Aspectos cuantitativos del abandono en Tenerife

2.4.1 Considerations in measurement device selection

For research purposes and clinical application, measurement device selection should be dictated by the particular aspect of wheelchair mobility under investigation (Wilson et al., 2008). Conger et al. (2014) developed a model for prediction of EE based on power output, HR and movement speed using a modified PowerTap track hub. While the prediction model was strong (r2 = 0.87), considerable modifications need to be made to the wheel to accommodate the device. Further, device weight is considerable (460 g). Therefore, application for measurement is questionable in a sport such as wheelchair tennis, which requires considerable agility (i.e. turning, braking and changes in movement direction) for adequate court-coverage.

2.4.2 Methods for determination of court-movement and associated limitations

Accelerometers have been used for the collection of wheelchair propulsion movement data variables. Wheel orientation is indicated by measurements of acceleration taken along two perpendicular axes in the plane of the wheel. Therefore, with wheel rotation, measures of distance and speed can be obtained. The activePAL accelerometer (PAL Technologies, Glasgow, UK) has been adapted for collection of wheelchair mobility data, with good functional applicability for collection of distance and speed in a free-living environment (Wilson et al., 2008). The device offers an accurate and reliable assessment of wheel revolutions, absolute angle and duration of movement for subsequent calculation of distance and speed (Coulter et al., 2011). However, convenience samples have been used (Wilson et al., 2008), with small numbers of individuals with SCI operating at very low to low speeds (~1 m·s-

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) (Sonenblum et al., 2012; Coulter et al., 2011; Wilson et al., 2008). Such a device is likely to be suitable for monitoring of everyday propulsion trends over long periods, and for conditions where the terrain is non-uniform. However, high frequencies of wheel rotation exceeding plausible angular wheel rotations may be rejected (Sonenblum et al., 2012). More recently, the inertial movement unit (IMU) has become an option for court-movement monitoring. Devices, which are lightweight (~ 10 g) and have small dimensions, include a gyroscope alongside an accelerometer for instantaneous assessment of position, orientation and velocity. Acceptable validity and reliability for IMU have been revealed at speeds consistent with wheelchair court- sports activity (1.0 to 6.0 m·s-1) (Mason et al., 2014b). However, as a motorised treadmill was used for linear motion, ecological validity, which is an important benchmark for wheelchair

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sports-specific testing (Goosey-Tolfrey & Leicht, 2013), cannot be assured for wheelchair tennis. Consideration has been given to IMU performance during wheelchair basketball with minimal error for frame displacement and speed, including rotational speeds (van der Slikke et al., 2015). This is encouraging given that an important aspect of performance in the court-sports is the turning action (Mason et al., 2010). However, play was simulated (i.e. series of drills), a relatively low-cost reference system was used, and proportionately higher (but acceptable) error rates for high speed movements were obtained.

Movement during sports are much higher than those observed in the accelerometer studies, with wheelchair racers known to attain speeds > 5 m·s-1 (Campbell et al., 1995). Comparatively lower mean speeds are expected in the wheelchair court sports (i.e. basketball, rugby and tennis), as players navigate around a smaller area in a non-linear manner. However, speeds > 1 m·s-1 should most certainly be expected. Peak speeds ranging from 2.99 ± 0.28 to 3.82 ± 0.31 m∙s-1

have been reported for wheelchair rugby players with varying playing roles and positions (Rhodes et al., 2014) and average speeds of 1.26 m∙s-1 (Mason et al., 2014a). As stated previously, surface conditions are an influencing factor in AB tennis (Reid et al., 2013; Martin et al., 2011) and while it is not known currently, the same may be true for wheelchair tennis. However, most often, court-based sports events and tournaments are held on hard surfaces and hence, devices validated for use on uneven terrain are not required. Also, events are mostly held in an indoor environment, precluding some mainstream devices (i.e. GPS). Collectively, these observations suggest a preference for movement logging technologies which have greater applicability, and appropriateness for, the natural sporting environment.

The telemetry-based velocometer is placed on the wheel and provides velocity (Moss et al., 2003) but is most likely limited to research-based testing (Goosey-Tolfrey et al., 2012) due to its considerable mass, time-consuming calibration and fitment. Given that complex movement requirements are associated with wheelchair tennis (Diaper & Goosey-Tolfrey, 2009), chair- borne recording devices need to be light, small, and suitably accurate to be useful. However, most cannot be configured easily in this way, giving rise to the popularity of tracking methods external to the chair. Distance, average velocity and direction have been collected using a video tracking method in wheelchair rugby (Sarro et al., 2010) and previously for ambulant sports like soccer (Barros et al., 2007). More recently, a radio-frequency based tracking system has been used to good effect in wheelchair rugby (Rhodes et al., 2015b; Mason et al., 2014a), with validity and reliability confirmed (Rhodes et al., 2015a). However, the time consuming set-up and calibration processes may preclude use of tracking systems in scenarios where a more expedient approach is required, for example, during tennis tournaments whereby players are required to move between courts. Also, tracking systems can only be used indoors which limits

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their applicability for tennis. In contrast, DL and GPS units are relatively easy to place on the chair or body respectively with minimal invasiveness and are lightweight and portable. However, neither device has been tested for wheelchair tennis applicability. As there appears to be no consensus regarding the most appropriate device for quantification of court-movement, scrutiny of the most common, portable and lightweight measurement devices for wheelchair tennis is merited.