Journal of Sports Science and Medicine
Journal of Sports Science and Medicine
ISSN: 1303 - 2968   
Ios-APP Journal of Sports Science and Medicine
Androit-APP Journal of Sports Science and Medicine
©Journal of Sports Science and Medicine (2015) 14, 441 - 451

Research article
Reliability of Three-Dimensional Linear Kinematics and Kinetics of Swimming Derived from Digitized Video at 25 and 50 Hz with 10 and 5 Frame Extensions to the 4th Order Butterworth Smoothing Window
Ross H. Sanders1, , Tomohiro Gonjo2, Carla B. McCabe3
Author Information
1 Faculty of Health Sciences, The University of Sydney, Sydney, Australia
2 Institute of Sport Physical Education and Health Sciences, The University of Edinburgh, Jordanstown, UK
3 School of Sport, Ulster University, Jordanstown, UK

Ross H. Sanders
‚úČ Faculty of Health Sciences, The University of Sydney, Cumberland Campus C42, 75, East St, NSW, 2006, Australia
Publish Date
Received: 09-09-2014
Accepted: 23-03-2015
Published (online): 01-06-2015
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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 4th 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 words: Inverse dynamics, reliability, swimming, asymmetry, Butterworth filter

           Key Points
  • An 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.
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