EVALUATION OF SOCCER BALL PROPERTIES AND THEIR EFFECT ON THE BRAIN

Praveen Kumar Sharma

doi:10.7273/000007088

Soccer is the most popular sport in the world, with an estimated 250 million active players worldwide and 3.5 billion spectators. The fundamental equipment needed for the game is the soccer ball. Due to its wide popularity soccer is played by all age groups, including men and women. Soccer is a contact sport where collisions can occur directly between players, head to ground contact, head to goal post contact, ball to head contact, etc. Soccer is a unique sport because it allows players to deliberately and purposely direct the ball with their heads—a technique known as "heading”. Since heading is a component of the game, this study examines the brain response to different head impacts using biofidelic models. The effect of different mechanical properties soccer ball during heading on brain response is investigated and identify the ways to reduce the brain injury due to heading. Soccer balls have been tested in laboratory conditions against rigid surfaces but have not been correlated to play conditions with recoiling impact surfaces. The experimental study compared the laboratory speed to play conditions and evaluated the impact of ball pressure on kicked ball speed. The average kicked ball speed increased from increased the ball pressure within the manufacturers recommended limits. For a shot on goal from 11 meters, this led to 13.5 mm less goalkeeper movement. Assessment of the risk of brain injury from ball heading in soccer was performed by numerical simulations of the ball head impact using a biofidelic Total Human Model for Safety (THUMS) model. A comparison was made between the effect on brain response to different impact locations, ball pressure, ball speed, and ball friction. Oblique impacts were the most severe, compared to normal and side impacts, producing 74% more maximum principal strain than normal impacts in the cerebellum region. The impact from a high ball speed at low ball pressure posed a greater risk of brain injury than a low-speed ball with high ball pressure. A 14% increase in ball speed increased the maximum principal strain by 25% and for a 25% increase in ball pressure, the maximum principal strain is increased by 7% in brain stem. For oblique impacts, the coefficient of friction was important. When friction increased from its lowest to its highest level, the brain experienced 130% more strain. The effect of the player size on brain response was investigated by comparing the brain response of three different sizes of biofidelic models. The result showed that a 95th percentile model experienced 36% less strain than the 5th percentile model. Balls weighing 435 gm and 290 gm were projected towards a 50th percentile model with the same energy. With the lighter ball (290 gm), more strain in the brain (up to 30%) was observed. Due to the popularity of soccer, it is played by both genders and children. The brain response of the male and female players was compared in this study. Total Human Model for Safety (THUMS) male 50th percentile whiplash model and female 50th percentile whiplash model were used to compare the brain response of teams of mixed gender. For the same ball pressure and speed, the linear and rotational acceleration of the 50th percentile female model increased by 44% and 16%, respectively, compared to the 50th percentile male model. For 35% less ball pressure and the same ball velocity, the 50th percentile female model shown 23% more linear acceleration and 2% less linear rotational acceleration than the 50th percentile male model. THUMS 5th percentile female model which is equivalent to 50th percentile 12-year youth is used to simulate the ball head impact with different ball sizes (size 4 and size 5). For the same energy of the balls before impact the size 4 ball impact produced 32% more linear acceleration and 26% more rotational acceleration.

EVALUATION OF SOCCER BALL PROPERTIES AND THEIR EFFECT ON THE BRAIN

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