[en] The Internet has been expanded worldwide to become the most important mean to spread information in the world (Kocyigit et al., 2019). Searching and finding health information using the Internet has become progressively common while people often use the Internet as a source of health information (Baker et al., 2021; Kocyigit et al., 2019; Sui et al., 2022). According to Amante et al (2015), nearly fifty per cent of adults in the United States (US) get health-related information on the Internet (Amante et al., 2015). As a popular video sharing site, YouTube is extensively used all around the world for users to watch and share videos (Amante et al., 2015; Baran & Yilmaz Baran, 2021; Lewis et al., 2012; Oydanich et al., 2022; Shun Zhang et al., 2020). Due to the free content of its videos and its ease of reach to the population, YouTube can be considered an effective resource for obtaining and disseminating healthrelated information. Consequently, it can also be used as a useful tool for patient education (Chang & Park, 2021; Jessen et al., 2022; Katz & Nandi, 2021; Warren, Wisener, et al., 2021). However, there are doubts about the quality, reliability and content of the videos (Piskin et al., 2021; Shun Zhang et al., 2020). Especially in view of YouTube's philosophy, where anyone can upload videos without prior check or scrutiny, and which could be used for promotional ends, it is necessary to verify the quality, content and accuracy of the information shared in the uploaded videos (McMahon et al., 2022; Yildiz & Toros, 2021). This means that YouTube videos may raise concerns about the risks of providing misleading health-related information in videos available on this platform (Baran & Yilmaz Baran, 2021; Culha et al., 2021; Dubey et al., 2014; Madathil et al., 2015; Patel et al., 2022). A previous systematic review investigating eighteen pieces of research found that YouTube can display misleading and conflicting health-related information, but, on the other hand, it can also share high quality health-related information (Chang & Park, 2021; Oydanich et al., 2022; Yildiz & Toros, 2021). So, digital platforms are a promising way to support physical activity levels and may have provided an alternative for people to maintain their activity while at home (Güloğlu et al., 2022; Kadakia et al., 2022; McDonough et al., 2022; Parker et al., 2021). Therefore, the aim of this study was to assess the quality of YouTube videos, that any internet user could access, regarding to the recommended exercises that are related to topics of major importance for general population. In this regard, exercises related to the most common types of cancer in women and men (breast cancer and prostate cancer, respectively) have been considered, as well as those recommended for periods of confinement due to the global pandemic caused by CoVid-19. Article 1 The prolonged immobilization suggested after breast cancer (BC) surgery causes morbidity. Patients search the Internet, especially social networks, for recommended exercises. The aim of this observational study was to assess the quality of YouTube videos, accessible for any patient, about exercises after BC surgery (Rodriguez-Rodriguez, Blanco-Diaz, Lopez-Diaz, de la Fuente-Costa, Duenas, et al., 2021). Article 2 Prostate cancer (PC) is a major cause of disease and mortality among men. Surgical treatment involving the removal of the prostate may result in temporary or permanent erectile dysfunction (ED) and urinary incontinence (UI), with considerable impact on quality of life. (QoL) Pelvic floor muscle training (PFMT) is one of the recommended techniques for the prevention, treatment, and rehabilitation of postoperative complications. The aim of this observational study was to assess the quality of YouTube videos related to exercises after prostatectomy surgery (Rodriguez-Rodriguez, Blanco-Diaz, Lopez-Diaz, de la Fuente-Costa, Sousa-Fraguas, et al., 2021). Article 3 The world has been experiencing a pandemic caused by COVID-19. Insufficient physical activity can increase the risk of illness. The aim of this study was to evaluate the quality of YouTube videos related to home exercises during lockdown and their adherence to WHO recommendations after replicating a simple search process that could be performed by any individual internet user (Rodriguez-Rodriguez et al., 2022).

[es] Internet ha sufrido una expansión incomparable hasta convertirse en el medio más importante de difusión de información en el mundo (Kocyigit et al., 2019). Buscar información sobre salud en Internet se ha convertido en algo progresivamente común hasta el punto de que los usuarios suelen utilizar Internet como fuente primaria de información sobre temas relacionados con la salud(Baker et al., 2021; Kocyigit et al., 2019; Sui et al., 2022). Según Amante et al. (2015), casi el cincuenta por ciento de los adultos en los Estados Unidos (EE.UU.) obtienen información relacionada con la salud a través de Internet(Amante et al., 2015). Como portal web popular para ver y compartir vídeos, YouTube es utilizada ampliamente a nivel mundial para ver y compartir vídeos (Amante et al., 2015; Baran & Yilmaz Baran, 2021; Lewis et al., 2012; Oydanich et al., 2022; Shun Zhang et al., 2020). Debido al contenido gratuito de sus vídeos y a su facilidad para llegar a la población, YouTube puede considerarse como un recurso eficaz para obtener y difundir información relacionada con la salud y utilizarse como una herramienta útil para la educación de los pacientes (Chang & Park, 2021; Jessen et al., 2022; Katz & Nandi, 2021; Warren, Wisener, et al., 2021). Sin embargo, existen dudas razonables sobre la calidad, la fiabilidad y el contenido de los vídeos (Piskin et al., 2021; Shun Zhang et al., 2020). El sistema de carga de YouTube, permite incluir vídeos sin control ni escrutinio previos. Es por ello necesario verificar la calidad, el contenido y la exactitud de la información compartida (McMahon et al., 2022; Yildiz & Toros, 2021). Los vídeos de YouTube pueden compartir información de alta calidad relacionada con la salud pero también suscitan preocupación por los riesgos de proporcionar información de baja evidencia científica (Baran & Yilmaz Baran, 2021; Chang & Park, 2021; Culha et al., 2021; Dubey et al., 2014; Madathil et al., 2015; Oydanich et al., 2022; Patel et al., 2022; Yildiz & Toros, 2021). Por lo tanto, el objetivo de esta tesis doctoral fue evaluar la calidad de los vídeos de YouTube en cuanto a los ejercicios recomendados que están relacionados con temas de gran importancia para la población general, como son los tipos de cáncer más comunes en las mujeres y en los hombres (cáncer de mama y de próstata, respectivamente), así como los recomendados para los períodos de confinamiento en los domicilios de la población debido a la pandemia mundial causada por el CoVid-19.