| The purpose of this study was (a) to estimate the tibio-femoral and patello-femoral contact forces during the takeoff and landing phases of eight different types of vertical jumps (squat, countermovement, hop approach and drop jumps each with and without the use of arms) using musculoskeletal modeling techniques and (b) to determine whether there are significant differences in knee joint loads between genders and among the eight types of jumps. Data were collected from eight males and eight females with no known musculoskeletal disorders. Two S-VHS camcorders and two force plates were used to obtain 3-D kinematics and kinetics of the knee joint. An electromyographic assisted optimization model was used to estimate the tibio-femoral and patello-femoral joint contact forces. The major findings of this study were that (a) the peak tibio-femoral compressive contact forces ranged from 2,271 to 3,672 N (3.0 to 5.0 body weight, BW) for the males and from 1,415 to 2,073 N (2.5 to 3.7 BW) for the females; (b) the peak patello-femoral compressive contact force observed for the males ranged from 3,383 to 6,406 N (4.4 to 8.4 BW), whereas the same force for the females ranged from 1,830 to 2,594 N (3.3 to 4.6 BW); (c) a greater knee flexion is associated with greater joint contact forces transmitted to the knee; and (d) among the different jump types, the smallest joint contact forces were observed in the squat jump with and without arm movement during the ascending phase, and the counter movement jump with and without arm movement during the descending and ascending phases. The timing and patterns of the joint contact forces were fairly consistent between genders across different jump types. The loads from takeoff and landing seldom fell within the range that is considered to be damaging to cartilages at the knee. The cause of injuries may be due to either asymmetrical landing or prolonged stress acting on the knee joint. Therefore, excessive repetitions of jumping and landing, and deep squat positions should be avoided if the knee is subjected to abnormally high level of load over an extended period of time. |
