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Kinematic characteristics of the bobsleigh team start

Victory in bobsleigh is considered highly influenced even pre-determined by engineering and technology. However, following the introduction of stringent technical rules that restricted the use of technological developments, such as structural damping and electronic control, the sport has become strongly dependent on the driver’s skills and crew start time. The sport uses the so called flying start; time is taken after crossing a line that is away from the actual starting point. The start procedure is strictly regulated and is described below. The crew pushes the sled from a wooden start block that must be at least 150 cm long, 20 cm wide and 5 cm high from the surface of the ice. The crew cannot pass the block or remove it prior to the start. Once the start is initiated the crew pushes the sled along the “push-off stretch” which is the part of the track between the start block (wooden board) and the first photoelectric cell. This stretch of the track is postulated to be 15 meters long with a gradient of 2%. As stipulated by the sport governing body FIBT (2014), after the first photoelectric cell (which represents the virtual start-line for the time-taking), the track must follow a straight path so that bobsleds starting off may reach a speed of 35 km/hr or 9.72 m/s. As a result the most important feature is to achieve maximum initial velocity of the sled rather than minimize the time from the start. This work considers the parameters that affect the start time and the initial velocity gained by the sled. The following four start phases were identified: Joint non-timed push-off, i.e. between the -15 to 0 m Driver loading Brakeman push phase Brakeman loading. To date specialists used timing gates and cameras to analyze the start. They provide valuable but insufficient information. We used accelerometers and force transducers to assess individual efforts and suggest optimal timing in the key points of the start. Based on the acceleration measurement the timing of the driver and brakeman loading (number of strides) were identified as the most important features in gaining and maintaining the maximum velocity. We have found that the necessary measurements to allow accurate a kinematic analysis are relative forces imparted by individual crew members (crucial for team selection), and sled’s velocity and acceleration. It is shown that the fastest sprinters are not necessarily the best team contributors as running synergy is crucial for optimal velocity profile generation. We also illustrate that once the crew is selected just acceleration could be used to optimize the start routine. In particular we illustrate how just the change of run-up length by the driver could deliver 2.5% increase of the initial velocity which could result in more than 5% reduction in the total time. It is shown that athletes need to reach running speed of more than 10 m in order to achieve the desirable speed of 9.8 m/s. The relatively simple system is highly effective in immediate and quantifiable feedback and practical ways to improve performance are discussed.
© Copyright 2016 21th Annual Congress of the European College of Sport Science (ECSS), Vienna, 6. -9. July 2016. Published by University of Vienna. All rights reserved.

Subjects: bobsledding start movement biomechanics acceleration sprint velocity sports equipment
Notations: technical sports
Published in: 21th Annual Congress of the European College of Sport Science (ECSS), Vienna, 6. -9. July 2016
Editors: A. Baca, B. Wessner, R. Diketmüller, H. Tschan, M. Hofmann, P. Kornfeind, E. Tsolakidis
Published: Wien University of Vienna 2016
Pages: 498-499
Document types: congress proceedings
Language: English
Level: advanced