474 research outputs found
Detection of long-range dependence in peak ground reaction forces during running using ARFIMA modelling
Complexity of isometric force production is associated with time to achieve steady state when moving to a new force level.
Estimating individual muscle forces in human movement
If individual muscle forces could be routinely calculated in vivo, non-invasively, considerable insight could
be obtained into the etiology of injuries and the training of muscle for rehabilitation and sport. As there are
generally more muscles crossing a joint than there are degrees of freedom at the joint, determining the
individual forces in the muscles crossing a joint is a non-trivial problem. This study focused on the
development of the procedures necessary to estimate the individual muscle forces during a dumbell curl,
and the measurement procedures required for the determination of the necessary input parameters. The
procedures developed could easily be applied to other body movements. [Continues.
Theory of preparation and relaxation of a p-orbital atomic Mott insulator
We develop a theoretical framework to understand the preparation and
relaxation of a metastable Mott insulator state within the first excited band
of a 1D optical lattice. The state is loaded by "lifting" atoms from the ground
to the first excited band by means of a stimulated Raman transition. We
determine the effect of pulse duration on the accuracy of the state preparation
for the case of a Gaussian pulse shape. Relaxation of the prepared state occurs
in two major stages: double-occupied sites occurring due to quantum
fluctuations initially lead to interband transitions followed by a spreading of
particles in the trap and thermalization. We find the characteristic relaxation
times at the earliest stage and at asymptotically long times approaching
equilibrium. Our theory is applicable to recent experiments performed with 1D
optical lattices [T. M\"uller, S. F\"olling, A. Widera, and I. Bloch, Phys.
Rev. Lett. \textbf{99}, 200405 (2007)].Comment: 27 pages, 23 figures: Edited figures, added reference
Soft tissue motion influences skeletal loads during impacts
Soft tissue motion occurs as impulsive loads are applied to the skeletal system. It has been
demonstrated that the wave like motion of these wobbling masses can reduce the loads acting on the
musculoskeletal system. This is an important concept to consider, whether the loads acting on the
musculoskeletal system are being determined using either inverse or direct dynamics
The influence of soft tissue movement on ground reaction forces, joint torques and joint reaction forces in drop landings
The aim of this study was to determine the effects that soft tissue motion has on ground reaction forces, joint torques and joint reaction forces in drop landings. To this end a four body-segment wobbling mass model was developed to reproduce the vertical ground reaction force curve for the first 100 ms of landing. Particular attention was paid to the passive impact phase, while selecting most model parameters a priori, thus permitting examination of the rigid body assumption on system kinetics. A two-dimensional wobbling mass model was developed in DADS (version 9.00, CADSI) to simulate landing from a drop of 43 cm. Subject specific inertia parameters were calculated for both the rigid links and the wobbling masses. The magnitude and frequency response of the soft tissue of the subject to impulsive loading was measured and used as a criterion for assessing the wobbling mass motion. The model successfully reproduced the vertical ground reaction force for the first 100 ms of the landing with a peak vertical ground reaction force error of 1.2 % and root mean square errors of 5% for the first 15 ms and 12% for the first 40 ms. The resultant joint forces and torques were lower for the wobbling mass model compared with a rigid body model, up to nearly 50% lower, indicating the important contribution of the wobbling masses on reducing system loading
Wobbling mass influence on impact ground reaction forces: A simulation model sensitivity analysis
To gain insight into joint loadings during impacts, wobbling mass models have been used. The
aim of this study was to investigate the sensitivity of a wobbling mass model, of landing from a
drop, to the model's parameters. A two-dimensional wobbling mass model was developed. Three
rigid linked segments designed to represent the skeleton each had a second mass attached to them,
via two translational non-linear spring dampers, representing the soft tissue. Model parameters
were systematically varied one at a time and the effect this had on the peak vertical ground
reaction force and segment kinematics was examined. Model output showed low sensitivity to
most model parameters but was sensitive to the timing of joint torque initiation. Varying the heel
pad stiffness in the range of stiffness values reported in the literature had the largest influence on
the peak vertical ground reaction force. The analysis indicated that the more proximal body
segments had a lower influence on peak vertical ground reaction force per unit mass than the
segments nearer the contact point, 340 N/kg, 157 N/kg and 24 N/kg for the shank, thigh and trunk
respectively. Model simulations were relatively insensitive to variations in the properties of the
connection between the wobbling masses and the skeleton. Given the proviso that estimates for
the other model parameters and joint torque activation timings lie in a realistic range, then if the
goal is to examine the effects of the wobbling mass on the system this insensitivity is an
advantage. If precise knowledge about the motion of the wobbling mass is of interest, however,
more experimental work is required to determine precisely these model parameters
The role of the heel pad and shank soft tissue during impacts: a further resolution of a paradox
The aim of this study was to test the hypothesis that by accounting for soft tissue motion of the lower leg during the impacts associated with in vivo testing, that the differences between in vivo and in vitro estimates of heel pad properties can be explained. To examine this a two-dimensional model of the shank and heel pad was developed using DADS. The model contained a heel pad element and a rigid skeleton to which was connected soft tissue which could move relative to the bone. Simulations permitted estimation of heel pad properties directly from heel pad deformations, and from the kinematics of an impacting pendulum. These two approaches paralleled those used in vitro and in vivo respectively. Measurements from the pendulum indicated that heel pad properties changed from those found in vitro to those found in vivo as relative motion of the bone and soft tissue was allowed. This would indicate that pendulum measures of the in vivo heel pad properties are also measuring the properties of the whole lower leg. The ability of the wobbling mass of the shank to dissipate energy during an impact was found to be significant. These results demonstrate the important role of both the heel pad and soft tissue of the shank to the dissipation of mechanical energy during impacts. These results provide a further clarification of the paradox between the measurements of heel pad properties made in vivo and in vitro
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