Influence of the torque generating capacity of the lower extremity muscles on the running and jump performance in primary and junior high school boys / 体力科学

This study aimed to determine the relationships between the torque generating capacity of the lower extremity muscles and either running or jump performance in primary and junior high school boys. A total of 102 primary and junior high school boys participated in this study. Muscle thicknesses (MTs) of the knee extensors and plantar flexors were determined using ultrasonography. Muscle volumes (MVs) of the knee extensors and plantar flexors were estimated using MTs and limb lengths. The isometric joint torques (TQs) for knee extensors and ankle plantar flexors were measured using myometer. MV and TQ were divided by body mass (MV/BM and TQ/BM, respectively). Running velocity was measured using a non-motorized treadmill. The counter movement jump (CMJ) and squat jump (SJ) were performed on a matswitch system. The flight time was measured and used to calculate the heights of CMJ and SJ using the following equation; height (cm) = g × (flight time)² /8/10. As the result of multiple regression analysis, age, MV/BM and TQ/BM were selected as predictors of running velocity in the primary school boys, whereas TQ and lean body mass in junior high school boys. In the primary school boys, TQ/BM and body fat mass was selected as significant contributors for SJ and CMJ performances, whereas, in the junior high school boys, TQ and the percent of body fat for SJ performance and MV/BM and TQ for CMJ performance. Thus, the present results indicate that the relationships between torque generating capacity of the lower extremity muscles and either running or jump performance differ between primary and junior high school boys. It may be assumed that, for running and jump performances, muscle mass and strength become determinant factors in junior high school boys, whereas their values relative to body mass in primary school boys.

LONGITUDINAL HEIGHT VELOCITY DURING ADOLESCENCE AND ITS RELATIONSHIP TO SPORTS INJURY / 体力科学

Purpose: We compared longitudinal height velocity between subjects with Osgood Schlatter Disease (OSD) and those with other chronic lower leg diseases (LD) group involving the knee in order to examine the utility of this velocity as an indicator of bone axis development.Method: Subjects included 92 adult men who have played organized sports. Height values at 9 to 15 years of age were individually approximated by fitting 6-degree polynomial functions. Each polynomial function was differentiated to be led the height velocity curve. Timing of growth spurt and values of height velocity in the OSD and LD group were compared to those in a normal (N) group.Results: Peak height velocity (PHV) was accelerated in the OSD group compared to the LD group. When individual velocity curves were aligned by age of peak height velocity (PHA), the average height velocity in the OSD group was higher than that in the N group at 0.8 years after PHA. Furthermore, when the averaged velocity curve of each group was shifted based on the average PHA, the height velocity in the OSD group was significantly greater than that in the N group at ages 11.6–12.5 years. However the height velocity in the LD group was greater at ages 10.6–10.8 years and 13.3–14.0 years, smaller at ages 11.8–12.3 years than that in the N group.Conclusion: Subjects with OSD may possess higher height velocity than normal individuals before PHA. Conversely, subjects with LD seem to be related to other complicated factors.

VALIDATION OF A TWO-DIMENSIONAL MOTION ANALYSIS TECHNIQUE FOR QUANTIFYING DYNAMIC KNEE VALGUS DURING A DROP LANDING BY COMPARISONS TO DATA FROM THREE-DIMENSIONAL ANALYSIS / 体力科学

Dynamic knee valgus is considered a risk factor of non-contact anterior cruciate ligament (ACL) injury. To identify athletes at a higher risk, we developed a two-dimensional (2D) video-based screening test that determines hip abductor function as well as dynamic hindfoot and knee valgus. The purpose of this study was to validate the accuracy of the indices for dynamic knee valgus derived knee-in distance (KID) and hip-out distance (HOD) from the 2D-video.Twenty healthy university students agreed to participate in this study. Subjects were asked to step off a 30-cm box and land on one leg. This procedure was recorded simultaneously using a 2D video camera in the frontal plane and the Vicon motion capture system. Pearson's correlations examined associations between KID, KID normalized by height (KID/H), HOD, as well as HOD normalized by height (HOD/H) and 3D-valgus (knee valgus) or 3D-IR (tibial internal rotation).Significant correlations were found between the KID and 3D-valgus (r=0.72, p<0.01) and KID/H and 3D-valgus (r=0.73, p<0.01). Associations were not significant between KID and 3D-IR (r=0.08) and between KID/H and 3D-IR (r=0.03). A positive moderate correlation between HOD and 3D-valgus (r=0.46, p<0.05) and HOD/H and 3D-valgus (r=0.50, p<0.05), as well as a negative moderate correlations between HOD and 3D-IR (r=-0.52, p<0.05) and between HOD/H and 3D-IR (r=-0.51, p<0.05) were also observed.We conclude that KID is a reliable alternative for the 3D-valgus and the HOD is for the 3D-valgus and tibial external rotation.

