Differences in dynamic alignment and flexibility between junior high-school and high-school female basketball players / 体力科学

To identify athletes at a higher risk of anterior cruciate ligament (ACL) injury, we developed a video-based screening test focused on hip abductor and rearfoot function. However, age differences in hip or reafoot motion as a contributor to dynamic knee valgus remains unclear. The purpose of this study was to determine how age differences contribute to hip or reafoot motions. Eighty-three female basketball players (41 junior high-school and 42 high-school students) agreed to participate in this study. Participants were measured for hip rotation angle, tibial rotation angle, ankle dorsi-flexion angle, navicular drop and general joint laxity. Subjects also performed single-legged squatting and drop landing from a 30 cm box. Knee-in distance (KID) and Hip-out distance (HOD) were measured using 2-dimensional video images filmed at 30 Hz. Additionally, Dynamic Trendelenburg Test (DTT) and Heel-Floor Test (HFT) were performed. The prevalence of HFT-positive in junior high-school and high-school athletes were not statistically different. DTT-positive during landing was more prevalent in junior high-school athletes than in high-school athletes (P<0.05). Junior high-school athletes demonstrated greater HOD values in squatting than high-school athletes (P<0.05). The range of motion in high-school athletes was significantly greater than in junior high-school athletes in tibial external rotation, hip internal and external rotation (p<0.01). The navicular drop in junior high-school athletes was significantly greater than in high-school athletes (p<0.01), however the navicular height was greater in high-school athletes (p<0.01). Player's age is an important consideration in ACL injury preventative conditioning.

Influence of bending the trunk forward during drop landing on muscles around the knee joint / 体力科学

The aim of the present study was to investigate whether personal hamstring muscular activation increased by landing with the trunk bent forward. First, 14 healthy female university students were instructed to perform normal drop landing from a 40 cm-high box on both legs. Second, subjects were directed to perform drop landing with the trunk bent forward. Using images obtained from a high-speed video camera, the upper center of mass was calculated in the sagittal plane for determining the differences in these landings. For 0.1 second after toe contact, the muscular activation of quadriceps femoris and hamstring muscles was analyzed using an electromyogram (EMG), and these findings were compared between the 2 types of landings. There was no significant difference in the activation of quadriceps femoris, but the activation tended to decrease during landing with the trunk bent forward. However, the activation of hamstring muscles increased significantly during landing with the trunk bent forward compared with that during normal landing. During landing with the trunk bent forward, the activation of hamstring muscles increased, and the activation of quadriceps femoris tended to decrease. Because contraction of hamstring muscles decreases tension in the anterior cruciate ligament, the findings of this study may help in the prevention of anterior cruciate ligament (ACL) injury.