## Abstract
The rich stimuli environment, with the continuous audio-visual feedback, that virtual reality training can provide enhances the learning process of new exercise strategies and it has been extensively used for improving balance and gait in older adults [26; 27; 28]. However, these new technological devices, wearable electronics, immersive virtual environments and virtual-reality-based games, although very promising and user friendly, have not been thoroughly investigated for the side effects that may be caused, such as dizziness and eye fatigue [29]. In addition, the long-term effects are not very well known yet and, further still, they are not very easily accessible for group-based rehabilitation which always provides a more socializing aspect in rehabilitation. On the other hand, the OEP has the advantages of multi-sensory stimuli and its group-based method of delivery expands the social participation of older adults and enable them to obtain good compliance and satisfaction [14; 30]. The OEP places great emphasis on verbal guidance and the demonstration of the exercise, so that the participant realizes and performs the exercise correctly. Therefore, it is possible that the benefits of the OEP can be attributed to additional elements such as the correct perception of the posture, the correct execution of the exercise through verbal guidance (command, sequence), and the understanding of the usefulness of the exercise, not just the execution of the exercise itself. Indeed, the importance of feedback during skill acquisition, the type of feedback and the frequency with which this is provided has been extensively discussed in the literature [31; 32]. However, the efficacy of the time that this feedback and guidance is given is still unclear and the effectiveness of the OEP exercise guidance regarding delivery time on balance, gait, and cognition has never been explored. It is believed that the feedback given during the performance of a task is important for facilitating performance because it guides the learner to the correct movement pattern; however, it is assumed to have negative effects in learning, because the participant becomes dependent on the feedback and neglects the processing of intrinsic feedback [23]. On the other hand, if a participant is asked to reproduce a task by first receiving a demonstration of it and instructions for it, without any other feedback during the performance of the task, this may better promote the skill acquisition and motivation of the participant [33]. The visual demonstration of motion engages the active learning process, because the learner should recognize the movement pattern, replicate the pattern from what the movement is perceived (recognized) to be, and have some control and decision-making during the reproduction of the movement [33]. This active participation may be more efficient for skill acquisition than a passive process which is produced by just providing concurrent feedback for movement correction during the task [34]. The purpose, therefore, of this study is to examine whether visual demonstration and verbal guidance and correction of exercises, before the exercise program conduction vs. during the exercise program conduction alone, is more effective in improving balance, gait, cognitive function, and fear of falling in the older adults. Thus, this research aims to answer the question of: when is exercise guidance more beneficial for the physical and cognitive function of older adults, when it is given before or during the exercise performance? We hypothesize that guidance given before the exercise is more mentally demanding for the participants and, thus, engages more physiological processes of active learning which may be more efficient for improving physical and mental health and for maintaining motivation and adherence to the exercise.