Comparative Analysis of Three-Link Model in Deep Squatting / 医用生物力学

Objective To discuss rationality of the three-link model used in analysis on interactive dynamics of deep squatting, and clarify the source of differences in calculation of joint torque by three-link model and Visual 3D. Methods Eight subjects were selected to obtain kinematic data of the squat motion through Vicon. The second Lagrangian equation was used to establish the three-link dynamic equation. The joint torque was calculated based on the Mathematica programming. The results were compared with the calculation results of lower limb chain segment model by Visual 3D, and the similarity between the two results was evaluated by the coefficient of complex correlation (CMC). Results The CMC of hip joint and knee joint from 8 subjects was larger than 0.85, and the CMC of ankle joint was between 0.50-0.85. The joint torque calculated by three-link dynamic equation and Visual 3D was highly similar in hip joint and knee joint, and there was only a moderate similarity in ankle joint. Conclusions The three-link model can be used in further analysis on interactive dynamics of deep squatting, but the influence of interactive moment caused by ground reaction force (external moment) on ankle torque should be considered.

Time-series relationship to achieve performance on rebound drop jump / 体力科学

<p>The aim of this study was to demonstrate a time-series relationship in drop jump (DJ) from a pre-set state with improved performance. Twelve male college athletes performed a DJ from a height of 0.60 m. DJ performance was assessed with a DJ-index (jump height/contact time). Short-interval intracortical inhibition (SICI) was assessed as intracortical inhibitory circuit excitability in a pre-set state, calculated by using paired-pulse transcranial magnetic stimulation for the medial gastrocnemius muscle (MG). The H-reflex of the left MG and the ankle joint torque were calculated in the early phase of take-off. A significant correlation was shown between ⊿SICI during the pre-set state and the DJ index. Thus, we examined the relationships between phases, focusing on time-series relationships throughout the jump period. The results showed a significant correlation between ⊿SICI during the pre-set state and %H-reflex during the early phase of take-off, and peak ankle joint torque during take-off was also significantly correlated with %H-reflex during the early phase of take-off. A significant correlation was also demonstrated between ankle joint torque during take-off and the DJ-index. In conclusion, we observed a time-series relationship between DJ from a pre-set state and improved performance. A decrease of intracortical inhibitory circuit excitability in the pre-set state affects stretch-reflex facilitation during the early phase of take-off; stretch-reflex facilitation results in the development of a large force in the ankle joint during take-off, and this force develops ankle joint torque. These findings may be used to improve jump performance.</p>

Influences of body composition, force-generating capacity and jump performance on 50-m sprint velocity in circumpubertal boys / 体力科学

This study aimed to elucidate how body composition, force-generating capacity and jump performances are associated with 50-m sprint velocity in circumpubertal boys, in relation to sprint phases and maturation. One hundred thirty four circumpubertal boys were allocated to preadolescent or adolescent group on basis of the height at the peak height velocity of Japanese boys (154 cm) reported in literature: those with body heights over 154 cm as adolescent group and others as preadolescent group. Body composition was determined by bioelectrical impedance analysis. In addition to maximal voluntary isometric knee extension torque, the performances of counter movement jump (CMJ), rebound jump (RJ), standing long jump (SLJ) and standing 5-step jump (SFJ) were also measured. RJ-index was calculated by dividing height by contact time. The time of 50-m sprint was determined at 10-m intervals. Multiple regression analysis showed that in preadolescent boys, SFJ become a predictor for the sprint speed during acceleration phases, and SFJ, RJ-index and CMJ as predictors for the sprint speeds during maximal speed and deceleration phases. In the adolescent boys, age, CMJ, SLJ, and SFJ become a predictor for the sprint speed during acceleration phases, and torque relative to body mass, CMJ and SFJ were selected as predictors for the sprint speeds during maximal speed and deceleration phases. Thus, the current results indicate that force-generating capacity and jumping ability are determinants for sprint performance in circumpubertal boys, but the relative contribution of each of the two factors differs between preadolescent and adolescent stages and among the sprint phases.

THE CHANGES ON MECHANICAL WORK OF THE LOWER LIMB JOINTS DURING BASEBALL PITCHING IN A SIMULATED GAME / 体力科学

The purpose of this study was to investigate the changes on mechanical work of the lower limb joints during baseball pitching in a simulated game. One male college baseball pitcher threw 15 pitches in an inning for 9 innings (135 pitches) in an indoor pitcher's mound with two force platforms. Rest time between innings was 6 minutes. Three-dimensional positions of 47 reflective markers attached to subject were tracked by an optical motion capture system (Vicon Motion System 612, Vicon Motion Systems) with eight cameras (250Hz). For subject 75 fastball pitches (1st, 3rd, 5th, 7th, and 9th innings) were chosen for analysis.As the main results, the hip joint extension absolute and negative work of the stride leg decreased with increasing the number of pitches. The ankle joint extension absolute and negative work of the stride leg increased with increasing the number of pitches. These results suggest that the hip joint extension torque of the stride leg was needed to maintain for higher performance in baseball pitching.

