DLT Method Research Articles

Comparison of Film and Video Techniques for Estimating Three-Dimensional Coordinates within a Large Field

This study compared the errors produced with 3-D video and film analysis techniques using the DLT method with fixed cameras when the images cover a wide field of view. The results indicated that with a large field of view (8 meters) the accuracy of video analysis is clearly inferior to that of film analysis. However, within the volume of the control object, both film and video analyses are still precise enough for most practical purposes. Errors were larger in landmarks outside the control object than in the points of the control object. The maximum errors in the calculated positions of external landmarks were particularly large in the video analysis. However, even these rather large errors for points markedly outside the control object may be acceptable. It will depend on the requirements of each particular investigation.

スピードスケートにおける加速理論の再検討

Many researchers have attempted to measure the change in velocity of the center of gravity (CG) for speed skaters in stroking. However, there have been some difficulties in measuring the velocity change in speed skating; they include the very long stride length (about 10m) and the three-dimensional behavior of the skater's CG. The purposes of this study were to investigate the push-off technique for top-level Japanese speed skaters and the change in velocity during the push-off phase using 3D cinematography, and then to examine acceleration theory during the push-off phase in speed skating. Skaters participating in the 500m race of the All Japan student championship (1989) were videotaped (60 fields/s) by 10 VTR cameras over 20m at the crossing zone of the back straightaway. Twenty-two male skaters were selected as subjects and classified into two groups on the basis of the performance of the competition. 3D coordinates of the segment endpoints were obtained on five sub-areas (each 4m in length) using a DLT method. Displacement and velocity of the CG and the angles of the hip, knee and ankle joint were calculated. The results obtained are summarized as follows: 1) Push-off movement for the top group skaters placed the CG further forward than that of the second group. 2) The vector derived from the push-off movement for the top group skaters was directed forward, and accelerated the CG of the skaters effectively. 3) Increase in the velocity in skating direction for all subjects seemed to contribute more than expected to the acceleration of the CG. It has been proposed that acceleration in speed skating occurs by push-off of the leg in a direction perpendicular to the gliding direction of the skate, since the force applied to the opposite direction of gliding cannot contribute to acceleration of the CG due to very small frictional force. However, this theory cannot thoroughly explain the findings obtained for the top skaters in this investigation. Therefore, the acceleration theory should be modified to reflect the fact that the CG of the skater during speed skating is accelerated not only by the push-off perpendicular to the gliding direction but also by an increase in velocity vector in a gliding direction.

Intrasubject Variability of Upper Extremity Angular Kinematics in the Tennis Forehand Drive

The intra subject variability of the angular kinematics of the wrist and elbow joints in the tennis forehand drive were studied. Two varsity tennis players were filmed as they performed flat forehand drives. The DLT method of 3-D reconstruction was used to measure the angular motion of the upper extremity for eight strokes to assess the intra subject variability of selected kinematic variables. Curves were synchronized to impact and averaged. Wrist and elbow angular position data were quite consistent, with curve coefficients of variation (CV) less than 5.9%. The consistent angular positions during the forward stroke did not result from highly consistent patterns of angular velocities or accelerations. For both the wrist and elbow joints, intra subject variability increased for the angular velocity (CV = 90.6%) and angular acceleration (CV = 129.5%) curves. Biomechanical studies comparing derivatives or kinetic variables across subjects may have to be interpreted with reference to intra subject variability.

空中における身体の腕-捻りに関する研究

Twisting from a somersault is one of the most used techniques in sports with airborne components such as diving, gymnastics, and so on. The purposes of this study were to investigate the effect of arm swing on the production of aerial twist during somersault and to identify factors affecting the production of the twist. By using a model composed of three rigid bodies, the mechanism of the production of twist from a somersault was confirmed theoretically. Then, quantitative calculation was done based on the model. In the calculation a performer was assumed to swing one arm downward from the symmetrical position with both arms above the head. To validate the model, twisting somersaults of two male skilled gymnasts were filmed and analyzed with 3-dimensional cinematography (DLT method) to compare with the model. The performances were forward twist-somersaults of 1/2, 1 and 3/2 revolutions from a vaulting horse. The factors affecting the generation of twist are discussed based on the results of computer simulation and film data. The results are summarized as follows: 1) An asymmetrical arm swing could generate a twist about the longitudinal axis of the body from a somersault. This arm swing tilted the principal axes of the body away from their original positions. The axis of the angular momentum that was initially established did not change in the airborne phase, but the momentum resolved into two perpendicular components, one about the body's principal longitudinal axis and the another about the body's frontal axis (principal axis). Thus, the somersaulting motion around the frontal axis will continue even though the frontal axis is now tilted from its original position, and in addition the body will begin to twist about its longitudinal axis. 2) The direction of the twist depended upon the initial directions of the somersault and/or arm swing. 3) Large angular velocity of the somersault before the change in the posture and large swing angle of the arm were effective for the generation of twisting. The smaller the moment of inertia about body's longitudinal axis, the larger the twisting that was produced.

