On the authors knowledge this is the first study aiming to develop a clinical assessment tool of functional mobility of people with PD during multitasking by means of VR. Thus, in order to verify the VFMT clinical potential, its sensitivity was tested by the performance´s comparison between groups, its feasibility by the correlation between well-established tests, its reproducibility by the intra-rater correlation and the usability by the subjects’ perception of the virtual environment.
The results showed significant differences between groups performances not only in the cognitive and motor clinical tests but also in VFMT tests, except on the TMT-B and CT. Furthermore, the performances in the VFMT tasks presented strong correlations with TMT-A and TMT-B, evaluation of performance in the VFMT tasks presented an excellent reproducibility intra-rater for the CT and VFMT had acceptable usability between the people with PD.
The VFMT was sensitive to differentiate the groups during the motor task but, different than expected, the same did not occur for CT. During the ST, the participant was guided by the therapist to ensure that just the motor task was performed. On the other hand, the CT is a motor-cognitive task in which many cognitive domains are required simultaneously with the motor task. Thus, we believe that the CT must have been difficult even for individuals without disease matched by age to the people with PD, since healthy old adults also present decline in automaticity of movements  which could impairs the execution of simultaneous tasks. In a pilot study (on going publication), our group compared young people and people with PD performances, on the VFMT. Young people did not find difficulties in performing the CT. However, more studies are needed to elucidate this question.
Furthermore, similarly to the CT, the TMT part B was not sensitive to differentiate the groups. Coincidently, in both TMT-B and CT tests, attention and EF are simultaneous with the motor task. Thus, both tests are concurrent high complexity tasks. This supports prior research that suggests higher complexity in concurrent tasks results in a more negative influence of dual tasks for young adults, elderly and people with PD [21, 22, 23].
Furthermore, according to Callegari-Jacques classification , in the PG there were strong correlations between the CT and the TMT part A and B. This result was already expected, once both parts of the TMT are predictive of impaired mobility in elderly people [24, 25]. Even though similar results were not found for people with PD, a reduction on gait speed during DT was observed in people with PD and matched controls [26, 27].
On the other hand, the VFMT seems to be as suitable as TUG test for assessing functional mobility, because moderate correlations were found between TUG and TUG-cog and ST and CT, respectively, in PD group. However, even though both tests evaluate functional mobility, they diverge from each other as they require different motor aspects. The TUG test requires movements as sitting to stand and turning, while the VFMT presents trunk lateral flexion. Furthermore, the TUG-cog allows just one cognitive task associated to the motor task, while on the CT, more cognitive tasks are required.
Strong and moderate intra-rater reliability and reproducibility was found for the CT and ST, respectively. We believe that as ST is a less complex task and as participants received simultaneous instructions, they probably presented a learning effect which is an issue usually found in this type of repeated measures . On the other hand, the CT presented an excellent reliability.
The virtual environment of the VFMT was classified as from acceptable to excellent usability  by the people with PD, reaching a mean score of 77.4. The SUS questionnaire was applied at the end of the first meeting. According to the users, the VFMT is a tool that, besides the benefits presented by a VR environment, it is easy-to-use, motivating and ecological.