Effects of Different Exercise Doses Through an Augmented Reality Exergame in Older Adults: A Pilot Randomized Controlled Trial  
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1 Toledo Physiotherapy Research Group (GIFTO), Faculty of Physical Therapy and Nursing, Universidad de Castilla-La Mancha, 45071 Toledo, Spain; [EMAIL_ADDRESS] (J.B.-A.); [EMAIL_ADDRESS] (D.M.-C.A.)  
2 Toledo Physiotherapy Research Group (GIFTO), Instituto de Investigacion Sanitaria de Castilla-La Mancha (DISCAM), 45071 Castilla-La Mancha, Spain 2  
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[PERSON]  
1 Toledo Physiotherapy Research Group (GIFTO), Faculty of Physical Therapy and Nursing, Universidad de Castilla-La Mancha, 45071 Toledo, Spain; [EMAIL_ADDRESS] (J.B.-A.); [EMAIL_ADDRESS] (D.M.-C.A.)  
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Footnote 1: email: {h.breviv.dapricia.  
Physical activity is defined as any bodily movement produced by skeletal muscles that results in energy expenditure [7]. Exercise, on the other hand, is a subset of physical activity that is planned, structured, and repetitive and is aimed primarily at improving physical fitness [7]. Following the recommendations of the American College of Sports Medicine (ACSM), exercise prescriptions should adhere to the FITT principles: frequency, intensity, type, and time [8]. However, adding a fifth 'F' representing fun has been suggested because of its importance in exercise adherence [9].  
Exercise intensity refers to the rate of energy demand during physical activity [10]. To measure the desired intensity, several tools provided objective data, such as heart rate (HR), and subjective data, such as the Borg Rating of Perceived Exertion (RPE) [10]. Numerous studies have reported a strong correlation between HR and the RPE, validating both measures as indicators of exercise intensity [11]. Nevertheless, this relationship may be altered in the context of exergames, as the introduction of visual and auditory stimuli could lead to a decrease in perceived RPE [12; 13].  
The primary goal of engaging in physical activity or exercise is to achieve the optimal stimulus without compromising the safety of the individual or inducing adverse side effects. Engaging in physical activity is associated with a 19% increase in the risk of non-serious adverse effects, with pain and fatigue being the most common complaints [14]. Understanding how exercise exposure, in terms of intensity and duration, is related to the occurrence of these adverse effects is essential for observing the dose-response relationship and for improving safe and effective exercise recommendations.  
Exercise provides numerous health benefits because of its various modalities [15; 16]. However, the enjoyment and satisfaction derived from the type of exercise used are often overlooked. The literature presents inconsistencies regarding the enjoyment associated with exergames. Some studies suggest that not all individuals find these video games enjoyable, with preferences leaning toward other forms of physical activity [17; 18]. Conversely, other research indicates that exergames can elicit a high level of enjoyment, particularly when played in pairs [17; 18]. These discrepancies may stem from factors such as patient preferences, self-efficacy, or social influences [17]. This aspect is crucial as enjoyment could be a key factor in adherence to treatment, as previously described in older adults, potentially encouraging individuals to exercise more regularly and at higher intensities [18; 19; 20; 21].  
Thus, for these reasons, this study aims to provide evidence on how different exergame doses may influence exercise intensity, perceived exertion, and enjoyment in older adults. Additionally, the study will examine the occurrence of adverse effects, with the goal of optimizing exercise strategies in clinical practice.