Anthropometric Scaling Research Articles

Advanced subject-specific neck musculoskeletal modeling unveils sex differences in muscle moment arm and cervical spine loading

Neck pain and injuries are growing healthcare burdens with women having a higher incidence rate and poorer treatment outcomes than males. A better understanding of sex differences in neck biomechanics, foundational for more targeted, effective prevention or treatment strategies, calls for more advanced subject-specific musculoskeletal modeling. Current neck musculoskeletal models are based on generic anatomy, lack subject specificity beyond anthropometric scaling, and are unable to accurately reproduce neck strengths exhibited in vivo without arbitrary muscle force scaling factors or residual torque actuators. In this work, subject-specific neck musculoskeletal models of 23 individuals (11 male, 12 female) were constructed by integrating multi-modality imaging and biomechanical measurements. Each model simulated maximal voluntary neck static exertions in three postures: neck flexion in a neutral posture, flexion in a 40° extended posture, and extension in a 40° flexed posture. Quantitative model validation showed close agreement between model-predicted muscle activation and EMG measurement. The models unveiled that (1) males have greater moment arms in one flexor muscle group and five extensor muscle groups, (2) females exhibited higher cervical spinal compression per unit exertion force in the flexed posture, and (3) the variability of compression force was much greater in females in all three exertions but most notably in the extension with a flexed “dropped head” position. These insights illuminated a plausible pathway from sex differences in neck biomechanics to sex disparities in the risk and prevalence of neck pain.

Measuring fascicle lengths of extrinsic and intrinsic thumb muscles using extended field-of-view ultrasound

Complex motion of the human thumb is enabled by the balanced architectural design of the extrinsic and intrinsic thumb muscles. Given that recent imaging advances have not yet been applied to enhance our understanding of the in vivo properties of thumb muscles, the objective of this study was to test the reliability and validity of measuring thumb muscle fascicle lengths using extended field of view ultrasound (EFOV-US). Three muscles (FPL: flexor pollicis longus, APB: abductor pollicis brevis, and ECU: extensor carpi ulnaris) were imaged in eight healthy adults (4 female; age, 21.6 ± 1.3 years; height, 175.9 ± 8.3 cm)[mean ± SD]. Measured fascicle lengths were compared to cadaveric data (all muscles) and ultrasound data (ECU only). Additionally, to evaluate how fascicle lengths scale with anthropometric measurements, height, forearm length, hand length, and hand width were recorded. The EFOV-US method obtained precise fascicle length measurements [mean ± SD] for the FPL (6.2 ± 0.5 cm), APB (5.1 ± 0.3 cm), and ECU (4.0 ± 0.4 cm). However, our EFOV-US measurements were consistently different (p < 0.05) than prior cadaveric data, highlighting the need to better understand differences between in vivo and ex vivo fascicle length measurements. Fascicle length was significantly related to only hand length (r2 = 0.56, p = 0.03) for APB, highlighting that anthropometric scaling may not accurately estimate thumb muscle length. As the first study to apply EFOV-US to measure thumb muscle fascicle lengths, this study expands the utility of this imaging technology within the upper limb.

From pregnancy to breastfeeding: adequate maternal body mass index is essential to prevent a high body mass index in your children.

