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11:30   Measurements for motion analysis Chair: Anoek van Vlaardingen 11:30 20 mins STABILITY OF ACCELEROMETRIC INDICATORS MEASURED WHILE RUNNING Thomas Provot, Marcela Munera, Fabrice Bolaers, Grégoire Vitry, Xavier Chiementin Abstract: ABSTRACT Recently the use of Inertial Measurement Units (IMU’s) has been extended to several applications in human activity. In running, several studies show the possibility of using IMU’s to measure the speed (Yang, Mohr, & Li, 2011), the stride, step, stance duration (J. B. Lee, Mellifont, & Burkett, 2010) (Y.-S. Lee et al., 2015) (Henriksen, Lund, Moe-Nilssen, Bliddal, & Danneskiod-Samsøe, 2004) and to determine the foot strike pattern (Giandolini et al., 2014). However, there is not studies that describe the stability of those indicators. In this context, the aim of this study is to analyse the intra and inter test stability of several accelerometric indicators using an IMU under constant running conditions. For one subject, accelerations are measured using two IMU’s (Hikob Fox, sampling frequency: 1344 Hz) mounted on the right tibia and the dorsal surface of the shoe above the metatarsals. The subject (age: 22 years; height: 173 cm; weight: 76 kg) follows two different protocols containing 10 measures of 1 minute running on a treadmill at 12 km/h with 1 minute rest between measures. In the first test the intra test stability is analysed. In the second, the IMU’s were removed and reinstalled on the subject during time of rest to analyse the intra test stability. Using the acceleration signals eight parameters were computed. Two parameters in the temporal domain: acceleration root mean square (RMS) values and Kurtosis giving indication of the input acceleration and shock. Two parameters in the frequency domain: total energy and median frequency indicating the level of excitation and the range of frequencies excited during the activity. And four parameters associated to the stride: mean maximal peak and the durations of stride, step, and stance, as reported in literature. For all parameters the mean, standard deviation and coefficient of variation were computed for each set of test. The coefficient of variation was lower than 10% for both test for all parameters except the Kurtosis and the median frequency. Those parameters doesn’t present a stable value at constant conditions of surface and speed, they cannot be used an indicator to compare several conditions. These results show several indicators that have a stable measure using IMU and could lead to studies of the influence of the speed, the surface or the anthropometry of the subjects. Acknowledgements These investigations are financially supported by the Champagne-Ardenne region and by The European Found of Regional Development (FEDER). The authors wish to thank neXXtep Technologies for their contribution. References Giandolini, M., Poupard, T., Gimenez, P., Horvais, N., Millet, G. Y., Morin, J.-B., & Samozino, P. (2014). A simple field method to identify foot strike pattern during running. Journal of Biomechanics, 1–6. Henriksen, M., Lund, H., Moe-Nilssen, R., Bliddal, H., & Danneskiod-Samsøe, B. (2004). Test-retest reliability of trunk accelerometric gait analysis. Gait and Posture, 19(3), 288–297. Lee, J. B., Mellifont, R. B., & Burkett, B. J. (2010). The use of a single inertial sensor to identify stride, step, and stance durations of running gait. Journal of Science and Medicine in Sport, 13(2), 270–273. Lee, Y.-S., Ho, C.-S., Shih, Y., Chang, S.-Y., Róbert, F. J., & Shiang, T.-Y. (2015). Assessment of walking, running, and jumping movement features by using the inertial measurement unit. Gait & Posture, 41(4), 877–881. Yang, S., Mohr, C., & Li, Q. (2011). Ambulatory running speed estimation using an inertial sensor. Gait and Posture, 34(4), 462–466. 11:50 20 mins MEASURING STRAIGHT TIME IN ELITE SHORT TRACK SPEED SKATING RELAYS Andrew Hext, Ben Heller, John Kelley, Simon Goodwill Abstract: In short track speed skating, the relay exchange provides an additional strategic component to races by allowing a team to change the skater involved in the pack race. It is thought that during this period of the race, time can be gained or lost due to the execution of the relay exchange. However, the only temporal measurement reported in short track speed skating is lap time, of which the relay exchange accounts for less than 30 %. As such, a more appropriate measurement of relay exchange performance might be the time taken to complete the straight where the relay exchange was executed. The aim of this study, therefore, was to validate a method for measuring straight time during elite short track speed skating relays. The proposed method used a single HD camcorder to create virtual timing gates at the start and end of both straights. To validate the method, straight times measured using the single HD camcorder were compared to synchronised cameras located perpendicular to the virtual timing gates. The root mean square error for both near and far straight times was less than the temporal resolution of the camera. In addition, Bland-Altman plots showed that the single HD camcorder method was invariant to race speed. Collectively, these findings suggest that a single HD camcorder does provide a valid method for measuring straight times during elite short track speed skating relays. 12:10 20 mins A NOVEL PROTOCOL TO MEASURE SHORT SPRINT PERFORMANCE Robin Healy, Michelle Norris, Ian C Kenny, Andrew J Harrison Abstract: Sprint performance is an important skill in many sports, with the ability to accelerate rapidly critical to success. A key factor in any testing protocol is the ability to reliably detect positive changes in performance that may come as a result of training or decrements in performance due to injury etc. The development of infrared dual beam photocell systems has enabled sprint times to be measured to within 0.01 s, with sprint acceleration ability frequently assessed over a five or ten metre distance. This commonly used protocol requires the athlete to start at a set distance behind the initial timing gate with timing triggered only when the infrared beams are disrupted. In this way all sprints assessed with this protocol can be considered as “flying” i.e. the athlete has developed momentum prior to the initiation of timing. Changes in performance over the initial distance therefore, cannot be detected. This paper describes a method to assess five and ten metre sprint performance whereby timing is triggered by the initial movement of the athlete through the synchronisation of dual beam timing gates and the OptojumpTM optical measuring system (Microgate, Bolzano, Italy). With this method practitioners and sport scientists can assess true five and ten metre sprint performance from a standing start.