Goalball, a Paralympic sport since 1976 in Toronto, is designed for visually impaired athletes. The goal is that two opposing teams, each consisting of three players try to score goals by rolling the
ball into the oppositions’ net. The court dimensions are the same as a standard volleyball court besides the lines of the court are tactile and are made by placing thick tape over cords. Players wear
blindfolds to guarantee equal impairments. The ball contains bells allowing players to echolocate movements. Alternating between offense and defence Goalball shows a very structured game play.
Offensively, the ball cannot be thrown until the referee calls “play”. The team has 10 seconds to throw the ball. If the player throws before the call or the ball doesn’t contact the landing area and
the neutral area, a penalty is incurred. Defensively, players listen for the ball and try to block it with their bodies. If unsuccessful, the opposing team wins a point. Once the players gain
possession, it’s their turn on offense.
The purpose of this study was to light up the relationship between ball speed and performance in Goalball. Therefore we developed an optical tracking system (GoalTrack) which uses computer vision
methods like background subtraction and shape recognition in order to detect the ball in video frames. Following a localization of ground contact points of the ball (minimum of pixel coordinates) plus
a projection of ball position to ground level at these times. According to Cohen, interrater-reliability between manual and automatically notation of sectors is high (kappa = .807)A result of this, is
the regression line of the ball through floor contact points. Bland and Altman analysis demonstrate a high level of agreement between this GoalTrack and manual annotation. For the 95% confidence
intervals a lower and higher limit of 1.3 m/s were detected.
Our results from performance analysis based on a sample of 8397 shots of the last paralympic tournament, Statistical analysis shows a correlation between scoring rate and ball speed, where speed seems
to be more important in womens goalball (Men: r = .65; Women: r = .90). The average speed of the ball did not decreased during the match. This leads to the conclusion that a training of explosiv
strength abilities should be prefered compared to endurance training