Optimal coordination of maximal-effort horizontal and vertical jump motions – a computer simulation study

<p>Abstract</p> <p>Background</p> <p>The purpose of this study was to investigate the coordination strategy of maximal-effort horizontal jumping in comparison with vertical jumping, using the methodology of computer simulation.</p> <p>Methods</p> <p>A skeletal model that has nine rigid body segments and twenty degrees of freedom was developed. Thirty-two Hill-type lower limb muscles were attached to the model. The excitation-contraction dynamics of the contractile element, the tissues around the joints to limit the joint range of motion, as well as the foot-ground interaction were implemented. Simulations were initiated from an identical standing posture for both motions. Optimal pattern of the activation input signal was searched through numerical optimization. For the horizontal jumping, the goal was to maximize the horizontal distance traveled by the body's center of mass. For the vertical jumping, the goal was to maximize the height reached by the body's center of mass.</p> <p>Results</p> <p>As a result, it was found that the hip joint was utilized more vigorously in the horizontal jumping than in the vertical jumping. The muscles that have a function of joint flexion such as the m. iliopsoas, m. rectus femoris and m. tibialis anterior were activated to a greater level during the countermovement in the horizontal jumping with an effect of moving the body's center of mass in the forward direction. Muscular work was transferred to the mechanical energy of the body's center of mass more effectively in the horizontal jump, which resulted in a greater energy gain of the body's center of mass throughout the motion.</p> <p>Conclusion</p> <p>These differences in the optimal coordination strategy seem to be caused from the requirement that the body's center of mass needs to be located above the feet in a vertical jumping, whereas this requirement is not so strict in a horizontal jumping.</p

DETERMINATION OF THE OPTIMAL NUMBER OF RIGID-BODY SEGMENTS TO REPRESENT THE TRUNK USING AKAIKE’S INFORMATION CRITERION

The purpose of this study was to determine the optimal number of rigid body segments to sufficiently represent the trunk movements, using Akaike’s information criterion. The trunk in static and dynamic conditions was modelled with one, two, three, or six linked rigid-body representations. The difference in the three-dimensional position between the actual and modelled data was calculated to quantify how well these models describe the actual trunk kinematics. The Akaike’s information criterion was calculated using the difference in position data to evaluate the goodness-of-fit for each model. Our findings suggest that two-linked rigid-body representation may be good enough when analysing trunk movements except when the movement includes a large axial rotation, for which the three-linked rigid-bodies would be better. These results would be useful in determining the optimal number of rigid body representation to sufficiently represent the trunk movements

Biomechanical analysis of the relation between movement time and joint moment development during a sit-to-stand task

<p>Abstract</p> <p>Background</p> <p>Slowness of movement is a factor that may cause a decrease of quality of daily life. Mobility in the elderly and people with movement impairments may be improved by increasing the quickness of fundamental locomotor tasks. Because it has not been revealed how much muscle strength is required to improve quickness, the purpose of this study was to reveal the relation between movement time and the required muscle strength in a sit to stand (STS) task. Previous research found that the sum of the peak hip and knee joint moments was relatively invariant throughout a range of movement patterns (Yoshioka et al., 2007, Biomedical Engineering Online 6:26). The sum of the peak hip and knee joint moment is an appropriate index to evaluate the muscle strength required for an STS task, since the effect of the movement pattern variation can be reduced, that is, the results can be evaluated purely from the viewpoint of the movement times. Therefore, the sum of the peak hip and knee joint moment was used as the index to indicate the required muscle strength.</p> <p>Methods</p> <p>Experimental kinematics data were collected from 11 subjects. The time at which the vertical position of the right shoulder fell outside three standard deviations of the vertical positions during the static initial posture was regarded as the start time. The time at which the vertical position fell within three standard deviations of the vertical positions during static upright standing posture was regarded as the finish time. Each movement time of the experimental movements was linearly lengthened and shortened through post-processing. Combining the experimental procedure and the post-processing, movements having various movement patterns and a wide range of movement times were obtained. The joint moment and the static and inertial components of the joint moment were calculated with an inverse dynamics method. The static component reflects the gravitational and/or external forces, while the inertial component reflects the acceleration of the body.</p> <p>Results</p> <p>The quantitative relation between the movement time and the sum of the peak hip and knee joint moments were obtained. As the STS movement time increased, the joint moments decreased exponentially and converged to the static component (1.51 ~ 1.54 N.m/kg). When the movement time was the longest (movement time: 7.0 seconds), the joint moments (1.57 N.m/kg) closely corresponded to the minimum of 1.53 N.m/kg as reported by Yoshioka et al..</p> <p>Conclusion</p> <p>The key findings of this study are as follows. (1) The minimum required joint moment for an STS task is essentially equivalent to the static component of the joint moment. (2) For fast and moderate speed movements (less than 2.5 seconds), joint moments increased exponentially as the movement speed increased. (3) For slow movements greater than 2.5 seconds, the joint moments were relatively constant. The results of this STS research has practical applications, especially in rehabilitations and exercise prescription where improved movement time is an intended target, since the required muscle strength can be quantitatively estimated.</p

