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Nicholas A. Vavalle, A. Bradley Thompson, Ashley R. Hayes, Daniel P. Moreno, Joel D. Stitzel, and F. Scott Gayzik

Accurate mass distribution in computational human body models is essential for proper kinematic and kinetic simulations. The purpose of this study was to investigate the mass distribution of a 50th percentile male (M50) full body finite element model (FEM) in the seated position. The FEM was partitioned into 10 segments, using segment planes constructed from bony landmarks per the methods described in previous research studies. Body segment masses and centers of gravity (CGs) of the FEM were compared with values found from these studies, which unlike the present work assumed homogeneous body density. Segment masses compared well to literature while CGs showed an average deviation of 6.0% to 7.0% when normalized by regional characteristic lengths. The discrete mass distribution of the FEM appears to affect the mass and CGs of some segments, particularly those with low-density soft tissues. The locations of the segment CGs are provided in local coordinate systems, thus facilitating comparison with other full body FEMs and human surrogates. The model provides insights into the effects of inhomogeneous mass on the location of body segment CGs.

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Jeremy D. Smith and Philip E. Martin

Unilateral, transtibial amputees exhibit walking asymmetries and higher metabolic costs of walking than nonamputees walking at similar speeds. Using lightweight prostheses has previously been suggested as a contributing factor to walking asymmetries. The purpose was to investigate the effects of prosthesis mass and mass distribution on metabolic costs and walking asymmetries among six unilateral, transtibial amputees. Kinematic and temporal symmetry did not improve when mass was added at different locations on the limb. Stance and swing time asymmetries increased by 3.4% and 7.2%, respectively, with loads positioned distally on the limb. Maximum knee angular velocity asymmetries increased by 6% with mass added to the thigh, whereas maximum thigh angular velocity asymmetries increased by approximately 10% with mass positioned near the prosthetic ankle. Adding 100% of the estimated mass difference between intact and prosthetic legs to the ankle of the prosthesis increased energy costs of walking by 12%; adding the same mass to the prosthesis center of mass or thigh center of mass increased metabolic cost by approximately 7% and 5%, respectively. Unless other benefits are gained by increasing prosthesis mass, this should not be considered as a possible alternative to current lightweight prosthesis designs currently being prescribed to unilateral amputees.

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Marianne J.R. Gittoes and David G. Kerwin

A modification to an existing mathematical model is described, which permits the determination of subject-specific inertia parameters for wobbling and rigid masses of female body segments. The model comprises segment-specific soft tissue, bone, and lung components. A total of 59 geometric solids (40 soft tissue, 17 bone, 2 lung) were used to represent the body components. Ninety-five anthropometric measurements were collected from 7 female participants and were used to develop and evaluate the model. The success of the model is evaluated using predicted mass and mass distribution. The overall absolute accuracy in predicted whole body mass was better than 3.0%, with a maximum error of 4.9%. The appropriateness of the cadaver-based density values used in the model is addressed and the accuracy of the component inertia model in relation to uniform density models is discussed. The model offers a novel approach for determining component inertia parameters, which have been used successfully in a wobbling mass model to produce realistic kinetic analyses of drop-landings.

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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.

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Hiromasa Ueno, Tadashi Suga, Kenji Takao, Masafumi Terada, Akinori Nagano, and Tadao Isaka

our knowledge, no other studies have examined the relationship between trunk segment mass and running performance in endurance runners. Therefore, the present study is the first to determine that a mass distribution with smaller leg mass and greater trunk mass may be advantageous for achieving better

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Brenda Lindstrom, Karen Chad, Nigel Ashworth, Bobbi Dunphy, Elizabeth Harrison, Bruce Reeder, Sandi Schultz, Suzanne Sheppard, and Kori Fisher

Background:

Engaging sedentary individuals in physical activity (PA) is challenging and problematic for research requiring large, representative samples. For research projects to be carried out in reasonable timeframes, optimum recruitment methods are needed. Effective recruitment strategies involving PA interventions for older adults have not been determined.

Purpose:

To compare the effectiveness of recruitment strategies for a PA intervention.

Methods:

Two recruitment strategies, print media and personal contact, targeted health-care professionals and the general public.

Results:

The strategies generated 581 inquiries; 163 were randomized into the study. Advertising to the general public via print materials and group presentations accounted for 78% of the total inquiries. Referrals from physicians and health-care professionals resulted in 22% of the inquiries.

