## Materials and Methods  
### Description and Benefits of the HybridPLAY Technology  
HybridPLAY is a concept that combines traditional game and digital video games, creating a new kind of game especially designed to be used in urban spaces and mainly made up of physical activity and social interaction. The main element of HybridPLAY is a sensor (see Figure 1) that consists of an electronic circuit and a plastic casing that is connected by means of a clamp mechanism to the equipment of public playgrounds, such as seesaws, swings, slides, etc., and it turns them into physical interfaces to control video games in our mobile phones. This sensor captures the data (acceleration, speed, inclination, etc.) of the movements on these elements and it sends the data to the mobile phone where they are analyzed and transformed into actions that control the various video games: Jump, run, turn, hit, etc. The main components of the HybridPLAY sensor are: An ATmega32U4-AU processor (compatible with Arduino), a micro-USB connector, a three-axis accelerometer and gyroscope, an infrared proximity sensor, a LED button and a sound component. The mini-games were developed for both smartphone and tablet devices, and for both Android and iOS platforms. We initially used the game engines Cocos2-dx and Unity. Therefore, any mobile device with iOS 7.0 or higher or with Android 5.0 or higher--which means almost all of current mobile devices--is enough to run the mini-games. The connectivity of the sensor with the mobile phone is achieved with Bluetooth LE. The batteries of the sensor can last up to 20 h, while the duration of the batteries of the mobile phone depends on the one used. No cloud services are need, since HybridPLAY involves just the sensor and a mobile device connected to it, with a software application running on this latter device. More details on the technological aspect of HybridPLAY can be found in Reference [9] (refer to version 3 of the sensor). HybridPLAY combines digital and physical interaction to create experiences of outdoor game where the dynamics of digital video games are combined with game strategies in the street, verbal and body communication and group play (Figure 2). The system has been tested and evaluated in different game situations, offering very satisfactory results, due to its mechanical versatility, as it adapts to a wide range of surfaces and materials, facilitating its use in equipment with a tubular structure and/or made of wood. It also provides different levels of complexity through the combination of a digital and a physical experience. The system combines the dynamics of video games with those of motor play, understood as motion systems that involve the combination of intention, decision and adjustment of the motor functions to the different logical contexts and situations [14]. HybridPLAY falls within the category of the so-called active video games, but it has differentiating features that extend the possibilities of interaction of these games and their mechanics, both in the strictly physical and symbolic aspect. These differences refer to:  
* Outdoor play. The system is designed to be played in outdoor playgrounds so that it implies a number of benefits related to the use of these places, such as socialization, the benefits of outdoor  
Figure 1: Descriptive image of the HybridPLAY system. Figure 2: Parents and children playing with HybridPLAY, for the original version of the system [9]. activities and being in touch with nature, etc. Whereas active video games are also tools for group participation and they facilitate physical exercise, their implementation in indoor spaces of the domestic sphere limits interaction and prevents spontaneous interaction with other people. * Mobility. The system, unlike most common active video games, is designed to be easily carried and played in different places, given its small size and its energy autonomy. It is also combined with the personal mobile phone of players, something that allows taking the gaming experience to different places easily.