Guangyu Liu

Contributions of joint rotations to ball release speed during cricket bowling: A three-dimensional kinematic analysis

Abstract The purpose of this study was to discover the contributions of individual upper body segmental rotations to ball release speed for cricket bowling and determine whether attempting to forcefully flex the lower trunk leads to an increase in ball release speed and bowling accuracy. Three dimensional kinematic data of eight male fast bowlers were recorded by a Vicon motion capture system under three cricket bowling conditions: (1) participants bowled at their stock delivery speeds (sub-max condition), (2) participants bowled at their absolute maximal speeds (max condition), and (3) participants bowled at their absolute maximal speeds but forced to flex the lower trunk (max-trunk condition). The accuracy of each delivery was also measured. The results showed that the average ball release speeds for the max-trunk condition were faster than the other two conditions. A general pattern of proximal to distal sequencing was observed for all three conditions. There was a slight decrement in accuracy seen in the max-trunk condition with respect to the other two conditions. For all three conditions, the upper arm rotation made the largest contribution, followed in turn by torso and thorax rotation, pelvis rotation, linear velocity of pelvis, and forearm and hand rotation.

Optimization of Spring-Loaded Crutches via Boundary Value Problem

The objective of the work is to optimize the design of spring-loaded crutches by choosing appropriate spring stiffness based on their dynamic characteristics. It was shown in the literature that ambulation with spring-loaded crutches reduces the initial impulse yielded by ambulation with standard crutches and provides a propulsion mechanism. This research not only provides a genre of the spring-loaded crutches via compliance, but also proposes an approach to optimize the stiffness of the helical spring through studying the dynamics of crutch stance. The method is developed using a boundary value problem and its solution method and is studied numerically. Experiments were carried out on four subjects in a biomechanics laboratory. It suggests that the optimized spring-loaded crutches guarantee the propulsion mechanism at the right time and right position during dynamical ambulation.

Biomechanical Evaluation of an Innovative Spring-Loaded Axillary Crutch Design

ABSTRACT We evaluated an innovative spring-loaded crutch design by comparing its performance with standard crutches through a biomechanical approach. Gait analysis was conducted for 7 male subjects under two conditions: walking with standard crutches and with spring-loaded crutches. Three-dimensional kinematic data and ground reaction force were recorded. Spatiotemporal variables, external mechanical work, and elastic energy (for spring crutches) were calculated based on recorded data. The trajectories of vertical ground reaction forces with standard crutches had two main peaks before and after mid-stance, and those with optimized spring-loaded crutches had only one main peak. The magnitude of external mechanical work was significantly higher with spring-loaded crutches than with standard crutches for all subjects, and the transferred elastic energy made an important contribution to the total external work for spring-loaded crutches. No significant differences in the spatiotemporal parameters were observed. Optimized spring-loaded crutches can efficiently propel crutch walkers and could reduce the total energy expenditure in crutch walking. Further research using optimized spring-loaded crutches with respect to energy efficiency is recommended.

Mechanical Efficiency of Walking with Spring-loaded Axillary Crutches

ABSTRACT The objective of this study was to investigate the effect of using spring-loaded crutches on mechanical efficiency in comparison to the use of standard crutches. Seven healthy male participants were recruited for this experiment. They were instructed to walk around a track on two types of crutches for five minutes under four controlled conditions. Ground reaction force and motion trajectories were recorded, which were used to calculate mechanical energy expenditure. Simultaneously, portable gas analysis machinery was used to collect the metabolic parameters of participants, in order to determine mechanical efficiency, the ratio of mechanical energy expenditure to metabolic energy expenditure. It was found that the mechanical efficiency was significantly higher when participants walked with spring-loaded crutches than when they walked with standard crutches. There were no significant differences in metabolic energy expenditure between the spring-loaded crutch conditions and standard crutch conditions.

Biomechanical simulation of anterior cruciate ligament strain for sports injury prevention

The purpose of this study was to quantify in vivo anterior cruciate ligament (ACL) strain by computer simulation, which includes a marker-based biomechanical model and a skeletal geometry model. Kinematic data collected by a motion capture system was used as the input and ACL strain during the movement time period was the output. Case studies were conducted to simulate ACL strain during jump landing, running and sidestep cutting activities. The simulation results were analysed and compared with previous findings in literature. The results show that the simulation is a useful tool in understanding ACL injury mechanisms related to sports activities.

