Injuries due to jumping or falling are common among the participants in sports, such as basketball or skiing. It has been reported that 20% of all sports related injuries are due to jumping in games. Injury secondary to falls results in approximately 18,000 deaths in the United States. Thus, the necessity to provide quantitative and qualitative analysis of impact behaviour of ankles and knees due to jumping is strongly urged. The response of fracture or injury due to jumping is also important in designing of safety equipment related to sports. A linear elastic fracture mechanics approach has been used for the analysis.A standing jump was made by five Indian Olympic field hockey players on a force plate under standardized conditions. They weighed on average 757N and average 182 cm in height. The average vertical ground reaction force for the study ranged 3.9 times the body weight. Number of cycles to cause the failure of bone due to the repetitive number of jumps were obtained by using the following equation: af da Nf= ------ (1) where, Nf is the number of cycles of loading, a is the crack length. ÆK is the cyclic range of stress intensity factor, and C and m are constants, where a is the crack length, Nf is the number of cycles of loading. K is the cyclic range of stress intensity factor, and C and m are constants. Using ai = 10.0 x 10-8 m, C=1.0 x 10-8, m=1.25, and ÆK= 1.12 (F/A), equation (1) is integrated numerically with an increment of 10 x 10-6 m to the final value of the crack length (af) 10 x 10-6 m. The results are then used to obtain the rate of change of crack length with respect to the number of cycles (da/dN). Typical behaviour of crack growth rate characteristics for a force of F=2897 N and m being 1.25, reveals that 11 jumps are sufficient to cause micro-fracture of bone. This study also indicates the number of jumps for micro-fracture of human bone decreases as the value of m increases. It shows that shoes, and other supports, can also reduce the injury or propagation of bone crack. The study further reveals that micro-fracture due to jumping is sensitive to number of jumps. This analysis may further help in understanding of fracture fixation of bone. Model is being extended to evaluate accidents in other areas where falls are involved, eg parachuting.
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