A Pilot Study on the e-Kayak System: A Wireless DAQ Suited for Performance Analysis in Flatwater Sprint Kayaks

Nowadays, in modern elite sport, the identi cation of the best training strategies which are useful in obtaining improvements during competitions requires an accurate measure of the physiologic and biomechanical parameters that a ect performance. The goal of this pilot study was to investigate the capabilities of thee-Kayaksystem, a multichannel digital acquisition system speci cally tailored for atwater sprint kayaking application.e-Kayakallows the synchronous measure of all the parameters involved in kayak propulsion, both dynamic (including forces acting on the paddle and footrest) and kinematic (including stroke frequency, displacement, velocity, acceleration, roll, yaw, and pitch of the boat). After a detailed description of the system, we investigate its capability in supporting coaches to evaluate the performance of elite athletes' trough-speci c measurements. This approach allows for a better understanding of the paddler's motion and the relevant e ects on kayak behavior. The system allows the coach to carry out a wide study of kayak propulsion highlighting, and, at the same time, the occurrences of speci c technical aws in the paddling technique. In order to evaluate the correctness of the measurement results acquired in this pilot study, these results were compared with others which are available in the literature and which were obtained from subjects with similar characteristics. Keywords:sport; biomechanics; DAQ systems; paddling; atwater sprint kayaking 1. Introduction Nowadays,

same time, the occurrences of speci c technical aws in the paddling technique. In order to evaluate the correctness of the measurement results acquired in this pilot study, these results were compared with others which are available in the literature and which were obtained from subjects with similar characteristics. Keywords:sport; biomechanics; DAQ systems; paddling; atwater sprint kayaking 1. Introduction Nowadays, the use of a simple chronometer or of video analysis no longer represents a suitable system for the assessment of training or a race performance for elite athletes. Indeed, this approach does not allow for investigation of all the parameters involved in the assessment of performance, and it permits qualitative analysis at best. Conversely, a deep “knowledge of performance” by both coach and athlete (i.e., not only the value of the result itself but the way in which this has been obtained [1]) represents a key factor in improving the training procedures of this class of athletes. For this reason, it is possible to obtain better improvements in performance only when athletes and coaches are able to receive live and accurate feedback during training sessions, or an easily understandable full report after training, for deeper analysis. Sensors2020,20, 542; doi:10.3390 /s20020542 /journal/sensors

Sensors2020,20, 542 2 of 17 In recent years, several electronic measurement systems specially designed for sport applications have been proposed in the literature or have been made available on the market. With this in mind, there are some “golden rules" that must be taken into account in order to design a suitable electronic system for the monitoring of a sport performance. Firstly, the system has to be accepted by both coach and athlete. Thus, the system has to be reliable and easy to use, and its output must be easy to understand and able to allow for a deep investigation into the quality of the performance. Furthermore, to be easily accepted by the athlete, the sensors applied on him or her or on the sports equipment must be light, unobtrusive, and not liable to in uence in any way, physical or psychological, the performance itself [2–5]. In atwater sprint kayaking, an e ective paddling technique together with good physiological power and a smart race strategy plays a signi cant role in reaching peak performances among elite athletes. However, the particular features of such a paddling technique make the full comprehension of the way each force is proportionally involved in the boat's propulsion di cult [6]. Kayaking is a cyclic sport where the forces that propel the boat can be identi ed in the whole muscular kinetic chain of the athlete [7–10]. During acceleration, the athlete needs to generate propulsive forces greater than the resistive forces of air and water acting on the boat; the applied forces have to maximize the velocity and the forward acceleration, while minimizing all the other unnecessary rotations and accelerations along the axes of the boat. Furthermore, in contrast to rowing, where the oar is constrained to the hull via an oarlock, in kayaking the force transferred by the athlete to the water through the paddle during the stroke is transmitted to the boat through the body of the paddler itself via the seat and footrest [11,12]. Hence, measuring the force on the paddle or the stroke rate alone is not enough for the coach to

