PILOT STUDY: KINEMATIC ANALYSIS OF THE TECHNIQUE OF THE DEEP WATER START IN THE WATER SKIING

Abstract

The discipline "Water Skiing" is part of the curriculum of the mandatory discipline "Methodology of Water Sports Training" from the curriculum of the Bachelor's Degree Program "Physical Education and Sports" of the South-West University "Neofit Rilski", Blagoevgrad, Bulgaria. Also, this discipline is studied by all sports educators in Bulgaria, which is why we chose to analyze, from a biomechanical aspect, the element "deep water start". It is essential for quality water skiing training, because its mastery guarantees continuity in training and performing water skiing slalom in open water. This pilot study will provide a clear idea of the starting position of the body, the angular position of the water skis relative to the water surface. The forces acting on them will be analyzed and we will provide parameters for dynamic stability at startup. The aim of the present study is to perform a kinematic analysis of the deep water start technique. To establish the position and transposition of the kinematic segments of the chain when performing a deep water start in water skiing. There is not enough data in the world literature on this type of kinematic analysis. A small number of publications have been published in this area, mainly relating to kinetic analysis related to the strength characteristics of sports performance in water skiing (Silva, Ribeiro, Figueira, & Pinho, 2022). In this study, we will focus on the spatial and spatiotemporal structures of the start, as well as determine the influence of the overall Center of Gravity on the line of the water ski while maintaining the angle of attack when leaving the water. As well as the conditions for dynamic balance when starting from deep water and guiding the skis and the trajectory of the Center of Gravity in the phase structure of the exercise. For the kinematic analysis, we used photographic material that was filmed in the water area of Urdoviza Bay, the town of Kiten, as part of water skiing training. Anthropometric characteristics of the examined person: height 177 cm, weight 76 kg, age 28, BMI 24.3 кг/м2. We used a camera to record the cyclograms Go Pro HERO 12 Black HDR 5.3K, 4K. The graphic processing was done with a program PAINT 3D, Windows 10. The water skis used in this study were Jobe 170,18 cm long. For the kinematic analysis, we determined the projections of the transposition of the CG; the phases of starting from deep water; we analyzed the position of the body and limbs in the starting phase; the angular positions between the mechanical centers in the joints; conditions for dynamic stability.
We defined three main phases of the studied element, with the first phase divided into 3 subphases as follows: 1) first phase; 1a subphase of underwater starting position; 1b lifting subphase; 1c subphase of exiting the water; 2) second phase of stabilization of the stance; 3) phase of stable stance and guiding the skis on the water surface. We determined the location of the Center of Gravity in each of the phases and through projection we determined its trajectory of movement.
The kinematic analysis performed shows us that the location of the CG (even if it is outside the athlete's body) always lies on the imaginary line that connects the fulcrum of the feet with the partial center of gravity of the head from the kinematic chain. We determined the angles between two adjacent mechanical axes acting at a joint center. The skier's balance on the skis was considered as a lever system of the first kind (expressed by the formula P1 x r1 = P2 x r2), in dynamic equilibrium.