To verify the associations between prenatal and perinatal factors with offspring body mass index (BMI) and the moderator role of maternal BMI in this relationship. Cross-sectional study developed with 1,562 children and adolescents aged between 6 and 17years, as well as their mothers, from southern Brazil. The prenatal and perinatal factors, weight, and height for the calculation of maternal BMI were self-reported. For the calculation of BMI, weight and height of the child/adolescent were measured on an anthropometric scale with a coupled stadiometer. Linear regression models were used for the moderation analysis. All analyzes were adjusted for the mother's and child's age, sex, sexual maturation, skin color/race, and educational level. cesarean as type of delivery (β=0.66; 95% CI=0.22 1.04; p=0.002) and pregnancy complications (β=0.60; 95% CI=0.15 1.04; p=0.002) were positively associated with offspring BMI. Schoolchildren who were breastfed for 4-6months showed-0.56kg/m2 of BMI (95% CI=-1.06-0.06; p=0.02). Birth weight was also associated with BMI, with low weight being inversely (β=-0.59; 95% CI=-1.03-0.15; p=0.008), while overweight was positively related (β=0.84; 95% CI=0.08 1.60; p=0.02). The moderation analysis indicated a positive interaction between the mother's BMI and cesarean, pregnancy complications, and smoking with the offspring's BMI. On the other hand, there was an inverse association between breastfeeding from 7 to 12months and the offspring BMI, only in mothers with high BMI. Adequate maternal BMI is essential to prevent a high BMI in their children, especially when considering the influence of prenatal and perinatal risk factors.

Evaluating anthropometric scaling of a generic adult model to represent pediatric shoulder strength

The structure of the developing musculoskeletal system during childhood and adolescence influences tissue loading and function. Anatomical features important for musculoskeletal loading such as muscle volume and limb proportion vary with age but limited available anatomical data for the developing limb makes predicting loads challenging. Our aim was to evaluate whether anthropometric scaling of an existing adult musculoskeletal upper limb model is sufficient to accurately represent pediatric strength. An adult upper limb model was scaled using two scale factors based on length features and max isometric force (MIF). Length features (e.g. limb and muscle length) were scaled based on linear regression for available literature reports of forearm length vs. height (N = 366 Pediatric, N = 107 Adults), while MIF was scaled based on relating body mass vs. total shoulder muscle volume (N = 6). Children-specific models were developed for 6 pediatric individuals whose height, body mass, and shoulder moment-generating capacity (a common measure of strength) were previously reported. These models were used to predict isometric shoulder moments for flexion/extension, internal/external rotation, and ad/abduction and compared with physical measurements previously reported. The predicted isometric shoulder moments were significantly correlated to measured moments for these same individuals (p < 0.04, r2 > 0.7). However, predicted moments tended to underestimate measured values; shoulder external rotation was most accurately predicted (slope: 1.1234) while shoulder adduction was most underestimated (slope: 0.4624). This work provides an initial basis for pediatric scaling but illustrates the important need for additional direct measures of muscle size and limb strength and function in a pediatric population.

Inclusion of image-based in vivo experimental data into the Hill-type muscle model affects the estimation of individual force-sharing strategies during walking

The study of muscle coordination requires knowledge of the force produced by individual muscles, which can be estimated using Hill-type models. Predicted forces from Hill-type models are sensitive to the muscle’s maximal force-generating capacity (Fmax), however, to our knowledge, no study has investigated the effect of different Fmax personalization methods on predicted muscle forces. The aim of this study was to determine the influence of two personalization methods on predicted force-sharing strategies between the human gastrocnemii during walking. Twelve participants performed a walking protocol where we estimated muscle activation using surface electromyography and fascicle length, velocity, and pennation angle using B-mode ultrasound to inform the Hill-type model. Fmax was determined using either a scaling method or experimental method. The scaling method used anthropometric scaling to determine both muscle volume and fiber length, which were used to estimate the Fmax of the gastrocnemius medialis and lateralis. The experimental method used muscle volume and fascicle length obtained from magnetic resonance imaging and diffusion tensor imaging, respectively. We found that the scaling and the experimental method predicted similar gastrocnemii force-sharing strategies at the group level (mean over the participants). However, substantial differences between methods in predicted force-sharing strategies was apparent for some participants revealing the limited ability of the scaling method to predict force-sharing strategies at the level of individual participants. Further personalization of muscle models using in vivo experimental data from imaging techniques is therefore likely important when using force predictions to inform the diagnosis and management of neurological and orthopedic conditions.

Association between food consumption and high levels of low density lipoprotein cholesterol among obese children.