to the hull via an oarlock, in kayaking the force transferred by the athlete to the water through the paddle during the stroke is transmitted to the boat through the body of the paddler itself via the seat and footrest [11,12]. Hence, measuring the force on the paddle or the stroke rate alone is not enough for the coach to identify the best actions with which to improve the performances for this class of athletes. For this reason, even if the dynamic behavior of the blades in the water can be measured, the proportion with which each of these forces contributes to the boat's motion is widely debated and, consequently, the study of its propulsion very complicated [12–14]. A useful key for good comprehension of the biomechanical parameters upon which the performance of the kayaker depends could be given by an accurate and simultaneous measure of the forces exerted by the upper body musculature on the paddle and those applied by the legs on the footrest together with the kinematics of the boat. This means that an in-depth study of dynamic and kinematic parameters of both athlete and boat could allow the coach to give practical tips which will re ne the paddling technique and help to avoid speci c technical aws. In recent years, several studies [10–21] have been published on force–time curve development performed by kayakers on ergometers (non-speci c conditions), in lab measurements, and on boats (speci c race conditions). These papers (Table) describe the use of particular digital acquisition (DAQ) systems, with sensors applied on the boat either on the boat paddle or on the footrest. The table provides a brief description of each system together with information about the presence of kinematic or dynamic sensors and the capability of each system to operate under standard training conditions (on water). Speci cally, in 2009 Mickael Begon et al. [7] presented a kinematic analysis of the anteroposterior forces applied to the footrest, the seat, and the paddle of a kayak by using a special ergometer instrumented with seven uniaxial force sensors and two goniometers. The ergometer was

and the capability of each system to operate under standard training conditions (on water). Speci cally, in 2009 Mickael Begon et al. [7] presented a kinematic analysis of the anteroposterior forces applied to the footrest, the seat, and the paddle of a kayak by using a special ergometer instrumented with seven uniaxial force sensors and two goniometers. The ergometer was provided with a trolley sliding forward and backward along a static frame. The aim of this study was the assessment of the paddling performances, the analysis of the involved forces, and the coordination between the left and right sides. F. Nates et al. (2015) [20] presented a study in which, by using a special kayak ergometer (the Poitiers-B kayak ergometer), they installed six degree of freedom (DOF) force sensors for the measurement of the contact force between the athlete's hands and the paddle shaft. This allowed for a tridimensional study of the forces applied on the paddle and improvement of the knowledge in both the drive and recovery phases.

Sensors2020,20, 542 3 of 17 Table 1. State of the art on DAQ systems developed for kayaking Legend: Dyn, dynamic; Kin, kinematic. Authors Brief Description Dyn Kin On Water Vos, J.A. et al. (1974) [7] Strain gauges installed on both the paddle and footrest. A telemetry system allowed data transmission to a computer located at the shore. The study, initially formulated for rowing, has been applied to kayaking. Yes No Yes Campagna, P.D. et al. (1986) [15] One of the rst examples of an instrumented ergometer for kayaking. It has been demonstrated that this system is able to replicate open water paddling action very closely. No Yes No Aitken et al. (1992) [8] Four strain gauges are attached near each blade for the measurement of the shaft bending. A data recorder system provides memorization of the acquired data for an o ine download. Yes No Yes Pelham et al. (1993) [16] Accelerometry measurement system based on electromagnetic force–balance accelerometers. No Yes Yes Begon, M., et al. (2009) [17] Instrumented kayak ergometer for the measurement of the contact forces between the athlete and the ergometer. Yes Yes No Limonta, E. et al. (2010) [18] Kayak simulator based on an automatic motion analysis system. It performs a three-dimensional kinematic analysis of the paddler's movements. No Yes No Sturm, D. et al. (2010) [19] A wireless (Bluetooth)-based sensor system is able to perform the measurement of the paddle bending by using four strain gauges. The measurement of the pressure of the foot on a custom-built footrest is obtained by force-sensitive resistor (FSR) sensors. Yes No Yes Gomes, B. et al. (2011) [6] TheFPaddlesystem measures the strain on the shaft via two couples of strain gages, with one placed on the bending plane of the blade and the other on a perpendicular plane. A wireless system provides the data transmission. Yes No Yes Gomes, B. et al. (2015) [13] AnFPaddlesystem instrumented with two strain gauges is integrated with a triaxial accelerometer placed inside the boat. Yes Yes Yes Nates, F.M. et al. (2015) [20] A special kayak ergometer is designed with six degree of

