Impact Analysis of Bubble Soccer to Prevent Head Injuries
Authors: Rafi Mahir D. , Sadegh Ali M. , Frankel Zelda 
Published: January 2020

Abstract
Bubble soccer is a recreational soccer game that has gained huge popularity in recent years. In this modified soccer game, the players are strapped inside the hollow region of a “donut” shaped inflatable membrane, in a fashion similar to how a backpack is worn. Due to the large sizes of bubble membrane, collision among players is a major component of bubble soccer games, which often results in the players falling over and hitting the ground at high impact speed. To ensure that the player’s head doesn’t come in contact with the ground, Bubble ball Business Association (BBA) [3] recommends a minimum clearance of 20.3 cm between the player’s head and the top surface of the bubble membrane. This criteria, however, depends on the structural rigidity of the bubble ball, which is a function of its inflation pressure. This paper presents the results from a series of Finite Element studies, which sought to investigate the dynamic behavior of both bubble ball and soccer players in the aftermath of a vertical impact (with the player’s head and bubble ball both being upside-down), at gauge inflation pressures ranging from 3.45 kPa to 17.25 kPa, with the BBA specified head clearance. Even though vertical impacts of such nature are extremely unlikely in bubble soccer, it was preferred over oblique ground impacts as vertical impacts is capable of causing more sever impacts. Additionally, the results from the vertical studies can also serve as recommendations for side impacts with vertical walls and for head-on collisions among players. In all simulations, a medium sized bubble ball was considered with a player mass of 100 kg (25% more than BBA specification). The results showed that the player’s head, at a minimum inflation pressure of 10.35 kPa, would preserve 88% of the initial 20.3 cm clearance value, in the aftermath of impact. At pressures lower than this minimum value, it was observed that the ball didn’t inflate enough, and thus, wasn’t structurally rigid, to exert sufficient lateral force on the player’s body. As a consequence, the frictional force at the player-ball interface in the direction opposite to the impact was also low, which resulted in the player’s head hitting the ground. Since 10.35 kPa is a relatively high inflation pressure, it can cause significant damage of the internal organs of the player during impact, as well as can cause discomfort during the game. This may trigger the players to reduce the inflation pressure, which as these studies show, has dangerous consequences. Thus, further studies were conducted by increasing the initial clearance of the head to the ball’s top surface from 20.3 cm to 25.4 cm and 30.5 cm, which showed that the ball would prevent the head from hitting the ground at inflation pressures of 6.9 kPa and 1.725 kPa respectively. Thus, if the position of the strap within the ball is adjusted allowing for higher head clearance, lower inflation pressures are sufficient to prevent head injuries, which will improve the overall safety associated with bubble soccer. To improve current studies, more sophisticated human body models must be integrated in the simulations, which will allow the analysis of damages to the internal organs. Additionally, physical experiment must be conducted to validate current computational results.