STATICS BASED APPROACH TO EVALUATE THE EFFECT OF LANDING POSTURES ON KNEE FRONTAL PLANE MOMENT IN SINGLE LEG LANDING.—IMPLICATIONS FOR DETERMINING THE RISK-ELEVATING MOVEMENT FOR ANTERIOR CRUCIATE LIGAMENT INJURY— / 体力科学

The purpose of this study was to increase knowledge about the landing posture that induces anterior cruciate ligament (ACL) injury. Analysis was done to determine the knee abduction moment during single limb landing using our previously proposed mathematical model. Our model has proven that the criterion of knee abduction occurring is when the acting line of the ground reaction force is directed laterally to the lower leg segment. Based on this, we predicted a medial shift of the knee joint and a lateral leaning of the trunk segment to induce the knee abduction moment. To verify the results of our model prediction, we conducted a motion analysis experiment with a single limb-landing task. Three male and four female subjects participated in the experiment. Subjects were instructed to fall from a 30 cm high box and land on a target which was assigned by PC-controlled laser pointers. Since the landing target was unexpectedly moved during landing, the subjects were perturbed and exhibited various landing postures. The results of the landing experiment showed that trunk leaning laterally towards the landing limb and medially shifted knee alignment induced the knee abduction moment. These results are consistent with the results predicted by our model. In conclusion, appropriate control of both lower limb alignment and trunk motion in the frontal plane in essential for reducing the risk of ACL injury.

UPPER EXTREMITY MUSCLE ACTIVITIES AND STRENGTHS IN OVERHEAD THROWER DURING ECCENTRIC MUSCLE ACTION / 体力科学

PURPOSE : To determine the patterns of electromyographic (EMG) responses and torques of upper extremity muscles in overhead throwers during maximal, eccentric muscle action for shoulder flexion (Flex_Ecc), abduction (Abd_Ecc) and diagonal activities (Dia_Ecc) with full glenohumeral internal rotation, at 60, 120, and 180°/s on the dynamometer.METHODS : Seven asymptomatic subjects (7 men, 4 women) who participate in overhead sports at least three days a week volunteered to participate in this study. Subjects were randomly performed with the test procedure which consisted of at least 5 grade maximal-effort repetitions on the three different testing conditions, at 60, 120, and 180°/s on the dynamometer, while we assessed muscle activation of the anterior deltoid (AD), middle deltoid (MD), posterior deltoid (PD), upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and biceps brachii (BB) muscles by surface electromyography. EMG data was expressed as a percentage of maximum voluntary isometric contraction (%MVIC) that was obtained from the highest root mean square (RMS, 50 ms) of each muscle and was normalized and averaged.RESULT : AD muscle elicited lower muscle activity during Dia_Ecc than Flex_Ecc and Abd_Ecc (P＜0.05) while the MD, PD, UT, MT, and LT muscles elicited overall greater muscle activities during Dia_Ecc. MD and MT muscle activities were significantly greater for the faster speed than for the slower speed as 60°/s during Abd_Ecc (P＜0.05). Peak torque generated greater muscle strength for Dia_Ecc than Flex_Ecc and Abd_Ecc, and it was significantly greater for the faster speed than slower speed during Dia_Ecc (P＜0.05).CONCLUSION : Posterior upper extremity muscle activities and peak torque values were found to be dependent on eccentric muscle action for diagonal shoulder activity at the faster speed. This study provided evidence that isokinetic eccentric muscle strength testing of the posterior upper extremity muscle was effective to develop of a proper program for overhead sports athletes require forceful stability during deceleration phase.

EMG ANALYSIS OF UPPER EXTREMITY MUSCLES DURING ISOKINETIC TESTING OF THE SHOULDER JOINT / 体力科学

<b>Purpose</b> : This study was to investigate the patterns of electromyography (EMG) amplitude responses during maximal, eccentric muscle action with shoulder adduction and diagonal movement, at 6 different positions on the dynamometer.<b>Methods</b> : The participants for this investigation were 9 males and 5 females. Testing consisted of each subject performing eccentric muscle exercise of the dominant shoulder muscle at a velocity of 60°/sec and 180°/sec. Muscle activity values was recorded individually from six different muscles and peak torque values were extracted for each test from torque curves once. EMG data were normalized to the highest root mean square (RMS), and were expressed as a % maximum voluntary isometric contraction (%MVIC).<b>Results</b> : The posterior parts of upper extremity muscle complex generate overall high muscle activity (> 40%MVIC) during all testing for eccentric muscle activity with diagonal shoulder movement. Posterior deltoid (PD), upper trapezius (UT), and middle trapezius (MT) muscles show differences between eccentric muscle action with shoulder adduction and eccentric muscle action with diagonal shoulder movement.<b>Conclusion</b> : The present results show that an improved understanding of muscle activity patterns during different movement may benefit many fields of athletic trainers, coaches, and athletes, in addition to assisting in injury prevention for throwers, and even rehabilitation after injury.