optimal force chosen in this research was established from performing a sensitivity analysis on the influence of the optimal force value on outputs (using values of 10, 50, 75, 100, 150, 200, and 1000 N). Generalized forces at the joint are calculated as follows: ∑ m = 1 n [ a m f ( F m 0 , l m , v m
Amy R. Lewis, William S.P. Robertson, Elissa J. Phillips, Paul N. Grimshaw and Marc Portus
The purpose of this study was twofold: (a) to investigate the effect of the method of body segment parameter (BSP) estimation on the accuracy of the experimental simulation of a complex airborne movement; and (b) to assess the applicability of selected BSP estimation methods in the experimental simulation. It was hypothesized that different BSP estimation methods would provide different simulation results. A sensitivity analysis was performed to identify the BSP items and segments responsible for the inter-method differences in the simulation accuracy. The applicability of the estimation methods was assessed based on the simulation results and the number of anthropometric parameters required. Ten BSP estimation methods classified into 3 groups (4 cadaver-based, 4 gamma mass scanning-based, and 2 geometric) were employed in a series of experimental simulations based on 9 double-somersault-with-full-twist H-bar dismounts performed by 3 male college gymnasts. The simulated body orientation angles were compared with the corresponding observed orientation angles in computing the simulation errors. The inclination and twist simulation errors revealed significant (p < .05) differences among the BSP estimation groups and methods. It was concluded that: (a) the method of BSP estimation significantly affected the simulation accuracy, and more individualized BSP estimation methods generally provided more accurate simulation results; (b) the mass items, and the lower leg and thorax/ abdomen were more responsible for the intermethod differences in the simulation accuracy than other BSP items and segments, respectively; (c) the ratio methods and the simple regression methods were preferable in simulation of the somersaulting motion due to the fewer anthropometric parameters required; (d) the geometric models and the cadaver-based stepwise regression method were superior to the other methods in the simulation of the complex airborne motion with twist.
Li-Xin Guo, Zhao-Wen Wang, Yi-Min Zhang, Kim-Kheng Lee, Ee-Chon Teo, He Li and Bang-Chun Wen
The aim of this study is to investigate the effect of material property changes in the spinal components on the resonant frequency characteristics of the human spine. Several investigations have reported the material property sensitivity of human spine under static loading conditions, but less research has been devoted to the material property sensitivity of spinal biomechanical characteristics under a vibration environment. A detailed three-dimensional finite element model of the human spine, T12– pelvis, was built and used to predict the influence of material property variation on the resonant frequencies of the human spine. The simulation results reveal that material properties of spinal components have obvious influences on the dynamic characteristics of the spine. The annulus ground substance is the dominant component affecting the vertical resonant frequencies of the spine. The percentage change of the resonant frequency relative to the basic condition was more than 20% if Young’s modulus of disc annulus is less than 1.5 MPa. The vertical resonant frequency may also decrease if Poisson’s ratio of nucleus pulposus of intervertebral disc decreases.
Matthew T.G. Pain and John H. Challis
Wobbling mass models have been used to gain insight into joint loading during impacts. This study investigated the sensitivity of a wobbling mass model of landing from a drop to the model's parameters. A 2-D 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 nonlinear 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 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. Model simulations were relatively insensitive to variations in the properties of the connection between wobbling masses and the skeleton. If the goal is to examine the effects of wobbling mass on the system, this insensitivity is an advantage, with the proviso that estimates for the other model parameters and joint torque activation timings lie in a realistic range. If precise knowledge about the motion of the wobbling mass is of interest, however, this calls for more experimental work to precisely determine these model parameters.
David A. White, Youngha Oh and Erik A. Willis
. Not surprisingly, our sensitivity analysis revealed some differences in outcomes depending on which cut point and MET value for MVPA were applied, suggesting that not all MVPA cut points are the same and may provide different outcomes The Freedson/Saint-Maurice cut points also showed a significant
Gonzalo A. Bravo, Doyeon Won and Mauricio Ferreira
Trade-offs in consumer choice become central to understanding how choice actually occurs. This study examines the trade-offs sport management students are willing to make in order to select the program of their choice. Sport management undergraduate students (N = 498) participated in a full-profile conjoint experiment asking them to rate 18 program-choice scenarios resulted from the factorial design of seven attributes and nineteen levels. Results at the aggregated level indicated that program environment was the most important attribute in choosing a sport management graduate program, followed by program reputation, graduate assistantship, cost/tuition, NCAA affiliation, program length, and location. Given these results, a sensitivity analysis illustrated that students were willing to make trade-offs among program characteristics, particularly pay more for a program with better reputation. Results from the current study are valuable and informative for sport management programs for setting market boundaries and selecting what to promote when advertising to attract prospective students.
