Reference: AJ Wixted, DC Billing, DA James, Validation of Trunk Mounted Inertial Sensors for Analysing Running Biomechanics under field conditions, using synchronously collected foot contact data, Sports Engineering 12 (4), 207-212 Abstract: The biomechanical evaluation of elite athletes often requires the use of sophisticated laboratory-based equipment that is restrictive, cumbersome, and often unsuitable for use in a training and competition environment. Small, low-mass unobtrusive centre-of-mass triaxial accelerometers can be used to collect data but may not reveal all the information of interest. This validation of centre-of-mass triaxial accelerometry uses previously reported synchronously collected foot-contact information from in-shoe pressure sensors. A qualitative assessment of the system output indicates that the centre-of-mass acceleration provides valuable insight into the use of accelerometers for investigating the biomechanics of, in this case, middle distance runners. Results: A notable result was the absence in the acceleration data of any significant curve running versus straight running identifying signature, in either the extracted orientation data or the dynamic running data. This is demonstrated in Figs. 2 and 3 where the six traces for the race sample points cluster together making the data for each sensor appear as either a thick dark line or a tightly interwoven mix of lines. The signals for each acceleration axis and the in-sole sensors maintained an ongoing consistency across the sampled race points. The left hallux in-sole pressure increased during running on the curve (for both athletes).  Fig. 2 Subject A, comparison of representative accelerometer and in-sole pressure data from six race points
 Fig. 3 Subject B, comparison of representative accelerometer and in-sole pressure data from six race points Comparing in-sole pressure of subject A (Fig. 2) with subject B (Fig. 3) showed that subject A had a relatively small heel strike, with the majority of the pressure initially occurring on the third MTH sensor and then moving to the first MTH sensor and finally to the hallux sensor. Subject B had a comparatively large heel pressure with the pressure then moving to the third and first MTH sensors. Relative to the first MTH pressure the hallux pressure was quite small. This suggested that subject A landed with a flatter foot contact and then rolled forward to give the bulk of the final propulsion from a combination of the area around the first MTH and hallux. Subject B landed with the heel striking first and then obtained maximum pressure from the area of the first and third MTHs (1st MTH area predominated). When comparing the in-sole signal to the accelerometer signal, the anterior–posterior acceleration had a significant negative phase (braking) occurring at approximately the same time as the heel strike. This occurred for both athletes but was far more noticeable for subject B, who also had the much larger heel pressure. For both athletes the vertical acceleration went to zero at approximately the same time as foot contact ceased. Separate data collected from a subject on a treadmill showed the toe-off point moving as a function of speed, with the toe-off occurring later with respect to the acceleration data zero crossing as running speed decreased. For these athletes, the orientation of the sensor extracted from the low-pass filter was reasonably stable for the duration of the race. For subject A, the rotation about the AP axis (sideways tilting) was\1.5. and the forward lean of the sensor was \3.. For subject B the corresponding values were\1. and around 11.. For subject B these values made a noticeable difference in the relative size of the peak V and AP acceleration during contact when comparing the rotated acceleration (Fig. 3) and the un-rotated acceleration (Fig. 4).  Fig. 4 Subject B, un-rotated accelerometer data corresponding to Fig. 3 Conclusion: Although this note only gives a brief qualitative analysis of the collected data, it appeared that the in-shoe pressure sensors allowed the framing of the triaxial centre-of-mass accelerometry such that the accelerometry could be used on its own to provide useful insight into the running technique of an athlete. The initial foot contact and final contact appeared to be discernable in the acceleration data, as did the effective application of contact forces. References: 1. Auvinet B, Gloria E, Renault G, Barrey E (2002) Runner’s stride analysis: comparison of kinematic and kinetic analyses under field conditions. Sci Sports 17(2):92–94 2. Barrey E, Evans SE, Evans DL, Curtis RA, Quinton R, Rose RJ (2001) Locomotion evaluation for racing in thoroughbreds. Equine Vet J Suppl 33:99–103 3. Hennig EM, Milani TL (1995) In-shoe pressure distribution for running in various types of footwear. J Appl Biomech 11(3):299– 310 4. Billing DC, Hayes JP, Harvey EC, Baker J (2004) Measurement of ground reaction forces using unobtrusive, on-athlete instrumentation.In: Proceedings of the IEEE international conference on intelligent sensing and information processing (ICISIP 2004), Chennai, India, 04–07 January 2004, pp 218–221 5. Billing DC, Nagarajah CR, Hayes JP, Baker J (2006) Predicting ground reaction forces in running using micro-sensors and neural networks. Sports Eng 9(1):15–27 6. Lee JB, Burkett B, Mellifony RB, James DA (2007) The use of MEMS technology to assess gait characteristics. In: Fuss FK, Subic A, Ujihashi S (eds) The impact of technology on sport II. Proceedings of the 3rd Asia Pacific congress on sports technology, Singapore, 23–26 September 2007, pp 181–186 7. James DA, Davey N, Gourdeas L (2003) A modular integrated platform for microsensor applications. In: Proceedings of SPIE’s international symposium on microelectronics, MEMS, and nanotechnology, Perth, Australia, 10–12 December 2003, vol 5274, pp 371–378 8. Lai A, James DA, Hayes JP, Harvey EC (2003) Semi-automatic calibration technique using six inertial frames of reference. In: Proceedings of SPIE’s international symposium on microelectronics, MEMS, and nanotechnology, Perth, Australia, 10–12 December 2003, vol 5274, pp 531–542 9. Parotec System Instruction Manual (1997) Paromed Medizintechnik GmbH. Neubeuern, Germany 212 |
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