Response Time as a Consideration in Design Constraints for Baseballs and Baseball Bats.
Principal Investigator: Mark D. Grabiner, Ph.D.
Institution: Department of Biomedical Engineering, The Cleveland Clinic Foundation, Cleveland, OH
Title: Response Time as a Consideration in Design Constraints for Baseballs and Baseball Bats.
Abstract: Baseball-related injuries in children range from minor to catastrophic. Catastrophic injuries usually involve an impact from a bat or a ball to the head or chest. Although serious injuries are documented in a wide range of baseball player age-groups and skill levels, children are at the greatest risk of serious and catastrophic injuries. From 1973 to 1980 there were 40 baseball- and softball-related deaths in children between 5 and 14 years of age. From 1986 to 1990, there were 16 baseball- and softball-related deaths recorded. More than 90 percent of the injuries involved head and neck injuries, and chest impact. Some of these injuries reflect an interaction between the performance characteristics of baseballs and baseball bats and the performance capacity of baseball players.
A premise of the presently proposed project is that the “factor of risk”, may be used as a design criterion for modification of the performance characteristics of balls and bats. In this regard, a performance characteristic to be “optimized” is the maximum ball exit velocity allowed by the ball-bat impact. The maximum ball exit velocity determines the transit time of the ball to a given field location. The transit time is used as the numerator in the factor of risk. It is reasonable that the maximum exit velocity should not exceed that which allows at-risk players (e.g., pitchers and infielders) adequate time to safely respond to the ball, that is player response time. Response time is used as the denominator in the factor of risk. A factor of risk value greater than 1.0 reflects a condition in which the potential for injury is increased. Therefore, the response time of baseball players is a physiologically justified design constraint. For the purposes of the presently proposed project, response time is defined as the minimum time required by an athlete to accurately place the gloved hand between an oncoming ball and his/her body within a specific window of time.
Purpose: By experimentally determining the expected minimum response times of young athletes performing a simulated baseball fielding task, the proposed project will determine the maximum, safe ball exit velocity for this age group.
Research Hypothesis: Response time of young athletes performing a simulated baseball fielding task is sensitive to conditions of ball trajectory, ball speed, and parallel performance of attention splitting tasks. It is expected that the slowest response times will occur during the conditions in which the ball trajectory is about head high and the subjects are performing the attention splitting task. The gender-specific 95th percent confidence interval will provide a physiologically justified design consideration for this population of athletes.
Design: The proposed project will have two levels of ball trajectory, three levels of ball speed, and two levels of parallel performance of attention splitting tasks. Baseballs will be projected at athletes who will stand in a standardized position behind a safety net. We anticipate recruiting 100 athletes, 50 girls and 50 boys, from 8 to 16 years of age, who participate in competitive/recreational baseball programs. The primary dependent variable will be response time, measured as the elapsed time from ball projection to the time at which the gloved hand is accurately placed between the oncoming ball and the athlete’s body. The data collection will include force plate and motion capture data. The instant of ball projection will be quantified electronically and synchronized with the motion capture and force plate data. The statistical design of the study is a between group (gender) 2 by 3 by 2 repeated measures ANCOVA (trajectory by ball speed by attention). Age will be analyzed as a covariate