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Yi-Chung Lin, Jack Farr, Kevin Carter and Benjamin J. Fregly

When optimization is used to evaluate a joint contact model's ability to reproduce experimental measurements, the high computational cost of repeated contact analysis can be a limiting factor. This paper presents a computationally-efficient response surface optimization methodology to address this limitation. Quadratic response surfaces were fit to contact quantities (contact force, maximum pressure, average pressure, and contact area) predicted by a discrete element contact model of the tibiofemoral joint for various combinations of material modulus and relative bone pose (i.e., position and orientation). The response surfaces were then used as surrogates for costly contact analyses in optimizations that minimized differences between measured and predicted contact quantities. The methodology was evaluated theoretically using six sets of synthetic (i.e., computer-generated) contact data, and practically using one set of experimental contact data. For the synthetic cases, the response surface optimizations recovered all contact quantities to within 3.4% error. For the experimental case, they matched all contact quantities to within 6.3% error except for maximum contact pressure, which was in error by up to 50%. Response surface optimization provides rapid evaluation of joint contact models within a limited range of relative bone poses and can help identify potential weaknesses in contact model formulation and/or experimental data quality.

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Jennifer Brunet, Catherine Sabiston, Andree Castonguay, Leah Ferguson and Natalia Bessette

The objectives of this study were to test the associations between physical self-discrepancies (actual:ideal and actual:ought) and physical activity behavior, and to examine whether motivational regulations mediate these associations using self-discrepancy (Higgins, 1987) and organismic integration (Deci & Ryan, 1985) theories as guiding frameworks. Young women (N = 205; M age = 18.87 years, SD = 1.83) completed self-report questionnaires. Main analyses involved path analysis using a polynomial regression approach, estimation of direct and indirect effects, and evaluation of response surface values. Agreement between actual and ideal (or ought) physical self-perceptions was related to physical activity both directly and indirectly as mediated by the motivational regulations (R 2 = .24–.30). Specifically, when actual and ideal self-perceptions scores were similar, physical activity levels increased as actual and ideal scores increased. Furthermore, physical activity levels were lower when the discrepancy was such that ideal or ought self were higher than actual self. These findings provide support for integrating self-discrepancy and organismic integration theories to advance research in this area.

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Shauna Solomon-Krakus, Catherine M. Sabiston, Jennifer Brunet, Andree L. Castonguay and Mélanie Henderson

scales ( 4 ). The way these subjective body size perceptions (agreement, direction of discrepancy, and degree of discrepancy) relate to physical activity should be explored in adolescents as this has yet to be done in the extant literature. Polynomial regression analysis with response surface methods is

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Alex J. Benson, Mark A. Eys and P. Gregory Irving

Many athletes experience a discrepancy between the roles they expect to fulfill and the roles they eventually occupy. Drawing from met expectations theory, we applied response surface methodology to examine how role expectations, in relation to role experiences, influence perceptions of group cohesion among Canadian Interuniversity Sport athletes (N = 153). On the basis of data from two time points, as athletes approached and exceeded their role contribution expectations, they reported higher perceptions of task cohesion. Furthermore, as athletes approached and exceeded their social involvement expectations, they reported higher perceptions of social cohesion. These response surface patterns—pertaining to task and social cohesion—were driven by the positive influence of role experiences. On the basis of the interplay between athletes’ role experiences and their perception of the group environment, efforts to improve team dynamics may benefit from focusing on improving the quality of role experiences, in conjunction with developing realistic role expectations.

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Nikos L. D. Chatzisarantis, Vassilis Barkoukis, Panagiotis Petridis, Cecilie Thøgersen-Ntoumani, Nikos Ntoumanis, Sandra Gountas, John Gountas, Dimitrios Adam and Martin S. Hagger

Previous research documented that “extremely high prioritization” strategies that involved allocation of all resources for time or energy on pursuing goals related to leisure-time physical activity and none of available resources on competing behavioral goals were optimal in terms of yielding highest levels of participation in physical activities. This study examined whether a “marginally higher prioritization” strategy that involved an intention to invest large but slightly more resources on physical activity than competing behaviors was optimal. In addition, we examined whether linear and quadratic models supported different conclusions about optimal prioritizations strategies. Response surface analyses of a quadratic model revealed that marginally higher prioritization was the most effective strategy. In addition, a linear regression model led us to incorrectly reject a “simultaneous goal pursuit” strategy in favor of an extremely high prioritization strategy. Findings suggest that prioritization strategies that “garner” low opportunity costs are the most optimal.

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Jeremy J. Bauer, Robyn K. Fuchs, Gerald A. Smith and Christine M. Snow

Drop landings increase hip bone mass in children. However, force characteristics from these landings have not been studied. We evaluated ground and hip joint reaction forces, average loading rates, and changes across multiple trials from drop landings associated with osteogenesis in children. Thirteen prepubescent children who had previously participated in a bone loading program volunteered for testing. They performed 100 drop landings onto a force plate. Ground reaction forces (GRF) and two-dimensional kinematic data were recorded. Hip joint reaction forces were calculated using inverse dynamics. Maximum GRF were 8.5 ± 2.2 body weight (BW). At initial contact, GRF were 5.6 ± 1.4 BW while hip joint reactions were 4.7 ± 1.4 BW. Average loading rates for GRF were 472 ± 168 BW/s. Ground reaction forces did not change significantly across trials for the group. However, 5 individuals showed changes in max GRF across trials. Our data indicate that GRF are attenuated 19% to the hip at the first impact peak and 49% at the second impact peak. Given the skeletal response from the drop landing protocol and our analysis of the associated force magnitudes and average loading rates, we now have a data point on the response surface for future study of various combinations of force, rate, and number of load repetitions for increasing bone in children.

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Kanehisa 1 and Tetsuo Fukunaga 4 5 2006 22 2 112 119 10.1123/jab.22.2.112 Response Surface Optimization for Joint Contact Model Evaluation Yi-Chung Lin 1 Jack Farr 3 Kevin Carter 4 Benjamin J. Fregly 1 2 5 2006 22 2 120 130 10.1123/jab.22.2.120 Review Biomechanical Behavior of Muscle