Russell J. Best, Roger M. Bartlett and Richard A. Sawyer
This paper reports a study of the optimal release of men's and women's new and old rule javelins involving modeling, simulation, optimization (including sensitivity analysis), and simulation evaluation. Because of the lack of repro-ducibility in earlier results of two-dimensional flight simulation research, the paper presents a continuation of the two-dimensional model used previously. As expected, each javelin was found to have a different optimal release for a given individual, and the optimal release varied with the thrower's nominal release speed. A limited degree of simulation evaluation was achieved by comparison of the model and simulation results with measured throws. Within the constraints of measurement error, this tended to support both the adequacy of the two-dimensional model and the results of the simulations for such high standard throws. However, further experimental studies to quantify the angle of yaw (sideslip) in measured wind conditions are recommended to assess any changes needed to the two-dimensional model of javelin throwing and to determine the advisability of including this three-dimensional aspect of javelin release in future simulations.
Marc A. Adams, Sherry Ryan, Jacqueline Kerr, James F. Sallis, Kevin Patrick, Lawrence D. Frank and Gregory J. Norman
Concurrent validity of Neighborhood Environment Walkability Scale (NEWS) items was evaluated with objective measures of the built environment using geographic information systems (GIS).
A sample of 878 parents of children 10 to 16 years old (mean age 43.5 years, SD = 6.8, 34.8% non-White, 63.8% overweight) completed NEWS and the International Physical Activity Questionnaire. GIS was used to develop 1-mile street network buffers around participants’ residences. GIS measures of the built environment within participants’ buffers included percent of commercial and institutional land uses; number of schools and colleges, recreational facilities, parks, transit stops, and trees; land topography; and traffic congestion.
Except for trees and traffic, concordance between the NEWS and GIS measures were significant, with weak to moderate effect sizes (r = −0.09 to −0.36, all P ≤ 01). After participants were stratified by physical activity level, stronger concordance was observed among active participants for some measures. A sensitivity analysis of self-reported distance to 15 neighborhood destinations found a 20-minute (compared with 10- or 30-minute) walking threshold generally had the strongest correlations with GIS measures.
These findings provide evidence of the concurrent validity of self-reported built environment items with objective measures. Physically active adults may be more knowledgeable about their neighborhood characteristics.
Michele LeBlanc and Jesús Dapena
Equations that clarify the mechanical relationships between various parameter values and the velocity of the distal endpoint of a two-segment kinetic chain modeling the human arm were developed and analyzed. In particular, a single equation was presented that relates the distal endpoint velocity to the system’s angular momentum (as an indicator of muscular torque input), the ratio of the distal segment’s angular velocity to that of the proximal segment (the flail ratio), and the angle between the two segments (the configuration angle). These three system variables were analyzed to examine which values are best for creating a large value for the velocity of the distal endpoint. In addition, a sensitivity analysis was conducted to determine whether the relationships between the system values and the distal endpoint velocity were consistent for varying segment parameters. The relationships found were consistent for the various segment parameters. For any given values of the flail ratio and the configuration angle, the larger the value of the system angular momentum, the larger the value of the distal endpoint velocity. For any given values of the system angular momentum and the configuration angle, the larger the flail ratio, the larger the value of the distal endpoint velocity. For given values of the system angular momentum and the flail ratio, the optimal configuration angle that maximizes the distal endpoint velocity depends on the flail ratio value. While it may be impossible to generate simultaneously the combination of optimal parameter values determined, the knowledge of the relationships of these parameters with each other and with the distal endpoint velocity will aid in the search for an attainable optimal compromise.
Nikita Rowley, James Steele, Matthew Wade, Robert James Copeland, Steve Mann, Gary Liguori, Elizabeth Horton and Alfonso Jimenez
model was 676 MET minutes per week (539–812 min, P < .0001). Figure 2 shows the forest plot for pre-ERS MET minutes. Significant heterogeneity was evident among the schemes ( Q (11) = 84.31, P <.0001; I 2 = 90.41%), however, the sensitivity analysis did not reveal any influential schemes