Sanders Ross H, Gonjo Tomohiro, McCabe Carla B
Faculty of Health Sciences, The University of Sydney , Sydney, Australia.
Institute of Sport Physical Education and Health Sciences, The University of Edinburgh , Jordanstown, UK.
J Sports Sci Med. 2015 May 8;14(2):441-51. eCollection 2015 Jun.
The purpose of this study was to explore the reliability of estimating three-dimensional (3D) linear kinematics and kinetics of a swimmer derived from digitized video and to assess the effect of framing rate and smoothing window size. A stroke cycle of two high-level front crawl swimmers and one high level backstroke swimmer was recorded by four underwater and two above water video cameras. One of the front crawl swimmers was recorded and digitized at 50 Hz with a window for smoothing by 4(th) order Butterworth digital filter extending 10 frames beyond the start and finish of the stroke cycle, while the other front crawl and backstroke swimmer were recorded and digitized at 25 Hz with the window extending five frames beyond the start and finish of the stroke cycle. Each camera view of the stroke cycle was digitized five times yielding five independent 3D data sets from which whole body centre of mass (CM) component velocities and accelerations were derived together with wrist and ankle linear velocities. Coefficients of reliability ranging from r = 0.942 to r = 0.999 indicated that both methods are sufficiently reliable to identify real differences in net force production during the pulls of the right and left hands. Reliability of digitizing was better for front crawl when digitizing at 50Hz with 10 frames extension than at 25 Hz with 5 frames extension (p < 0.01) and better for backstroke than front crawl (p < 0.01). However, despite the extension and reflection of data, errors were larger in the first 15% of the stroke cycle than the period between 15 and 85% of the stroke cycle for CM velocity and acceleration and for foot speed (p < 0.01). Key pointsAn inverse dynamics based on 3D position data digitized from multiple camera views above and below the water surface is sufficiently reliable to yield insights regarding force production in swimming additional to those of other approaches.The ability to link the force profiles to swimming actions and technique is enhanced by having additional data such as wrist and foot velocities that can be obtained readily from the digitized data.Sampling at 25 Hz with at least 5 samples before and after the period of interest is required for reliable data when using a 4th Order Butterworth Digital Filter.
本研究的目的是探讨从数字化视频中估算游泳者三维（3D）线性运动学和动力学的可靠性，并评估帧率和平滑窗口大小的影响。通过四个水下摄像机和两个水上摄像机记录了两名高水平自由泳运动员和一名高水平仰泳运动员的一个划水周期。其中一名自由泳运动员以50Hz的频率进行记录和数字化处理，使用四阶巴特沃斯数字滤波器进行平滑处理的窗口在划水周期的开始和结束后延伸10帧，而另一名自由泳和仰泳运动员则以25Hz的频率进行记录和数字化处理，窗口在划水周期的开始和结束后延伸5帧。划水周期的每个摄像机视图都进行了五次数字化处理，得到五个独立的3D数据集，从中得出全身质心（CM）分量速度和加速度以及手腕和脚踝的线性速度。可靠性系数范围从r = 0.942到r = 0.999，表明这两种方法都足够可靠，能够识别左右手划水过程中净力产生的实际差异。当以50Hz的频率进行数字化处理并延伸10帧时，自由泳数字化的可靠性比以25Hz的频率进行数字化处理并延伸5帧时更好（p < 0.01），仰泳的数字化可靠性比自由泳更好（p < 0.01）。然而，尽管对数据进行了延伸和反射，但在划水周期的前15%，CM速度、加速度和足部速度的误差比划水周期的15%至85%期间更大（p < 0.01）。要点基于从水面上下多个摄像机视图数字化的3D位置数据的逆动力学足够可靠，除了其他方法之外，还能提供有关游泳中力产生的见解。通过获取额外的数据，如可以从数字化数据中轻松获得的手腕和足部速度，将力分布与游泳动作和技术联系起来的能力得到了增强。当使用四阶巴特沃斯数字滤波器时，为了获得可靠的数据，需要以25Hz的频率进行采样，并且在感兴趣的时间段前后至少有5个样本。
