## 3 Wireless Sensor Networks (Internet of Things--IoT)
### Sensor Networks: Wireless Transmission Systems  
The technological advances in miniaturized low-power sensors described in the previous section allowed the implementation of WBAN, or a simple body area network, suitable for applications in both medical and non-medical fields. These networks consist of sensors (whose number and nature continuously increase), embedded processors, and transceivers. In addition, they are featured to operate at low power consumption, allowing these devices to be supplied with small and light batteries that make possible an easy and unobtrusively wearing, enabling, at the same time, the simultaneous acquisition of biomechanical and health parameters and their routing to external (remote if it is required) systems for deeper analyses (e.g., the nearby hospital for electrocardiogram in heart disease patients) [43]. These sensitized systems developed for sports and medical applications usually feature a central unit (Master node) and a group of other nodes (the Slave nodes). The former oversees scheduling the DAQ for the whole WBAN and communicating with the user terminal, eventually hosting other sensors. The latter consists of a microcontroller unit that can handle one or more sensors in the node and the data transmission to the primary node [44]. These networks can be wired or radio-connected with the primary node for the data exchange (WSNs). These are particularly suitable in sports applications, as cables can hinder athletes' movements during training and competitions [45]. A WSN mounted on the same athlete where, by using more sensors (of the same or different type), several dynamic, kinematic, or physiological parameters are monitored is known as a Personal Area Network [46] or body sensor network [47]. The communication range represents, in this case, a particularly severe constraint where the body sensor network can cover a very short distance (Figure 2). Several wireless standardized sports protocols with different bands, data rates, transmission ranges, and network topologies are available [44]. Bluetooth, Wi-Fi, and ZigBee are wireless communication systems utilizing the Industrial, Scientific, and Medical (ISM) band [48]. However, until the early 2000s, no universal communication standard was suitable for sports and health applications developed among the leading vendors (Advanced and Adaptive Network Technology--ANT+) [49]. More recently, other systems based on common telecommunication standard protocols, such as ZigBee and Bluetooth, have been developed and put on the market. They can be effectively employed in low-power, low-bandwidth wireless mesh networking. Zigbee exploits the mesh network for data transmission over long distances by performing \"hops\" of the messages on intermediary radio nodes on the way to their destination [50]. Several systems on the market nowadays employ sensor networks based on these transmission protocols. Among the others is the Captiks system (further explored in Section 7.2), while, in [50], it is described as a sensor network based on ZigBee and designed for remote sports injury monitoring. In particular, the wireless nodes have a three-axial acceleration sensor to construct the human motion model exploiting a fifteen rigid bodies  
Figure 2: Example of a body sensor network. model. Because of the limited number of nodes placed relatively close to one other, it does not require using typical routing characteristics of such a standard to improve transmission efficiency. Ref. [51] presents a wearable wireless system designed to implement a medical IoT for patient health parameters such as the electrocardiogram (ECG), temperature, blood pressure, and blood glucose monitoring. Nowadays, there is fast growth in consumer portable devices in most daily activities, and remarkably, they have overcome the diffusion of these standards, such as ANT+ and ZigBee, since their communication protocols consist of Bluetooth and Wi-Fi only. As a result, the number of smartphone apps suited for connection with sports instrument equipment continues to grow.