PROFILES OF ACTIVITIES OF THIGH MUSCLES DURING SPRINT RUNNING IN TRACK AND FIELD ATHLETES EXPERIENCED HAMSTRINGS (MUSCLE) STRAIN INJURY － DIFFERENCE BETWEEN INJURED AND NON INJURED LEGS － / 体力科学

The present study aimed to investigate the profiles of activities of thigh muscles during 100 m sprint running in track and field athletes experienced hamstrings (muscle) strain injury, with specific emphasis on the difference between injured and non-inured legs. The subjects were 20 track and field athletes who were divided into muscle strain injury group (MS) and non muscle strain injury group (NMS). The electromyograms (EMGs) of five thigh muscles (the biceps femoris, semitendinosus, rectus femoris, vastus lateralis and vastus medialis) and knee joint angles were recorded during 100 m sprint running. For NMS, there were no significant differences between the right and left legs. For MS, the averaged EMG of every muscle,expressed as relative to that during maximum voluntary contraction (%mEMG_MVC), values of the biceps femoris and semitendinosus in the latter phases of takeoff and swing periods were significantly higher in the injured leg than in the non-injured leg. Also, the maximal flexed and extended angles of the knee joint during takeoff and swing period, respectively, for the injured leg were significantly greater than those for non-injured leg. Thus, the present results indicate that track and field athletes experienced hamstrings (muscle) strain injury show by higher EMG activities in the biceps femoiris and semitendinosus of the injured leg at the later phases of swing and takeoff periods during 100 m sprint running. This may be partially related to the running style with a greater extended position of knee joint angles at the corresponding phases.

Effect of Flexion Angle of Knee Joint on Co-contractions of Agonist and Antagonist Muscles / 中国康复理论与实践

@# Objective To test the effect of different flexion angles of knee joint on the myoelectric activity and torque of quadriceps femoris and hamstring muscle when these muscles contracting.MethodsElectromyographic activities and isometric torque measurements were performed on 10 healthy subjects at 30°, 60° and 90° of knee joint flexion.ResultsThe results indicated that the greatest maximal voluntary isometric contracture-torque of quadriceps femoris occurred during knee extension at 60° of knee flexion ( P<0.01). However, no significant relationship of maximal voluntary isometric contracture-electromyography and maximal voluntary isometric contracture-torque of quadriceps femoris were found in 10 subjects. But when knee joint was at 90° flexion, hamstring muscle had a greatest neuro-myoelectric activity.ConclusionThe exercise of maximal voluntary isometric contraction of quadriceps femoris and hamstrings muscles at certain knee joint angle can help to maintain the stability of knee joint.

Effects of landing motion on power during takeoff in rebound drop jump. With special reference to angle at the knee joint / 体力科学

This study clarified the most appropriate landing motion for enhancement of the rebound drop jump index (RDJ<SUB>index</SUB>), which can evaluate the ability to perform ballistic and stretch-shortening cycle (SSC) movements. The RDJindex was calculated using the formula RDJ<SUB>index</SUB>= (1/8⋅g⋅RDJt<SUB>a</SUB><SUP>2</SUP>) /RDJt<SUB>c</SUB> where RDJt<SUB>c</SUB> and RDJt<SUB>a</SUB> are the contact and air times during a rebound drop jump from a height of 0.3 m (RDJ), a typical SSC movement. The relationships between the RDJ<SUB>index</SUB> and the characteristics of the knee and ankle joint motions during RDJ were examined in nine male jumpers. The results were as follows:<BR>(1) The characteristics of leg motion during the descending phase were that the ratio (%K-ANG) of displacement in flexion of the knee during the descending phase to that during both descending and takeoff phases was 48.6% and this preliminary motion started 53.6 ms before touchdown. Furthermore, as %K-ANG increaced, the contact time decreased (r=-0.784, p<0.05), the air time increased (r=0.874, p<0.01) and consequently, the RDJ<SUB>index</SUB> increased (r=0.891, p<0.01) . These results suggested that quick knee flexion just before touchdown is an important factor in increasing the RDJ<SUB>index</SUB>.<BR>(2) A characteristic of the leg motion during the takeoff phase was that the end point of knee flexion appeared 13.3 ms earlier than that of ankle dorsiflexion. That time increased as %K-ANG increaced (r=0.830, p<0.01), but conversely, as %K-ANG decreased markedly, end point of ankle dorsiflexion appeared earlier than that of knee flexion. These results suggested that preliminary motion of the knee would result in appropriate timing of the knee and ankle motions for shock absorption during the takeoff phase of RDJ.<BR>(3) An other characteristic of the leg motion during the takeoff phase was that the ratio of displacement of the knee in extension to that in flexion was 310.2%. This ratio increased as %K-ANG increaced (r=0.903, p<0.001) . These results suggested that preliminary motion of the knee would cause to increase displacement in extension for kick motion and yet to decrease displacement in flexion for shock absorption.<BR>These findings led to the conclusion that quick and short range flexion at the knee just before touchdown was an effective landing motion for enhancing the ability to perform ballistic and SSC movements.

Effect of hip and knee joint angles in response to a step out movement / 体力科学

The purpose of the present study was to determine whetehr differences exist between nine experimental conditions mixing 10°, 40°and 70°of hip joint angles with knee joint angles, when thirteen subjects performed the same response task. In the experiment 1, each subject was asked to stand on the inside two of the four mat switches (500×700 mm) and keep the assigned joint angles during a second of preparatory period. After the period, each subject was asked to respond with a step out on either the right or the left outside mat switch as quickly as possible. Then the data was collected analyzing the whole body choice response time (RESPONSE TIME) defined as the interval time from the signal to respond with step out, the whole body choice reaction time (REACTION TIME) defined as the interval time from the signal to reaction with lifting the leg for responding to the step out, and the movement time (MOVEMENT TIME) defined as the interval time subtracting RESPONSE TIME from REACTION TIME. Moreover, in the experiment 2, the data was collected and analyzed from the onset time of various forces from the two force platforms on which each subject stood instead of the mat switch and EMG which was led from the right side of m. rectus femoris, m, biceps femoris, m. gastrocnemius, m. tibialis anterior and the left side of m. quardriceps femoris, during performance of the response task. The results were as follows:<BR>1. The subjects' posture with each 70°flexion of the hip and the knee joint revealed the shortest RESPONSE TIME, because of the shortened MOVEMNT TIME, compared with the other posture. Conversely, the posture with 70° flexion of the knee joint showed an expanded REACTION TIME.<BR>2. The knee joint angle was an important factor effecting both REACTION TIME and MOVEMENT TIME, rather than the hip joint angle for the task of the experiment, since flexion of the knee joint expanded the REACTION TIME, but shortened the MOVEMENT TIME.<BR>3. The result of the force platform measurements indicated that the posture with each 70°flexion of the hip and the knee joint was shorter than that with each 10°flexion of them at the onset time of the first reaction force after the reaction signal, and that the order of response for the task was beginning at the leg for responding, followed by the other leg for keeping stability.<BR>4. Conclusive evidence for a shortened RESPONSE TIME was found in the facilitation of the central nervous system, which revealed the preliminary muscle activity and the stabilizing of the posture.