Do stiffness and asymmetries predict change of direction performance?

Change of direction speed (CODS) underpins performance in a wide range of sports but little is known about how stiffness and asymmetries affect CODS. Eighteen healthy males performed unilateral drop jumps to determine vertical, ankle, knee and hip stiffness, and a CODS test to evaluate left and right leg cutting performance during which ground reaction force data were sampled. A step-wise regression analysis was performed to ascertain the determinants of CODS time. A two-variable regression model explained 63% (R-2 = 0.63; P = 0.001) of CODS performance. The model included the mean vertical stiffness and jump height asymmetry determined during the drop jump. Faster athletes (n = 9) exhibited greater vertical stiffness (F = 12.40; P = 0.001) and less asymmetry in drop jump height (F = 6.02; P = 0.026) than slower athletes (n = 9); effect sizes were both "large" in magnitude. Results suggest that overall vertical stiffness and drop jump height asymmetry are the strongest predictors of CODS in a healthy, non-athletic population

The effect of joint compliance within rigid whole-body computer simulations of impacts

In high impact human activities, much of the impact shock wave is dissipated through internal body structures, preventing excessive accelerations from reaching vital organs. Mechanisms responsible for this attenuation, including lower limb joint compression and spinal compression have been neglected in existing whole-body simulation models. Accelerometer data on one male subject during drop landings and drop jumps from four heights revealed that peak resultant acceleration tended to decrease with increasing height in the body. Power spectra contained two major components, corresponding to the active voluntary movement (2 Hz 14 Hz) and the impact shock wave (16 Hz 26 Hz). Transfer functions demonstrated progressive attenuation from the MTP joint towards the C6 vertebra within the 16 Hz 26 Hz component. This observed attenuation within the spine and lower-limb joint structures was considered within a rigid body, nine-segment planar torque-driven computer simulation model of drop jumping. Joints at the ankle, knee, hip, shoulder, and mid-trunk were modelled as non-linear spring-dampers. Wobbling masses were included at the shank, thigh, and trunk, with subject-specific biarticular torque generators for ankle plantar flexion, and knee and hip flexion and extension. The overall root mean square difference in kinetic and kinematic time-histories between the model and experimental drop jump performance was 3.7%, including ground reaction force root mean square differences of 5.1%. All viscoelastic displacements were within realistic bounds determined experimentally or from the literature. For an equivalent rigid model representative of traditional frictionless pin joint simulation models but with realistic wobbling mass and foot-ground compliance, the overall kinetic and kinematic difference was 11.0%, including ground reaction force root mean square differences of 12.1%. Thus, the incorporation of viscoelastic elements at key joints enables accurate replication of experimentally recorded ground reaction forces within realistic whole-body kinematics and removes the previous need for excessively compliant wobbling masses and/or foot-ground interfaces. This is also necessary in cases where shock wave transmission within the simulation model must be non-instantaneous

From standing posture to vertical jump - Experimental and model analysis of human movement

Dalla postura eretta al salto verticale - Analisi sperimentale e modellistica del movimento uman

A PILOT STUDY OF THE KNEE JOINT ACTION CONTRIBUTIONS TO LOADING IN LANDINGS PERFORMED BY FEMALES

Females are particularly susceptible to knee injuries in landing. This investigation aimed to gain further insight into the contributions of female knee joint actions to loading in landing. A wobbling mass model was used to simulate landings executed with a self-selected strategy. The selected knee actions were modified and the resulting loads were examined. A 0.05 s change in knee joint action timing substantially increased the peak vertical ground reaction force (GFz) by 1.55 BW. Conversely, a small reduction in peak GFz (0.06 BW) was produced using a 10 % more extended knee during the impact. The prominent influence the knee joint action timing had on loading may be attributed to the need to maintain coordinated and continuous load attenuation. Subject-specific modifications to landing strategies were found to achieve load reductions

ISBS 2018 AUCKLAND CONFERENCE SCHEDULE FINAL

This document contains the ISBS 2018 Auckland Conference Schedule of keynotes, oral podiums, oral posters, social events, workshops, SPRINZ-HPSNZ-AUT Millennium applied half day and teachers day

Condensation And Mobility Studies Of Fluid Interfaces

Condensation is of central importance in a broad range of areas in nature and industry. Aerosol-cloud interactions, a currently a significant open question in climate modeling, and water harvesting mechanisms on organisms such as cacti, beetles, and spiders, are natural processes that are rely on condensation. Condensation is an effective method for transferring heat due to the latent heat required for a fluid to change phase from a gas to a liquid. Improvements in condensation processes would have an impact in a variety of industrial areas such as thermal management, environmental control, microelectronics, desalination, and power generation. Dropwise condensation is preferable over filmwise condensation because it has a significantly higher heat transfer coefficient. Nanopatterned surfaces are of interest because they have experimentally demonstrated higher heat transfer than their smooth counterparts, but recent heat transfer measurements on individual droplets have revealed discrepancies between theoretical predictions and experimental measurements for the smallest droplets. Interfacial properties on small length scales are often difficult to measure experimentally and are often used as fitting parameters in condensation models. The common assumptions used when modeling dropwise condensation are that (1) the condensing droplets are thermodynamically quasi-static and that (2) the heat and mass transport are uncoupled, that is, droplet motion and heat transfer are modeled independently of one another. In this dissertation, several continuum properties including the mass accommodation coefficient and interfacial mobility are computed allowing for the physical parameters to be known a priori for continuum scale models such as the Navier-Stokes-Cahn-Hilliard equations or interfacial resistances in condensation models. Furthermore, the two fundamental assumptions used in condensation models are examined in an attempt to resolve the theoretical and experimental discrepancies. This will be done by leveraging microscopic and nonequilibrium thermodynamic approaches to determine the validity of the condensation assumptions for planar and highly curved systems