Kinetic analysis of the serving arm during the performance of the tennis serve

s-International Society of Biomechanics XII Congress 1989 983 KINETIC ANALYSIS OF THE SERVING ARM DURING THE PERFORMANCE OF THE TENNIS SERVE R.E. Bahamonde Dept. of Physical Education, Human Performance Laboratories Ball State University, Muncie, IN 47306, USA In order to investigate the patterns of motion of the serving arm and the muscular activity responsible for the motion, the resultant joint torque and force were calculated at the shoulder and elbow joints. Six male, right-handed, intercollegiate tennis players were filmed using the DLT method of 30 cinematography while they performed several trials of a hard driven flat serve. 3D coordinate data of 21 body landmarks and five racket points were obtained up to the instant of impact. The 30 data was smoothed usinq quintic spline functions. The serving arm was modeled as a four-segment kinetic chain consisting of the upper arm, forearm, hand, and racket. The inverse dynamics approach was utilized to calculate the resultant joint torque and force at the respective joints. The results indicated that during the backswing phase, small torques and forces were used to position the serving arm at the end of the phase which was defined as the instant of maximal elbow flexion (MEF). During the forward swing, the acceleration phase was mainly produced by the internal rotation and horizontal adduction torques at the shoulder and by a rapid extension torque at the elbow. The pronation/supination torque was negligible, but a large varus torque was present throughout the acceleration phase up to the instant of impact. BIOMECHANICAL DETERMINANTS OF THE RHYTHMIC STRUCTURE IN SPRINTERS START ACCELERATION Vadim K. Balsevich The Scientific Research Department State Central Institute of Physical Culture, Moscow, 105123, USSR. The dynamic and cinematic pammetres of running strides in start acceleration were investigated with a purpose to identify the factors which determine the specificity of its rhythmic picture. The registration of the dynamic curves of ground contact reactions as well as the time intervals of each consecutive stride in 60-meter distances of running with maximal speed was made by means of tensographical apparatus. The space characteristics of movement were analysed with a help of speed cyclography (100 frames per second). The comparative analyses of biomechanical characteristics of start acceleration (males 10, females 10) of international (8) and national (12) level were made. The results confii that the quality differences characterize the rhythm of start accelerations of sprinters of different qualification. Two types of the rhythmic pattern in start acceleration were identified. THE DYNAMIC MODEL OF SKELETAL MUSCLE: II. DYNAMICS OF THE TENDON AND JOINT R. Baratta and M. Solomonow Bioengineering Laboratory, Dep. of Orthopaedic Surgery Louisiana State University Medical Center, New Orleans, LA 70112 The impact of viscoelastic tendon stiffness and the joints soft tissue properties on the transmission dynamics of muscle force was studied. The dynamic models of a muscle subjected to sinusoidal contractions in the frequency range of .4-6 Hz were constructed experimentally for the M. gastrocnemius tendon and without its tendon. acting through the ankle joint, through its The results demonstrate that a linear second order model describes the muscle-tendon unit. T-test analysis (P<.O5) failed to identify any significant difference in the model due to shortening of its tendon, pointing out that the tendon acts as a stiff force transmission unit in isometric contractions of low to moderated force levels. Significant differences were present when the muscle acted via the ankle joint, resulting in a third order model which included the joints connective tissues (ligaments, cartilage, inactive tendons, etc.) properties. that tendon length may not be significant The results suggest while the joints connective tissue decrease in low to moderate isometric contractions, 1.5 Hz. the muscle performance range from 2 Hz to

A method for obtaining the 3D kinematics of the pelvis and thorax during locomotion

The DLT method was implemented on a SELSPOT-HP1000 system to study the 3d kinematics of the pelvis/thorax during locomotion. An important feature of our DLT implementation is an interactive calibration procedure which is flexible, accurate and fast. Extensive testing was used to validate the system both dynamically and statically.