Accuracy and speed are related to performance in tennis. Most research has focused on speed and little is known about the probabilistic structure of error (i.e. accuracy). In the present study 31 advanced players performed a standardised test and accuracy was measured using video analysis. Parameters describing 95% confidence ellipses (CEs) of forehand and backhand were calculated to determine the probabilistic structure of errors. Results showed that for both groundstrokes the long axis of the CEs was oriented almost parallel to the sideline. Despite greater ball speed (~107.2 vs. ~97.3 m • s⁻¹; p < 0.001), the forehand showed a smaller longitudinal distance to the target than the backhand (~123.3 vs. ~164.0 cm; p = 0.024) and a smaller CE area (~34.4 vs. ~40.3 m²; p = 0.045). This means that tennis shot placements fit a bivariate normal distribution (represented by an ellipse), similar to other throwing sports, with differences between the forehand and backhand. Further research will need to explore the underlying causes of these distributions, which in turn may open up opportunities for coaches to modify them in their players according to what is deemed most vital for improved performance.

Chest bands have been the most used device to monitor heart rate during running. However, some runners feel uncomfortable with the use of bands due to the friction and pressure exerted on the chest. Thus, the aim of this study was to determine if the photoplethysmography (PPG) system Polar Precision Prime used in the Polar Vantage M watch could replace chest bands (Polar V800-H10) to monitor heart rate with the same precision. A group of 37 people, middle-distance and long-distance professional runners, participated in this study. The submaximal speed was determined using 50% of the participants’ maximum speed in the height of their season. The Polar Vantage M reported high correlation (r > 0.84) and high ICC (ICC > 0.86) when comparing its heart rate monitor with the Polar V800 synchronised with H10 chest strap during recording intervals of more than 2 min. The systematic bias and random error were very small (<1 bpm), especially for the 600 s recording interval (0.26 ± 5.10 bpm). Nevertheless, the error increased for 10 s (−5.13 ± 9.20 bpm), 20 s (−8.65 ± 12.60 bpm) and 30 s (−10.71 ± 14.99 bpm) time intervals. In conclusion, the PPG Polar Precision Prime included in the Polar Vantage M demonstrates that it could be a valid alternative to chest bands for monitoring heart rate while running, taking into account some usage considerations, good strap adjustment and an initial calibration time during the first 2–3 min.

Optoelectronic motion capture systems are considered the gold standard for measuring walking and running kinematics parameters. However, these systems prerequisites are not feasible for practitioners as they entail a laboratory environment and time to process and calculate the data. Therefore, this study aims to evaluate the validity of the three-sensor RunScribe Sacral Gait Lab™ inertial measurement unit (IMU) in measuring pelvic kinematics in terms of vertical oscillation, tilt, obliquity, rotational range of motion, and the maximum angular rates during walking and running on a treadmill. Pelvic kinematic parameters were measured simultaneously using an eight-camera motion analysis system (Qualisys Medical AB, GÖTEBORG, Sweden) and the three-sensor RunScribe Sacral Gait Lab™ (Scribe Lab. Inc. San Francisco, CA, USA) in a sample of 16 healthy young adults. An acceptable level of agreement was considered if the following criteria were met: low bias and SEE ( 0.90), and good reliability (ICC > 0.81). The results obtained reveal that the three-sensor RunScribe Sacral Gait Lab™ IMU did not reach the validity criteria established for any of the variables and velocities tested. The results obtained therefore show significant differences between the systems for the pelvic kinematic parameters measured during both walking and running.

The use of markerless motion capture systems is becoming more popular for walking and running analysis given their user-friendliness and their time efficiency but in some cases their validity is uncertain. Here, the test-retest reliability of the MotionMetrix software combined with the use of Kinect sensors is tested with 24 healthy volunteers for walking (at 5 km·h⁻¹) and running (at 10 and 15 km·h⁻¹) gait analysis in two different trials. All the parameters given by the MotionMetrix software for both walking and running gait analysis are tested in terms of reliability. No significant differences (p > 0.05) were found for walking gait parameters between both trials except for the phases of loading response and double support, and the spatiotemporal parameters of step length and step frequency. Additionally, all the parameters exhibit acceptable reliability (CV < 10%) but step width (CV > 10%). When analyzing running gait, although the parameters here tested exhibited different reliability values at 10 km·h⁻¹, the system provided reliable measurements for most of the kinematic and kinetic parameters (CV < 10%) when running at 15 km·h⁻¹. Overall, the results obtained show that, although some variables must be interpreted with caution, the Kinect + MotionMetrix system may be useful for walking and running gait analysis. Nevertheless, the validity still needs to be determined against a gold standard system to fully trust this technology and software combination.

Photoplethysmography (PPG) heart rate devices are greatly affected by the motion artifacts of running. As a result, their application in training load systems and effort control strategies based on heart rate (HR) could be debatable. In 2019, Polar applied some new features on their PPG devices to improve their accuracy. Thus, the purpose of this study was to determine the level of agreement between the new PPG system Polar Precision Prime™ and the chest strap Polar H10 (reference system) in the HR monitoring during an interval running protocol. A group of 37 long distance runners completed an interval running protocol of 10 min composed of five 1-min trials with an active break of 1-min between each trial. An excellent reliability (ICC > 0.9) was obtained for the entire interval running protocol with the lowest values in the first 2 min (ICC = 0.960–0.949), slight differences between intensities (ICC = 0.992–0.986), and a reduction of the observed tendency (ICC > 0.9) when the Edwards quantification model was applied (ICC = 0.877–0.967). The Bland-Altman plots with the final HR values of each trial establish a systematic bias (<1 bpm) for all intervals with a random error (<4 bpm), except in the first trial which had a higher random error (6.85 bpm). In conclusion, the innovations applied in the new PPG system provide the accuracy required for use in diverse functions, including endurance running.

The biomechanics of walking and running, in both ground and treadmill conditions, have been extensively analysed and important differences have been reported. Despite some previous studies having examined the validity and reliability of the OptoGait™ system for measuring gait characteristics during walking, no previous works have determined the reliability and validity of this system while running on a treadmill. Therefore, this study aimed to determine the absolute reliability (within-subject variation) and evaluate the concurrent validity of the OptoGait™ system for measuring spatiotemporal variables while running at a comfortable speed by comparing data with a highly accurate system of measuring those parameters (i.e. video analysis at 1000 Hz). Forty-nine endurance runners performed a running protocol on a treadmill at a comfortable speed. Two systems were used to collect data: OptoGait™ system and high-speed video analysis at 1000 Hz. The coefficient of variation (CV) was calculated as a measure of absolute reliability. The OptoGait™ system reported a CV range between 2.2% and 11.4% for spatiotemporal parameters, while the video analysis showed a CV range between 0.02% and 9.9%. To determine concurrent validity, intra class correlation coefficients (ICC) and pairwise comparisons of means (t-test) were calculated between data from both systems. Although the paired t-test demonstrated significant differences between systems, a high level of agreement (ICC > 0.89) was obtained in spatiotemporal parameters between systems. When compared to a high-speed video analysis at 1000 Hz, the results indicate that the OptoGait™ system is a reliable and valid tool to measure spatiotemporal gait characteristics while running on a treadmill at a comfortable speed.