Reliability of Three-Dimensional Angular Kinematics and Kinetics of Swimming Derived from Digitized Video

The purpose of this study was to explore the reliability of estimating three-dimensional (3D) angular kinematics and kinetics of a swimmer derived from digitized video. Two high-level front crawl swimmers and one high level backstroke swimmer were recorded by four underwater and two above water video cameras. One of the front crawl swimmers was digitized at 50 fields per second with a window for smoothing by a 4(th) order Butterworth digital filter extending 10 fields beyond the start and finish of the stroke cycle (FC1), while the other front crawl (FC2) and backstroke (BS) swimmer were digitized at 25 frames per second with the window extending five frames beyond the start and finish of the stroke cycle. Each camera view of one stroke cycle was digitized five times yielding five independent 3D data sets from which whole body centre of mass (CM) yaw, pitch, roll, and torques were derived together with wrist and ankle moment arms with respect to an inertial reference system with origin at the CM. Coefficients of repeatability ranging from r = 0.93 to r = 0.99 indicated that both digitising sampling rates and extrapolation methods are sufficiently reliable to identify real differences in net torque production. This will enable the sources of rotations about the three axes to be explained in future research. Errors in angular kinematics and displacements of the wrist and ankles relative to range of motion were small for all but the ankles in the X (swimming) direction for FC2 who had a very vigorous kick. To avoid large errors when digitising the ankles of swimmers with vigorous kicks it is recommended that a marker on the shank could be used to calculate the ankle position based on the known displacements between knee, shank, and ankle markers

THE APPLICATION OF FOURIER ANALYSIS TO DEMONSTRATE THE IMPACT OF THE FLUTTER KICK ON LONGITUDINAL ROTATION IN FRONT CRAWL

The contribution of the flutter kick to front crawl performance from its influence on longitudinal body rotation has not been thoroughly investigated. Fourier analysis was used to examine the impact of the kick on segmental and whole body angular momentum about the body’s longitudinal axis in fourteen elite front crawl specialists swimming at sprint and 400m pace. The third harmonic frequency, representing the effects of the six-beat flutter kick, was greater at sprint than 400m pace in lower limb, upper limb, and whole body angular momentum. The presence of the third harmonic in upper limb and whole body angular momentum indicates that the flutter kick has an influence on longitudinal body rotation. The role of the flutter kick in front crawl performance may be linked to actions of the torso muscles to help control longitudinal body rotation

Magnitude of maximum shoulder and hip roll angles in back crawl at different swimming speeds.

The purpose of this study was to identify the characteristics of maximum shoulder and hip roll angles in back crawl at different swimming speeds. Ten male elite swimmers performed back crawl at four different swimming speeds. The swimming trials were filmed by a total of six digital video cameras and three-dimensional coordinates of swimmer's anatomical landmarks were calculated using the three-dimensional direct linear transform. The data were input to a MATLAB programme to calculate linear and angular kinematics. Among the four speed trials, maximum shoulder and hip roll angles were unchanged, and maximum shoulder roll angle was significantly larger than maximum hip roll angle in all trials. In conclusion, the swimming speed does not affect swimmer's shoulder and hip roll angles in back crawl swimming

MAGNITUDE OF MAXIMUM SHOULDER AND HIP ROLL ANGLES IN BACK CRAWL AT DIFFERENT SWIMMING SPEEDS

The purpose of this study was to identify the characteristics of maximum shoulder and hip roll angles in back crawl at different swimming speeds. Ten male elite swimmers performed back crawl at four different swimming speeds. The swimming trials were filmed by a total of six digital video cameras and three-dimensional coordinates of swimmer's anatomical landmarks were calculated using the three-dimensional direct linear transform. The data were input to a MATLAB programme to calculate linear and angular kinematics. Among the four speed trials, maximum shoulder and hip roll angles were unchanged, and maximum shoulder roll angle was significantly larger than maximum hip roll angle in all trials. In conclusion, the swimming speed does not affect swimmer's shoulder and hip roll angles in back crawl swimming

A METHOD OF QUANTIFYING TORSO SHAPE TO ASSESS ITS INFLUENCE ON RESISTIVE DRAG IN SWIMMING

Torso shape characteristics such as cross-sectional area, curvatures and indentations influence the pressure distribution of fluid flow around the torso. The purpose of this study was to introduce a new method of quantifying torso shape using photographic imaging. The contours of the torso in the frontal and sagittal planes were obtained by tracing photographs of the swimmers. Anterior, posterior and lateral flow lines were interpolated to samples spaced at 1mm vertically and used to determine continuous form gradients of four elite male swimmers. The maximum rate of change in cross-sectional area was estimated from chest-waist and waist-hip by modelling each vertical sample of the torso as an ellipse. The method provides implications for discussion with coaches and athletes and future research to determine the role of torso shape in talent identification and swimming performance

Relationships between glide efficiency and swimmers' size and shape characterisitics

Glide efficiency, the ability of a body to minimize deceleration over the glide, can change with variations in the body’s size and shape. The purpose of this study was to investigate the relationships between glide efficiency and the size and shape characteristics of swimmers. Eight male and eight female swimmers performed a series of horizontal glides at a depth of 70 cm below the surface. Glide efficiency parameters were calculated for velocities ranging from 1.4 to 1.6 m/s for female swimmers (and at the Reynolds number of 3.5 million) and from 1.6 to 1.8 m/s for male swimmers (and at the Reynolds number of 4.5 million). Several morphological indices were calculated to account for the shape characteristics, with the use of a photogrammetric method. Relationships between the variables of interest were explored with correlations, while repeated-measures ANOVA was used to assess within-group differences between different velocities for each gender group. Glide efficiency of swimmers increased when velocity decreased. Some morphological indices and postural angles showed a significant correlation with glide efficiency. The glide coefficient was significantly correlated to the chest to waist taper index for both gender groups. For the male group, the glide coefficient correlated significantly to the fineness ratio of upper body, the chest to hip cross-section. For the female group the glide coefficient had a significant correlation with the waist to hip taper index. The findings suggested that gliding efficiency was more dependent on shape characteristics and appropriate postural angles rather than being dependent on size characteristics.</jats:p