STUDY ON THE EVALUATION OF KNEE JOINT PROPRIOCEPTION WITH A FOCUS ON HAMSTRING FUNCTION / 体力科学

This study was performed to establish a simple method to evaluate knee joint proprioception by examining knee-bending angle, in which Lombard's Paradox phenomenon could be confirmed, in 8 extremities of 7 patients with ACL injured who were diagnosed with ACL rupture at a medical facility (ACL injured group) and 10 extremities of 10 healthy adults (control group). As a result, knee joint proprioception in the ACL injured group was significantly lower than that in the control group (P<0.05). Significantly more incidence of Lombard's Paradox phenomenon was confirmed at the knee-extension position in the ACL injured group (P<0.01), compared with the control group. Significant negative correlation was confirmed between the reproductive angle inaccuracy of joint position sensation, a marker of knee joint proprioception, and Lombard's Paradox phenomenon under the conditions of r=-0.58 and the risk rate of 5%. Based on the results of this study, it was suggested that the knee-bending angle, in which Lombard's Paradox phenomenon was confirmed, would be affected by knee joint proprioception through feedback from the ACL mechanoreceptors, and the angle might be used as a simple evaluation method for knee joint proprioception.

ASSOCIATION BETWEEN HIP AND HINDFOOT DYNAMIC ALIGNMENT AND DYNAMIC KNEE VALGUS IN HIGH SCHOOL FEMALE BASKETBALL PLAYERS / 体力科学

Dynamic knee valgus is considered a risk factor of noncontact ACL injuries. The aim of this study was to determine the association between hip and hindfoot dynamic alignment and dynamic knee valgus.This cross-sectional study involved 88 high school female basketball players (175 legs). Subjects performed single-leg squatting and drop landing which provided a hip-out distance (HOD) and a knee-in distance (KID) via 2D video images. Hip and hindfoot dynamic alignment was evaluated by a dynamic Trendelenburg test (DTT) and a heel-floor test (HFT), respectively, during squatting and landing.The DTT-positive group (dynamic hip mal-alignment with lower non-weightbearing pelvis) demonstrated greater HOD and KID values for both squatting (p＜0.001) and landing (p＜0.001) than the DTT-negative group. The HFT-positive group (5^o or greater hindfoot valgus) demonstrated greater KID values for both squatting (p＜0.01) and landing (p＜0.001), but smaller HOD value for squatting (p＜0.01) than the HFT-negative group.In conclusion, dynamic hip mal-alignment may be associated with both greater HOD and KID, but hindfoot valgus only with greater KID.

CHANGES IN INTRA-ABDOMINAL PRESSURE AND TRUNK ACTIVATION DURING DROP JUMP / 体力科学

This study examined changes in intra-abdominal pressure and trunk activation during drop jump and the influence of those factors on performance. Intra-abdominal pressure (IAP) and surface electromyography (EMG) activity from the rectus abdominis (RA), transversus abdominis-internal oblique (TrA-IO) and erector spinae (ES) muscles were measured in seven males (22.3±1.0 years) during double-leg drop jumps from a 0.4 m height. Development of IAP (ΔIAP) and normalized rmsEMGs were calculated in the pre-contact, impact and push-off phases, after divided by ground reaction force data. TrA-IO activation which occurred prior to ground contact were the earliest and strongest compared to other muscles activation during each phase.ΔIAP during the impact phase coincided with the peak vertical force. There were significant positive correlations between ΔIAP, TrA-IO activation and vertical force per weight. In addition, the contact time correlated negatively with ΔIAP, TrA-IO activation and vertical force per weight. These findings indicate that ΔIAP and TrA-IO activation may contribute to trunk stability and efficient landing during double-leg drop jump.

