Abstract
Wearable sensor systems are a emerging tools for the evaluation of the sport’s activity and can be used to quantify the external workload of the athlete. The main goal of this paper was to evaluate the validity and reliability of the “Armbeep inertial measurement unit” (IMU) sensor both in a closed tennis exercise and in open matchplay. Twentyfour junior tennis players performed a baseline drill and played matches, during which they wore a combined accelerometer and gyroscope sensor. Video footage was concomitantly recorded using a digital video camera. The agreement between the measurements was assessed with the intraclass correlation coefficient (ICC) and the standard error of measurement (SEM). A simple linear regression was used to predict the number of shots registered from the video and from the Armbeep IMU sensor’s data. The number of total forehand and backhand shots during the drill repetitions showed an excellent test and re-test reproducibility (ICC≥0.90). There was a significant relationship between the Armbeep IMU sensor’s number of contacts and the total number of shots (R2 = 0.938) which indicated the excellent reliability of the tested Armbeep IMU sensor for those parameters. Considering the accuracy of the total tennis shots and the small magnitude of error for wrist speed and acceleration, the Armbeep IMU sensor appears to be an appropriate on-court tool that can be used to monitor the hitting load during tennis practice and matches.
Highlights
A large number of wearable devices, which measure biomechanical, physiological, and other indicators, or recognize sport specific movements of athletes are available on the market
It must be stressed that a derived parameters forehand and backhand contact penalty did not show acceptable reproducibility as 95% confidence interval for intraclass correlation coefficient (ICC) was between -0.124 and 0.836 indicating poor to moderate reproducibility, which cannot be acceptable in practice
Upon the retest all measurements were slightly higher, but repeated measures analysis of variance (ANOVA) did not show any significant differences between test and re-test (p>0.05 for all instances; Table 2)
Summary
A large number of wearable devices, which measure biomechanical, physiological, and other indicators, or recognize sport specific movements of athletes are available on the market. Wearable sports devices incorporating sensor technology most commonly include accelerometers, magnetometers, and gyroscopes, that detect and analyze the sport motor-tasks performed by athletes using inertial measurement units (IMU). Wearable sensors are increasingly used to measure external load, which is defined as the amount of work performed by an athlete that is measured independently of his or her internal. The external load is represented by running speed and distance traveled as well as shot number, speed, and tempo in a given time unit [3]. The assessment of internal training load requires quantification of the intensity and duration of the physiological stress imposed on the athlete [5]. Several methods are used to determine internal training load: heart rate (HR), maximal oxygen consumption (VO2max), training impulse (TRIMP), lactate concentrations, as well as biochemical, hormonal, or immunological assessments [6]
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