the blade and the other on a perpendicular plane. A wireless system provides the data transmission. Yes No Yes Gomes, B. et al. (2015) [13] AnFPaddlesystem instrumented with two strain gauges is integrated with a triaxial accelerometer placed inside the boat. Yes Yes Yes Nates, F.M. et al. (2015) [20] A special kayak ergometer is designed with six degree of freedom (DOF) force sensors for the measurement of the contact force between the athlete's hands and the paddle shaft. Yes No No Luo Niu et al. (2019) [21] The measurement of the force on the shaft is obtained by the use of Fiber Bragg Grating (FBG) optical ber sensors enclosed in the material of the blades. Yes Yes No In 2010, Sturm et al. [19] were involved in the design of a system consisting of force sensors positioned on both the paddle and footrest and wirelessly connected to a central unit via a Bluetooth radio link. The goal of this study was to present a measuring tool able to record, in a training session of atwater kayaking, the strength on the paddle and footrest. The forces on the paddle were measured by means of four strain gauges connected in a Wheatstone full-bridge, while, for the measure of the forces on the footrest, force-sensitive resistor (FSR) sensors were employed. The measures obtained by the proposed system were compared to those achieved using a Dansprint kayak ergometer [22], showing a good correlation between the power (measured by the ergometer) and the force on the paddles (measured by sensors). In 2011, Gomes et al. [14] investigated the intracyclic velocity variation as well as the kayak's motion using a triaxial accelerometer in K1, K2, and K4 boats. In the same year, Gomes et al. [6] presented theFPaddlesystem. This is a wireless system that allows the measurement of the paddle forces in a speci c environment. Later, in 2015, the same authors presented an updated version of the FPaddlesystem (with only two strain gages) where the paddling force pro le and the force–time curves were studied together with triaxial accelerometry [13].

[6] presented theFPaddlesystem. This is a wireless system that allows the measurement of the paddle forces in a speci c environment. Later, in 2015, the same authors presented an updated version of the FPaddlesystem (with only two strain gages) where the paddling force pro le and the force–time curves were studied together with triaxial accelerometry [13].

Sensors2020,20, 542 4 of 17 Finally, Luo Niu et al. (2019) [21] proposed to evaluate kayak paddling performance by use of a custom-built paddle instrumented with a special optical ber technology, namely, Fiber Bragg Grating (FBG) strain sensors [23]). Through this new technology system, it is possible to measure handgrip load and blade load distribution in on-water kayaking in real time. The proposed technology seems to be very promising for the measurements of forces on the paddle. Nevertheless, it seems to be obtrusive (it is still a cabled system) and it cannot be employed in standard training conditions. In fact, the presence of the cables does not allow for a speci c assessment of the performance [3,19]. In kayaking, the main kinematic parameters which are useful in the investigation of performance include velocity, acceleration, intra-cyclic velocity, roll, and pitch of the boat. In addition, the dynamic parameters have to include stroke frequency, forces acting on the paddle and footrest, the symmetry between the forces on the right and left side for both the paddle and footrest, and the synchronization among these forces [12–14]. As previously shown, most of these systems cannot simultaneously measure the kinematic and dynamic parameters that a ects the kayaker's performance. In particular, as reported in Table, only three of them are able to obtain both measurements, and, among these, only one has been designed for on-water use [13]. In this context, the aim of this pilot study was to investigate the capabilities of a wireless multichannel portable DAQ (thee-Kayaksystem) in supporting coaches to evaluate the performance of elite athletes. The system is tested on a couple of athletes through speci c measurements during on-water training and simulating speci c race phases in a speci c atwater kayak environment. In particular, the measurement results presented in this paper are related to some di erent tests, i.e., a slow-pace test (100 m and 150 m for the female and male subjects, respectively), a 50 m fast-pace test for the female subjects only, and, for the male subjects, a 40 m speed test simulation starting from the race blocks.