RELATIONSHIP AMONG MUSCLE STRENGTH OF LOWER LIMBS, KINEMATICS AND KINETICS DURING TAKE OFF IN THE LONG JUMP-FOCUS ON THE KNEE JOINT AND THE HIP JOINT- / 体力科学

The purpose of this study was to investigate the relationship among torque, motion of lower limbs during the take-off phase and muscle strength of lower limbs. Subjects were 12 male track and field athletes who had a top record of 6.84±0.41 m. Several variables of the 12 subjects, such as displacement, velocity, angle and angular velocity, and maximum torque of the knee and hip joints during the take-off phase, were obtained from film analysis and measurement of lower limb strength by Biodex.<BR>The main results were as follows:<BR>1. Subjects who had a lower angular velocity of the take-off knee joint after landing showed a lower decreasing ratio of velocity during the takeoff phase.<BR>2. There was a significant relationship between records for the long jump and hip flexion torque of the take-off leg during the last part of the take-off phase (r=-0.678, P<0.05) .<BR>3. Subjects who showed a higher value of hip flexion torque of their free leg during the last part of the take-off phase showed lower take-off angles.<BR>4. There was a significant relationship between knee extension strengths (60, 180, 300 deg/s) and knee joint angles at the middle of the take-off phase (r=0.700 P<0.01, r=0.672 P<0.05, r=0.751 P<0.01) .<BR>5. Subjects who maintained a larger knee angle for their take-off leg indicated a decrease in knee extension torque of their take-off leg during the last part of the take-off phase.<BR>6. Subjects who showed higher hip extension strength made the transition to hip flexion torque of the take-off leg from the middle to the last part of the take-off phase.<BR>From these results, it can be seen that knee extension strength is important for efficient take-off, and hip joint torque is one of the factors that influences one's record in the long jump.

RELATIONSHIP BETWEEN THE ABILITY TO MAINTAIN JOINT TORQUE AND MUSCULAR ENDURANCE OF LOWER LIMBS DURING 400m RUNNING / 体力科学

A study was conducted to investigate the relationships among changes of joint torque of the lower limbs, sprint ability such as sprint speed, stride length and stride frequency in 400 m running, and muscular endurance of the lower limbs. Subjects were 11 male track and field athletes who had a 400m running time of 48.75±1.32s. The experiment was composed of videotaping sprint form at 160 m and 360 m points during 400 m running, and measuring muscular endurance of hip and knee flexion and extension using Cybex NormTM.<BR>The main results were as follows:<BR>1) There was a significant relationship between 400 m running time and ability to maintain a higher running speed at the 360 m point.<BR>2) Running speed, stride length and stride frequency decreased significantly at the 360 m point.<BR>3) Subjects who showed a smaller decrease in stride frequency at the 360 m could maintain higher running speed.<BR>4) Subjects who showed smaller decrease in maximal joint torque of the lower limbs at the 360 m could maintain a higher running speed.<BR>5) There was a significant relationship between an increase in support time and decrease in maximal joint torque of hip extension for the recovery leg.<BR>6) Ability to maintain joint torque during 400 m running was influenced by muscular endurance of the lower limbs.<BR>These results suggest that the ability to maintain torque needed for higher performance in 400 m running is influenced by muscular endurance of the lower limbs.

A Comparison between cyclists and noncyclists of joint torque of the lower extremities during pedaling / 体力科学

The purpose of this study was to compare the effect between cyclists and noncyclists of pedal rates on ankle, knee, and hip joint torque during pedaling exercises. Six male cyclists (CY) and seven male noncyclists (NC) pedaled at 40, 60, 90 and 120 rpm with a power output of 200 W. The lower limb was modeled as three rigid segment links constrained to plane motion. Based on the Newton-Euler method, the equation for each segment was constructed and solved on a computer using pedal force, pedal, crank, and lower limb position data to calculate torque at the ankle, knee, and hip joints. The average planter flexor torque decreased with increasing pedal rates in both groups. The average knee extensor torque for CY decreased up to 90 rpm, and then leveled off at 120 rpm. These results were similar to NC. The average knee flexor torque in both groups remained steady over all pedal rates. The average hip extensor torque for CY decreased significantly up to 90 rpm where it showed the lowest value, but increased at 120 rpm. For NC, the average hip extensor torque did not decrease at 90 rpm compared with 60 rpm, and was significantly higher than CY at 120 rpm (CY : 28.1 ± 9.0 Nm, NC : 38.6 ± 6.7 Nm, p<0.05) . The average hip flexsor torque for NC at 120 rpm increased significanly from 90 rpm, and was significantly higher than CY (CY : 11.6±2.9 Nm, NC : 22.6±11.8 Nm, p<0.05) . These results suggest that it would be better for cyclists to select a pedal rate of between 90 to 110 rpm to minimize joint torque, and, as a result, reduce peripheral muscle fatigue.