The increase in the prevalence of obesity and obesity in children is a pattern of the last decades. This public health issue results in metabolic disorders such as dyslipidemia with increased LDL-C. Previous findings shows that most of the Brazilian children does not follow the recommended consumption of fruits and vegetables. To evaluate the association of dietary intake characteristics with elevated serum cholesterol from low density lipoprotein in obese children. Cross-sectional study involving 137 obese children (5-10 years). The mean age of the studied children was 8.27 years, 55.5% were male The weight measurements were performed on a digital anthropometric scale. The body mass index was calculated for each child and the Food Frequency Questionnaire was applied. The peripheral blood was collected for lipid profile analysis. Stata 12.0 statistical package was used to analyze the data, considering a significance level of p < 0.05. The prevalence of hypercholesterolemia based on the serum cholesterol from low density lipoprotein fraction was 14.6%. It was observed that children in the group who consumed the lower difference of risky and protective foods on a daily basis were not less likely to have a high cholesterol from low density lipoprotein level as a criterion for hypercholesterolemia (p = 0.218). A large proportion of the individuals presented levels of lipid profile classified as undesirable for age, as well as food rich in components capable of increasing this profile, which should encourage the intensification in measures of prevention of cardiovascular diseases since childhood.

Anthropometric scaling of musculoskeletal models of the hand captures age-dependent differences in lateral pinch force

Musculoskeletal models and computer simulations enable non-invasive study of muscle function and contact forces. Hand models are useful for understanding the complexities of hand strength, precision movement, and the dexterity required during daily activities. Yet, generic models fail to accurately represent the entire scope of the population, while subject-specific models are labor-intensive to create. The objective of this study was to assess the efficacy of scaled generic models to represent the broad spectrum of strength profiles across the lifespan. We examined one hundred lateral pinch simulations using a generic model of the wrist and thumb anthropometrically scaled to represent the full range of heights reported for four ages across childhood, puberty, older adolescence, and adulthood. We evaluated maximum lateral pinch force produced, muscle control strategies, and the effect of linearly scaling the maximum isometric force. Our simulations demonstrated three main concepts. First, anthropometric scaling could capture age-dependent differences in pinch strength. Second, a generic muscle control strategy is not representative of all populations. Lastly, simulations do not employ optimal fiber length to complete a lateral pinch task. These results demonstrate the potential of anthropometrically-scaled models to study hand strength across the lifespan, while also highlighting that muscle control strategies may adapt as we age. The results also provide insight to the force–length relationship of thumb muscles during lateral pinch. We conclude that anthropometric scaling can accurately represent age characteristics of the population, but subject-specific models are still necessary to represent individuals.

Lean body mass is the strongest anthropometric predictor of left ventricular mass in the obese paediatric population.

Indexing left ventricular mass to body surface area or height2.7 leads to inaccuracies in diagnosing left ventricular hypertrophy in obese children. Lean body mass predictive equations provide the opportunity to determine the utility of lean body mass in indexing left ventricular mass. Our objectives were to compare the diagnostic accuracy of predicted lean body mass, body surface area, and height in detecting abnormal left ventricle mass in obese children. Obese non-hypertensive patients aged 4-21 years were recruited prospectively. Dual-energy X-ray absorptiometry was used to measure lean body mass. Height, weight, sex, race, and body mass index z-score were used to calculate predicted lean body mass. We enrolled 328 patients. Average age was 12.6 ± 3.8 years. Measured lean body mass had the strongest relationship with left ventricular mass (R2 = 0.84, p < 0.01) compared to predicted lean body mass (R2 = 0.82, p < 0.01), body surface area (R2 = 0.80, p < 0.01), and height2.7 (R2 = 0.65, p < 0.01). Of the clinically derived variables, predicted lean body mass was the only measure to have an independent association with left ventricular mass (β = 0.90, p < 0.01). Predicted lean body mass was the most accurate scaling variable in detecting left ventricular hypertrophy (positive predictive value = 88%, negative predictive value = 99%). Lean body mass is the strongest predictor of left ventricular mass in obese children. Predicted lean body mass is the most accurate anthropometric scaling variable for left ventricular mass in left ventricular hypertrophy detection. Predicted lean body mass should be considered for clinical use as the body size correcting variable for left ventricular mass in obese children.