kayak environment. In particular, the measurement results presented in this paper are related to some di erent tests, i.e., a slow-pace test (100 m and 150 m for the female and male subjects, respectively), a 50 m fast-pace test for the female subjects only, and, for the male subjects, a 40 m speed test simulation starting from the race blocks. In the slow-pace tests, the subjects are asked by the coach to perform the test with care taken to perform the proper paddling technique (i.e., performing a speci c work on the technical gesture). The tests are carried out in a lake with a negligible level of water currents, and the system synchronously acquires the force signal on both the paddle and footrest, the position and the boat's speed by a Global Position System (GPS) device and three-axis acceleration, and the yaw, pitch, and roll by an inertial measurement unit (IMU) installed inside the boat. The goal of the test was the evaluation of the type of parameters supplied by it in order to verify their usefulness for the measurement of the performance and the identi cation of technical aws. Moreover, the test veri es the usability of the system as per the readability of the output by the coaches and easiness of the setup and calibration procedures. 2. Materials and Methods 2.1. Measurement System The DAQ used for measurements here is the “e-Kayaksystem”, which was developed in the framework of a project carried out on behalf of the Italian Olympic Committee. We have employed a version customized for atwater sprint kayaking of the DAQuino system [24,25], a modular architecture easily customizable for particular sport application that allows for the connection of up to eight slave nodes to a master one via a high performance 2.4 GHz wireless link (ISM Band). The design of this new system was inspired by previous experience gained using a rst preliminary prototype developed in 2016 [26]. Although that prototype presented the same class of sensors (IMU, GPS, and force sensors) of the DAQuino system, the modular architecture, the maximum available sample rate of most

one via a high performance 2.4 GHz wireless link (ISM Band). The design of this new system was inspired by previous experience gained using a rst preliminary prototype developed in 2016 [26]. Although that prototype presented the same class of sensors (IMU, GPS, and force sensors) of the DAQuino system, the modular architecture, the maximum available sample rate of most of the new employed sensors, the unobtrusiveness in the position of the force sensors, and the new implemented communication protocol make the new system more reliable and e ective. For example, in the previous prototype system, the slave node for the measurement of the force exerted on the paddle was installed on the outside in the middle of the shaft (a barycentric but rather obtrusive position) while the connection with the footrest was implemented by a wire. Furthermore, in a manner

Sensors2020,20, 542 5 of 17 di erent from the previous system, the modular architecture of the new system easily allows its use on K2 and K4 boats. In particular, the new system is equipped with a 9-axis IMU, a high sample rate GPS device, and a pair of force sensors applied on the paddle and footrest for each of the kayakers belonging to the crew of the boat. Hence, as depicted in Figure, the system designed for a K1 boat (i.e., a kayak with only one paddler) presented in this paper is composed of a master node (M) and two slave nodes equipped with force sensors and installed on the paddle (S1) and footrest (S2).Sensors 2019, 19, x FOR PEER REVIEW 5 of 16 Figure 1. Block scheme of the e-Kayak system. Legend: GPS, Global Positioning System; IMU, inertial measurement unit; S1, paddle; S2, footrest. Since the interface is a webpage, it can be used with any operating system and any device, as long as a web browser is present. In addition, the master node manages the synchronization of the data acquisition; due to the large amount of computational resources needed to carry out all these tasks, the node has been designed to host a high-performance micro controller unit (MCU, 32 bit 180 MHz ARM Cortex-M4 Pjrc’s Teensy 3.6). The wi-fi transmission is based on the module ESP8266 (Espressif Systems Co., Ltd., Shanghai, China), while the communication with the slave nodes is granted by nRF24L01P+ modules (Nordic Semiconductor [27]). These modules are low power single chip transceivers in the global license-free 2.4 GHz ISM band with high-speed communications capability (up to 2 Mbit/s). They are suitable for deploying wireless networks in several application fields. In the e-Kayak system, they have been equipped with an external antenna that increases the transmission range of the device in order to overcome the signal losses due to the boat and the body of the athlete itself. The GPS device which is installed in the system is based on the Venus822A chip by Skytraq Technology Inc. Taiwan. It has been designed for quad-GNSS (Global Navigation

The study evaluates a wireless DAQ system for performance analysis in kayaking.