THE CHALLENEGE OF NEW APPROACHES IN BIOMECHANICS

The target of our biomechanical research is to analyze the mechanics of motion, focusing especially on the behavior of the muscle-tendon complex during dynamic human movements. In our quest to better understand human motion, we have developed the several research methodologies. In the keynote lecture, I will discuss some of the techniques we have used and what we have learned from them. Specifically I will focus on the following: 1. Ultrasonography 2. Computer Simulation 3. Optical vs Inertial Sensor Analysis

AN INTELLIGENT TREADMILL SYSTEM FOR RUNNING TRAINING: CONTROL OF BELT SPEED AND BIOFEEDBACK

We developed an intelligent treadmill system to realize more comfortable and safer running exercise. In the first part, we developed an algorithm to estimate the intended running speed of the user. We used the relation between the forward impulse of ground reaction force during the stance phase, stance time and swing time to estimate the intended running speed. We implemented the algorithm to an instrumented treadmill. In the second part, we evaluated the effects of real-time biofeedback of the mechanical stress on the legs. Initial peak of ground reaction force and leg stiffness value calculated based on the mass-spring model was visually shown. The subjects were instructed to reduce these values. It was found that initial peak of ground reaction force as well as leg stiffness can be effectively adjusted using visual biofeedback

THE EFFECT OF HIP JOINT MUSCLE STRENGTH AND SIZE ON HIP JOINT ANGULAR VELOCITY DURING 110 M HURDLING MOTION

The purpose of this study was to investigate the effect of hip joint flexor/extensor strength andsize on hip joint angular velocity during 110 m hurdling motion. To achieve this goal, we determined hip joint angular velocity during hurdling motion with high speed camera. We also measured isokinetic hip joint torque with a dynamometer, and measured the muscle volume of the psoas major muscle and hamstrings of the lead leg side with MRI. There were significant correlations between isokinetic hip joint flexor torque at 0.52 and 1.05 rad/s and hip joint flexion angular velocity (p = 0.04 and p = 0.02, respectively). There were no statistically significant correlations between muscle volume andjoint angular velocity. These results suggested that hip joint flexor strength ispossibly an important factor to swing up the lead leg quickly during hurdling motion

EFFECT OF DIFFERENT TRACK START POSITiONS ON HORIZONTAL TAKE-OFF VELOCITY OF WHOLE-SODY CENTER OF MASS IN SWIMMING: A SlMUALTION STUDY

The objective of this study was to investigate the effects of different track start positions on horizontal take-off velocity of the whole-body center of mass (COM) in swimming. The whole body was modeled as linked rigid-body segments to simulate the track start performance, and a simulation was performce with two different track start positions, with the COM positioned at the rear and low level (RL), and at the front and high level (FH). The results demonstrated that the horizontal take-off velocity was faster for the RL than the FH. The hip joint moments were larger for the RL than the FH on both front and rear legs. Therefore, the COM positioned at the rear and lower level for the track start would contribute to a greater hip joint moment generation, producing a greater horizontal velocity of the COM at take-off