## 5 Virtual Reality (VR) and Augmented Reality (AR) in Sports Performance Analysis  
### Definition and History  
VR is a technology that immerses users in computer-generated environments, transcending the boundaries of physical reality and enhancing users' experiences and engagement, including visual, auditory, and tactile cues [28; 110]. It encompasses various system categories, including Non-Immersive, Semi-Immersive Projection, and Fully Immersive systems [110]. On the other hand, AR can be defined as a dynamic fusion of the virtual and real, seamlessly integrating virtual entities within real-world environments in real time, enabling users to interact with both domains [29; 111; 112]. The concept of VR has its origins dating back to the 1960s when Morton Heilig, an American cinematographer, created the Sensorama--a mechanical device aimed at providing a multisensory experience through stereoscopic 3D images, sounds, smells, and even vibrations [113]. In the late 1960s and early 1970s, Ivan Sutherland developed what is often considered the first true head-mounted display (HMD) system, called the \"Sword of Damocles\" [114]. However, it was not until the 1980s and 1990s that VR technology began to take a more concrete shape with advancements in computer graphics, display technology, and interaction devices. In fact, the term \"virtual reality\" was only coined in the 1990s by Jaron Lanier [115]. Also, in the 1990s, the Computer Automatic Virtual Environment (CAVE) systems were introduced, offering a fully immersive environment [116]. This technology enables users to fully experience and interact with 3D computer-generated environments within a spacious cube formed by multiple display screens. As users physically enter this projection cube, they become fully enveloped by the virtual environment and a more natural and realistic sense of being [34]. Similarly, the AR concept dates back to the 1950s, with the term being coined by Tim Caudell and David Mizell in 1990 [110, 117]. AR systems can be head-mounted see-through and monitor-based video systems [110, 111]. While there are some conceptual differences between VR and AR, both technologies share a common goal: enhancing user experiences by extending possibilities beyond the physical world through seamless and harmonious interactions [29, 110]. In fact, some argue that both should be enclosed by the same comprehensive framework under the term 'XR', where X works as a placeholder for any reality [33, 110]. It is evident that the development of both VR and AR relies on an inherent relationship with emerging technologies. As a result, the extensive utilization of these technologies hinges on the commercial availability of the associated devices. In recent decades, significant progress has been made in the VR and AR landscape, leading to the creation of a variety of devices catering to different levels of immersion and functionality (Table 2). From the pioneering attempts of SEGA VR and Google Glass, to the more recent Microsoft HoloLens and Meta Quest 2 & 3, and the recently introduced Apple Vision Pro, these devices have the power to transform how we perceive and interact with both the virtual and real worlds, paving the way for innovative applications in fields such as medicine and physiotherapy [118, 119, 120, 121, 122], manufacturing [31, 123], entertainment [31, 124], exercise [125, 126], and education [124, 127, 128, 129]. It is evident that sports performance analysis also benefited from the development and convergence of VR and AR, opening a new realm of possibilities to enhance training, skill development, and overall athletic performance [30, 32, 33, 34].