Conclusion:

Mass distribution of print material to the general public, enhanced by in-person contact, was the most effective recruitment strategy. These findings suggest various recruitment strategies targeting the general population should be employed.

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Jasper Reenalda, Maurice T.F. Maas, and Jos J. de Koning

Purpose:

To examine the influence of induced changes in the morphology of the leg by adding mass on the optimal step length (OSL) in experienced runners to get more insight into parameters that influence preferred step length (PSL) and OSL.

Methods:

Thirteen experienced male runners (mean age 26.9 ± 6.1 y, height 183.7 ± 7.1 cm, mass 71.8 ± 5.9 kg) ran on a treadmill in 3 different conditions: unloaded (UL), loaded with 2 kg mass at the ankles (MA), and loaded with 2 kg mass at the hips (MH) at 7 different step lengths (SLs). SL deviations were expressed as deviations in relative leg length (%LL) from the individual PSL: 0%LL, ±5%LL, ±10%LL, and ±15%LL. Trials lasted 8 min, and 8 min of rest was given between trials. Oxygen uptake (V̇O2) was expressed as a fraction of V̇O2 at PSL + 0%LL in the unloaded condition (%V̇O2). The %SL with the lowest value of %V̇O2 was considered the OSL for this group of participants.

Results:

OSL at the UL condition was 6% shorter than PSL. The MA condition resulted in a 7%LL larger OSL than at UL and MH (P < .05).

Conclusions:

The mass distribution of the leg is a determinant of the OSL. As a consequence of the added mass to the ankles, OSL was 7%LL longer. Morphological characteristics of the leg might therefore play an important role in determining the runner’s individual optimal SL.

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Gislaine S. Kogure, Cristiana L. Miranda-Furtado, Daiana C.C. Pedroso, Victor B. Ribeiro, Matheus C. Eiras, Rafael C. Silva, Lisandra C. Caetano, Rui A. Ferriani, Rodrigo T. Calado, and Rosana M. dos Reis

Background: Physical activity is prescribed as a component of primary management for polycystic ovary syndrome (PCOS). This nonrandomized, therapeutic, open, single-arm study investigated the effects of progressive resistance training (PRT) on obesity indices in women with PCOS, and the relationship between obesity indices and telomere content. Methods: A total of 45 women with PCOS and 52 with non-PCOS (controls), aged 18 to 37 years, with body mass indexes of 18 to 39.9 kg/m2, performed three 1-hour sessions of PRT per week, for 16 weeks. Before and after PRT, measures included anthropometric indices and regions of interest of fat mass distribution, quantified by dual-energy X-ray absorptiometry, metabolic and hormonal parameters, and telomere content. The general linear mixed models were used to determine the effects of PRT. Results: PRT did reduce the waist-to-height ratio, waist circumference, and the index of conicity among PCOS (P < .01). However, PRT did not influence regions of interest, body mass index, and WHR. After PRT, the telomere content was associated with regions of interest and anthropometric indices in whole group independent of PCOS (P < .05). Conclusion: Resistance exercise improves obesity indices in PCOS, independent of changes in body weight, and the relationship between telomeres and obesity parameters in PCOS remain to be fully clarified.

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Matthew T.G. Pain and John H. Challis

This study had two purposes: to evaluate a new method for measuring segmental dimensions for determining body segment inertial parameters (BSIP), and to evaluate the changes in mass distribution within a limb as a consequence of muscular contraction. BSIP were calculated by obtaining surface data points of the body under investigation using a sonic digitizer, interpolating them into a regular grid, and then using Green’s theorem which relates surface to volume integrals. Four skilled operators measured a test object; the error was approximately 2.5% and repeatability was 1.4% (coefficient of variation) in the determination of BSIP. Six operators took repeat measures on human lower legs; coefficients of variation were typically around 5%, and 3% for the more skilled operators. Location of the center of mass of the lower leg was found to move up 1.7 cm proximally when the triceps surae muscles went from a relaxed state to causing plantar flexion. The force during an impact associated with such motion of the soft tissue of the lower leg was estimated to be up to 300 N. In summary, a new repeatable and accurate method for determining BSIP has been developed, and has been used to evaluate body segment mass redistribution due to muscular contraction.

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Robert D. Catena, Nigel Campbell, Alexa L. Werner, and Kendall M. Iverson

relative body mass and dynamic balance changes during pregnancy. 19 However, this previous study did not employ a longitudinal test design, so it remains unclear if mass change affects dynamic balance changes during pregnancy. Also unknown is how much mass distribution changes throughout the body, rather