Pole vault performance for anthropometric variability via a dynamical optimal control model.

Optimal performance of a dynamical pole vault process was modeled as a constrained nonlinear optimization problem. That is, given a vaulters anthropomorphic data and approach speed, the vaulter chose a specific take-off angle, pole stiffness and gripping height in order to yield the greatest jumping height compromised by feasible bar-crossing velocities. The optimization problem was solved by nesting a technique of searching an input-to-output mapping arising from the vaulting trajectory and a method of nonlinear sequential quadratic programming (SQP). It was suggested from the optimization results that the bodys weight has an important influence on the vaulting performance beside the vaulters height and approach speed; the less skilled vaulter should gradually adopt a longer pole to improve the performance.

Lumbar spinal loading during bowling in cricket: a kinetic analysis using a musculoskeletal modelling approach.

ABSTRACT The objective of the study was to evaluate two types of cricket bowling techniques by comparing the lumbar spinal loading using a musculoskeletal modelling approach. Three-dimensional kinematic data were recorded by a Vicon motion capture system under two cricket bowling conditions: (1) participants bowled at their absolute maximal speeds (max condition), and (2) participants bowled at their absolute maximal speeds while simultaneously forcing their navel down towards their thighs starting just prior to ball release (max-trunk condition). A three-dimensional musculoskeletal model comprised of the pelvis, sacrum, lumbar vertebrae and torso segments, which enabled the motion of the individual lumbar vertebrae in the sagittal, frontal and coronal planes to be actuated by 210 muscle-tendon units, was used to simulate spinal loading based on the recorded kinematic data. The maximal lumbar spine compressive force is 4.89 ± 0.88BW for the max condition and 4.58 ± 0.54BW for the max-trunk condition. Results showed that there was no significant difference between the two techniques in trunk moments and lumbar spine forces. This indicates that the max-trunk technique may not increase lower back injury risks. The method proposed in this study could be served as a tool to evaluate lower back injury risks for cricket bowling as well as other throwing activities.

The optimal event-based control of parachute opening problem II: A case study

We propose an finite time optimal event-based controller associated with an optimized strategy of parachute air drop in a rescue mission in order to minimize the drop interval to ensure a fast and accurate landing while a safe landing speed must be guaranteed. The idea is to determine an optimal instant to trigger the event-based controller. The design takes several steps to simplify the optimization via the tools of integration, penalty function and steepest descent algorithm. The result shows that the proposed controller yields the best performance among the non-optimized ones.

The optimal event-based control of parachute opening problem I: Theory

We propose an event-based controller associated with an optimized strategy of parachute air drop. In a rescue mission or combat, it is important to minimize the drop interval to ensure a fast and accurate landing while a safe landing speed must be guaranteed. Opening the parachute timely is viewed as an optimal event-based control problem. The idea of optimal event-based control design is to identify the key event of the hybrid dynamics where a supervisor triggers the event-based controller at a right time. Perfect timing is given by a particular nonlinear optimization problem. To this end, we propose a method that takes a couple of steps to simplify the optimization via the tools of integration, penalty function and steepest descent algorithm. The method can be used to a range of applications: such as diaster rescue, combat, and space device recycling.

Biomechanics of innovative spring-loaded axillary crutches

The aim was to evaluate an innovative spring-loaded crutch design by comparing its performance with standard crutches through a biomechanical approach. Gait analysis was conducted for 7 male subjects under two conditions: walking with standard crutches and with spring-loaded crutches. Three dimensional kinematic data and ground reaction force were recorded. Spatiotemporal variables, external mechanical work and elastic energy (for spring crutches) were calculated based on recorded data. The magnitude of external mechanical work was significantly higher with spring-loaded crutches than with standard crutches for all subjects and the transferred elastic energy made an important contribution to the total external work for spring-loaded crutches. No significant differences of the spatiotemporal parameters were observed. Optimized spring-loaded crutches can efficiently propel the crutch walker and could reduce the total energy expenditure in crutch walking. Further research using optimized spring-loaded crutches with respect to energy efficiency is recommended.