This study aims to develop and validate an automated system for identifying skating-style cross-country subtechniques using inertial sensors. In the first experiment, the performance of a male cross-country skier was used to develop an automated identification system. In the second, eight male and seven female college cross-country skiers participated to validate the developed identification system. Each subject wore inertial sensors on both wrists and both roller skis, and a small video camera on a backpack. All subjects skied through a 3450 m roller ski course using a skating style at their maximum speed. The adopted subtechniques were identified by the automated method based on the data obtained from the sensors, as well as by visual observations from a video recording of the same ski run. The system correctly identified 6418 subtechniques from a total of 6768 cycles, which indicates an accuracy of 94.8%. The precisions of the automatic system for identifying the V1R, V1L, V2R, V2L, V2AR, and V2AL subtechniques were 87.6%, 87.0%, 97.5%, 97.8%, 92.1%, and 92.0%, respectively. Most incorrect identification cases occurred during a subtechnique identification that included a transition and turn event. Identification accuracy can be improved by separately identifying transition and turn events. This system could be used to evaluate each skier’s subtechniques in course conditions.
This study re-evaluated the magnitude of hand propulsion (HP) in the pull and push phases of the front crawl stroke and investigated the association between the angular velocity of shoulder roll (ω) and hand propulsive lift (HP). ω was computed in the plane normal to a forward direction for 16 skilled swimmers performing the front crawl stroke at a maximal sprinting pace. HP, hand propulsive drag (HP) and HP were determined by a dynamic pressure approach. HP and HP in the pull phase were greater than in the push phase (P < 0.05) while HP in the pull phase was similar to that in the push phase. Eleven swimmers out of the 16 swimmers had a significant within-swimmers correlation between ω and HP in the push phase (P < 0.05). That is, HP increased in the push phase as the ω of rolling back to the neutral position became faster. A swimmer should use more drag for hand propulsion in the pull phase and propulsion from drag and lift equally in the push phase. Based on the relationship between ω and HP in the push phase, a possible stroke technique to enhance HP using ω is discussed.
An automatic sy stem Jor evaluating the coking coals was develojled at Nippon Steel Corporation in 1974. In this system, the reflectance oj coal is measured automatically and rapidly and then converted to the coking parameters based on the coal petrographical point qf view. It takes only 30-100 min to make 2 X 10 4-1 X 10 5 measurements oj reflectance in a sample. From the measured reflectance distribution Jar the whole maceral and vitrillite alone, the coking index are comjmted. Many applications qf the automatic system Jar coal jletrograpJ~), have been developed with satisfactory results.
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