Kinesiologa

Muscle activity response to external moment during single-leg drop landing in young basketball players: The importance of biceps femoris in reducing internal rotation of knee during landing
Clinical Kinesiology Laboratory, Kitasato University Graduate School of Medical Science, Japan, 2 Kitasato University School of Allied Health Sciences, Sagamihara, Japan, 3 Department of Orthopaedic Surgery,Kitasato East Hospital, Japan
Abstract Internal tibial rotation with the knee close to full extension combined with valgus collapse during drop landing generally results in non-contact anterior cruciate ligament (ACL) injury. The purpose of this study was to investigate the relationship between internal rotation of the knee and muscle activity from internal and external rotator muscles, andbetween the internal rotation of knee and externally applied loads on the knee during landing in collegiate basketball players. Our hypothesis was that the activity of biceps femoris muscle would be an important factor reducing internal knee rotation during landing. The subjects were 10 collegiate basketball students: 5 females and 5 males. The subjects performed a single-leg drop landing from a 25-cmheight. Femoral and tibial kinematics were measured using a 3D optoelectronic tracking system during the drop landings, and then the knee angular motions were determined. Ground reaction forces and muscle activation patterns (lateral hamstring and medial hamstring) were simultaneously measured and computed. Results indicated that lower peak internal tibial rotation angle at the time of landing wasassociated with greater lateral hamstring activity (r = -0.623, p < 0.001). When gender was considered, the statistically significant correlation remained only in females. There was no association between the peak internal tibial rotation angle and the knee internal rotation moment. Control of muscle activity in the lateral to medial hamstring would be an important factor in generating sufficientforce to inhibit excessive internal rotation during landing. Strengthening the biceps femoris might mitigate the higher incidence of non-contact ACL injury in female athletes. Key words: ACL injury, risk factors, knee moment, muscle activation.

Meguru Fujii 1, Haruhiko Sato 2
1

and Naonobu Takahira 1,2,3

Introduction
In many sports injuries, anterior cruciate ligament (ACL) injury isknown to be serious enough to require a relatively long time for athletes to return to sports activities. Despite improvements in anterior cruciate ligament reconstruction techniques, two-thirds of ACL patients do not return to the pre-injury level of competitive sports by 12 months (Ardern et al., 2011). Therefore, ACL injury prevention is an important issue for athletes. The main focus ofpreventing ACL injury has been avoiding non-contact injury. The rate of non-contact injury among ACL injuries is approximately 70% (Hewett et al., 2006). Moreover, contact injury of the ACL, which occurs as a result of player-to-player contact, usually

results from unanticipated situations and is unavoidable in contact sports. Thus, it is important for prevention to find out the reason why ACL injuryoccurs in non-contact situations. Gender differences in the incident rate have been a focus in exploring the mechanism of non-contact ACL injury. The injury rate is 3.3–4.9 times higher in female athletes than in male athletes in basketball and soccer (Agel et al., 2005). There have been numerous studies concerning the kinematic differences in the knee joint between males and females innon-contact situations (Chappell et al., 2007; Ford et al., 2003; Kernozek et al., 2005; Kiriyama et al., 2009; Nagano et al., 2007; Russell et al., 2006). Female athletes exhibit increased knee valgus and decreased knee flexion in cutting tasks (James et al., 2004; Malinzak et al., 2001), and increased knee valgus and increased knee internal rotation in landing tasks (Chappell et al., 2007; Ford et al.,...