Analysis of Forefoot Bending Angle in Sprint Spikes According to Bobsleigh Start Lap Time for Development of Korean-Specific Bobsledding Shoes

France won the gold medal in bobsleigh at the 1998 Nagano Winter Olympics. The finish times of this 6 km race varied within 0.1 second: France, in first place, had a time of 53.63 seconds, followed by Germany with 53.70 seconds, Great Britain with 53.71 seconds, and the United States with 53.73 seconds. At the 2014 Winter Olympics in Sochi, rankings were determined by combining the finish times from four runs, all of which varied within 0.1 seconds: Russia placed first, with a time of 3:40.60, followed by Latvia with 3:40.69, and the United States with 3:40.99. These results indicate that bobsleigh is one of the fastest winter sports, in which wins are determined by shortening the time spent on narrow ice tracks and achieved through extreme speeds and competition (Dabnichki, 2015). A bobsleigh run lasts approximately 60 seconds, and the sleigh should run along the ice track at a mean speed of 135 km/h for competitive speed and decreased completion time (Denny, 2011). This is closely associated with the postures, weights, and steering techniques of the players, as well as aerodynamic variables of the sleigh. Efforts have been made to improve these factors and ultimately shorten the time (Chowdhury, Loganathan, Alam & Moria, 2015; Ubbens, Dwight, Sciacchitano & Timmer, 2016). Recent studies focused on improving bobsleigh times found that shortening the start by 0.01 seconds could shorten overall lap time by 0.03 seconds, suggesting importance of the start (Dabnichki & Avital, 2006; Park, Kim & Park, 2015, Sabbioni, Melzi, Cheli & Braghin, 2016). In bobsleigh, starting involves teams sprinting approximately 30 m while pushing the 390 kg sleigh on a slippery surface. A strong propulsive force should be produced between the players' shoes and the ice surface in the starting area to decrease lap time and improve performance. Improvements in sports times have been associated with technological advancements in equipment. Bobsleigh shoes, along with the sleigh, helmets, and gloves, distribute the power of players onto the ice surface. Selection of appropriate shoes could act as a variable in improving the players' performance and times. In consideration of the various mechanical variables of each sport, forefoot bending angle has been modified in the general selection and development of athletic shoes. Forefoot bending angle in shoes is associated with ground reaction force and advancing force acceleration in terminal stance and pre-swing KJSB Korean Journal of Sport Biomechanics 2016; 26(3): 315-321 http://dx.doi.org/10.5103/KJSB.2016.26.3.315 http://e-kjsb.org eISSN 2093-9752 ORIGINAL