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Smoothing to obtain accurate position and velocity data near impacts in sport biomechanics studies is complicated by the accelerations of impact, endpoint effects and the smoothing technique used. Wrist goniometric data with two levels of random noise added were used to examine three endpoint modelling conditions for obtaining accurate position and velocity data at impact in the tennis forehand. The common approach of smoothing through impact created distortions of the position signal up to 100 ms before impact and resulted in consistent underestimations (-3.2%) of wrist angle and angular velocity (-67.9%) at impact. New linear and polynomial extrapolation conditions smoothed with all techniques provided lower root mean squared errors than the smoothing-through-impact condition, with discrete wrist positions at impact within 1.1% of the criterion data. Both the new linear and polynomial conditions can be used to make more accurate angular position and velocity estimates for tennis impacts, whereas the smoothing-through-impact condition creates spurious decreases in speed before impact that in the past have been assumed to be aspects of skilful movement. 相似文献
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Smoothing to obtain accurate position and velocity data near impacts in sport biomechanics studies is complicated by the accelerations of impact, endpoint effects and the smoothing technique used. Wrist goniometric data with two levels of random noise added were used to examine three endpoint modelling conditions for obtaining accurate position and velocity data at impact in the tennis forehand. The common approach of smoothing through impact created distortions of the position signal up to 100 ms before impact and resulted in consistent underestimations (-3.2%) of wrist angle and angular velocity (-67.9%) at impact. New linear and polynomial extrapolation conditions smoothed with all techniques provided lower root mean squared errors than the smoothing-through-impact condition, with discrete wrist positions at impact within 1.1% of the criterion data. Both the new linear and polynomial conditions can be used to make more accurate angular position and velocity estimates for tennis impacts, whereas the smoothing-through-impact condition creates spurious decreases in speed before impact that in the past have been assumed to be aspects of skillful movement. 相似文献
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基于AT89C51的单片机综合实验设计 总被引：1，自引：0，他引：1
采用AT89C51单片机为核心，通过其串行口接收来自温度传感器的数据以探测室内温度，并由其P1．1口输出信号控制继电器通断，由继电器进一步控制加热器通断，从而构成“室温自动控制系统”并设计成综合实验，使学生对51系列单片机应用系统的开发方法有更为全面的理解。 相似文献
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Changes in angular momentum during the tennis serve 总被引：1，自引：0，他引：1
Bahamonde RE 《Journal of sports sciences》2000,18(8):579-592
Three-dimensional cinematography and the direct linear transformation method were used to obtain the coordinates of the landmarks of five right-handed collegiate tennis players. A 15-segment model was used to calculate the total body angular momentum about three orthogonal axes (X, parallel to the baseline; Y, normal to baseline and pointing towards the net; and Z, pointing upwards) passing through the centre of mass and to obtain the segmental contribution of the trunk, arms and legs. Most of the clockwise angular momentum about the X-axis was concentrated in the trunk and the racket-arm. Between the events of maximum external rotation and ball impact, the clockwise angular momentum about the X-axis of rotation of most body segments was reduced and the racket-arm gained clockwise angular momentum. The body angular momentum about the Y-axis of rotation had two distinct patterns and was the result of the lateral rotation of the trunk as the racket shoulder was elevated in preparation for impact. This body angular momentum was clockwise from the event of maximum external rotation to impact for the players with the greatest ball speed, whereas it was counterclockwise for the other players. The angular momentum about the Z-axis of rotation was small and lacked a consistent pattern. The largest source of angular momentum in the tennis serve derives from the remote angular momentum about the X- and Y-axes of rotation, which are then transferred from the trunk to the racket-arm and finally to the racket. Near impact, most of the angular momentum (75.1%) was concentrated in the racket-arm. Of the angular momentum of the racket-arm, the largest percentages were concentrated in the racket (35.9%) and the forearm segment (25.7%). 相似文献
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Knudson D Noffal G Bauer J McGinnis P Bird M Chow J Bahamonde R Blackwell J Strohmeyer S Abendroth-Smith J 《Sports biomechanics / International Society of Biomechanics in Sports》2003,2(2):267-277
To help instructors in evaluating innovations in biomechanics instruction, a standardised test of the key concepts taught in the introductory biomechanics course was developed. The Biomechanics Concept Inventory (BCI) consists of 24 questions that test four prerequisite competencies and eight biomechanics competencies. Three hundred and sixty seven students from ten universities throughout the United States took the test at the beginning and the end of the introductory biomechanics course. Analysis of a sub-sample of the students showed that the BCI was reliable with typical errors in internal consistency and test-retest conditions of 1.4 and 2.0 questions, respectively. Mean pre-test scores (8.5 +/- 2.0) significantly (p < 0.0001) improved to 10.5 +/- 3.2 in the posttest (n = 305). Typical biomechanics students could correctly answer half of the prerequisite questions on the pre-test. Instruction resulted in a mean normalised gain (g) of 13.0% of maximum possible improvement that was consistent with research on traditional instruction in introductory physics courses. It was concluded that the BCI could be an effective tool to evaluate the overall effect of pedagogical strategies on student learning of key biomechanical concepts in the introductory biomechanics course. 相似文献
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Rafael E. Bahamonde 《Journal of sports sciences》2013,31(8):579-592
Three-dimensional cinematography and the direct linear transformation method were used to obtain the coordinates of the landmarks of five right-handed collegiate tennis players. A 15-segment model was used to calculate the total body angular momentum about three orthogonal axes (X, parallel to the baseline; Y, normal to baseline and pointing towards the net; and Z, pointing upwards) passing through the centre of mass and to obtain the segmental contribution of the trunk, arms and legs. Most of the clockwise angular momentum about the X-axis was concentrated in the trunk and the racket-arm. Between the events of maximum external rotation and ball impact, the clockwise angular momentum about the X-axis of rotation of most body segments was reduced and the racket-arm gained clockwise angular momentum. The body angular momentum about the Y-axis of rotation had two distinct patterns and was the result of the lateral rotation of the trunk as the racket shoulder was elevated in preparation for impact. This body angular momentum was clockwise from the event of maximum external rotation to impact for the players with the greatest ball speed, whereas it was counterclockwise for the other players. The angular momentum about the Z-axis of rotation was small and lacked a consistent pattern. The largest source of angular momentum in the tennis serve derives from the remote angular momentum about the X- and Y-axes of rotation, which are then transferred from the trunk to the racket-arm and finally to the racket. Near impact, most of the angular momentum (75.1%) was concentrated in the racket-arm. Of the angular momentum of the racket-arm, the largest percentages were concentrated in the racket (35.9%) and the forearm segment (25.7%). 相似文献
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