Characteristics of torque production at the lower limb joints with special reference to type of muscle contraction / 体力科学

A study was conducted to investigate the relationship between the characteristics of torque production with special reference to eccentric and concentric muscle contraction and the structural and functional properties at the lower limb joints in the human kinetic chain. Ten male college athletes were tested with a isokinetic dynamometer (biodex) for eccentric and concentric torques during extension and flexion at the hip and knee, and plantar flexion and dorsiflexion at the ankle (angular velocity ; 30, 60, 120 deg/s) . The peak eccentric and concentric torques were higher in the order hip, knee and ankle joints, as the size of each muscle acting on its joint increased. However, the rate of peak concentric to eccentric torque (CON/ECC, %) was higher at the ankle joint than at the hip and knee joints. They tended to increase in the order of angular velocity ; 30, 60, 120 deg/s. These results suggest that the ankle joint is charactered by higher eccentric torque production. This characteristic is probably due to the fact that (1) the ankle joint is located at the end of the human kinetic chain and plays a role in transmitting the power to the ground effectively, (2) the muscle tendon complex acting at the ankle joint must have increased stiffness and tolerate great stretch loads to store and reuse the amount of elastic energy, (3) the hip and knee joints located at the center are the main sources of power supply. On the other hand, no significant correlations were observed among the torques at the hip, knee and ankle. These results suggest that torque production is independent at each of the lower limb joints, and is based on the structural and functional properties of each joint. These findings seem to be useful to clarifying the methods of strength and power training that can be adapted to the characteristics of torque production and the structural and functional properties of the hip, knee and ankle joints.

Lower extremity function for shock attenuation during landing on one leg / 体力科学

A study was conducted to investigate the cushioning effects of lower extremity functions on shock attenuation during landing on one leg.<BR>Optical methods were used to investigate the cushioning effects of lower extremity functions, since these facilitated the quantitation of kinematic variables such as angle, change in angle, position, displacement and velocity during the landing. The subjects were 5 healthy students ranging in age from 21 to 24 years. Ground reaction force (GRF) was measured with a force platform. The impact force peaks showed vertical force-time averages for 1 subject landing on one leg or two legs for 10 trials each from a height of 10cm.<BR>The peak/body weight of impact force of GRF upon landing was attenuated by the cushioning effects of the lower extremity functions, i. e. bending of the knee and ankle joints, more effectively on two legs than on one.<BR>Supination and pronation of the ankle joint influenced the impact force peaks, and the results of this experiment demonstrated significant difference between the number of discharge bursts of leg muscles upon landing on one leg and those landing on two, the former being higher.

AN ELECTROMYOGRAPHICAL ANALYSIS OF PURPOSIVE MUSCLE ACTIVITY AND APPEARANCE OF MUSCLE SILENT PERIOD IN ARCHERY SHOOTING / 体力科学

Shooting an arrow is a typical example of the physiological neck reflex. To get a good record in the archery competition, highly reproducible release is required during the drawing of a bow.<BR>In this study, first, the mechanics of shooting were analysed by means of EMG, progressive photographing and bow strain signals, employing two groups of college student archers (semi-skilled and unskilled) . These results were compared with those of the world top-class archers. And second, the rate of muscle silent period appearance, its latent time and release reaction time were measured from the three groups of college student archers (skilled, semi-skilled and unskilled) . The following results were obtained:<BR>1. Some distinct differences were recognized in muscle activities during shooting, such as “set up”, “draw”, “full draw”, “release” and “follow through” between the top-class archers and college archers (semi-skilled and unskilled) .<BR>2. In the case of two top-class archers, muscle silent period prior to release was observed in m. deltoideus (pars acrominalis) of both arms and m. trapezius (pars transversa) of the pushing arm.<BR>3. In the skilled college student archers, high rate of silent period appearance (70-100%) were observed and the values of its latent time and release reaction time falled in a very narrow range of 110-120 msec and 170-180 msec, respectively.<BR>4. Before the release, when m. deltoideus of the pulling arm was silent, ipsilateral m. trapezius began action. This muscle activity was cleary observed almost only in the case of skilled archers. Hence, this pattern of muscle activity may be accomplished by long time training.