perceived effort of people with long COVID during sessions of physical rehabilitation.

We conducted a within-participants randomized prospective study during a cycling exercise in immersive VR with three counterbalanced conditions of simulated breathing: slower breathing, neutral breathing, and faster breathing compared to theirs. 37 participants with long COVID and deconditioning were included in the study, 36 of which could finish the experiment.

The study did not show any influence of the rate of the simulated breathing on participants' perceived effort, which was the primary judgment criterion. We did not find any effect of simulated breathing rate on perceived fatigue, cybersickness and embodiment (VR metrics), and preference. However, higher actual breathing rates were observed in the condition with faster simulated breathing.

The study did not show the effectiveness of using simulated breathing in VR to manipulate perceived effort during the physical rehabilitation of people with long COVID. Nevertheless, our results suggest that this technique is feasible, as only one participant dropped out due to their symptoms, as most participants had a good appreciation of the system, and reported feeling rather strong embodiment and weak cybersickness.