Neck musculoskeletal model generation through anthropometric scaling

A new methodology was developed to quickly generate whole body models with detailed neck musculoskeletal architecture that are properly scaled in terms of anthropometry and muscle strength. This method was implemented in an anthropometric model generation software that allows users to interactively generate any new male or female musculoskeletal models with adjustment of anthropometric parameters (such as height, weight, neck circumference, and neck length) without the need of subject-specific motion capture or medical images. 50th percentile male and female models were developed based on the 2012 US Army Anthropometric Survey (ANSUR II) database and optimized with a novel bilevel optimization method to have strengths comparable to experimentally measured values in the literature. Other percentile models (ranging from the 1st to 99th percentile) were generated based on anthropometric scaling of the 50th percentile models and compared. The resultant models are reasonably accurate in terms of both musculoskeletal geometry and neck strength, demonstrating the effectiveness of the developed methodology for interactive neck model generation with anthropometric scaling.

Agreement Between Measured BMI and Reported BMI Obesity Definitions in a Brazilian Civil Servants

Body mass index (BMI) is a worldwide used method for obesity identification. It is an easy and low-cost method recommended for large samples assessment. Concerns exit regarding the risk of misclassification when BMI is calculated based on reported height and weight as compared to the measured height and weight for BMI calculation. PURPOSE: We compared the prevalence of obesity categorized by measured BMI (m-BMI) and reported BMI (r-BMI) among Brazilian civil servant. METHODS: We evaluated 398 randomly selected volunteers (42.2% men), aged 44.8±8.7 yrs, m-BMI: 25.6±4.7 kg/m2, from a federal labor court. Volunteers reported weight and height in a health questionnaire without knowing that they would be subsequently measured in an anthropometric scale (Welmy-RI W200). Both m-BMI and r-BMI were calculated using the Quetelet formula: BMI = (weight in kg)/(height in m2). Obesity was defined as BMI ≥30.0 kg/m2. Due to lower sensitivity among women, a BMI ≥29.0 kg/m2 alternative cut-off point was also tested. Agreement analyses was done considering m-BMI as reference, using following indices: 1) total agreement (TA) as the sum of the percentage of true positive and true negative values (TA=TP+TN); 2) sensitivity = [TP / (TP+FN)] X 100, were FN is false negative; 3) specificity = [TN /(TN+FP)] X 100. All indices were calculated as their point value and 95% interval of confidence (95%IC). RESULTS: Agreement indices are shown on Figure 1. When the 29.0 kg/m2 cut-off point was used in the r-BMI, we found a much higher sensitivity (88.2%) with small reductions on TA (-1.4%) and specificity (-3.1%). CONCLUSION: We observed very high agreement between r-BMI as compared to m-BMI in the total sample and among men. The accuracy of r-BMI to identify obesity among women was lower than among men, probably affected by its lower prevalence. Using the 29.0 kg/m2 alternative cut-off point for women resulted on a sensitivity as good as in men. r-BMI also showed to be a highly specific method to exclude obesity.Figure 1: Agreement between measurement BMI (kg/m2) and reported BMI in Brazil civil servant (n=398)

Resting Energy Expenditure Measured by Indirect Calorimetry in Obese Patients: Variation Within Different BMI Ranges.

The adequate provision of energy for obese patients by estimation without indirect calorimetry (IC) is challenging. The goal was to establish values of kilocalories per kilogram (kcal/kg) for patients in different ranges of body mass index (BMI [kg/m2 ]) comparable to resting energy expenditure (REE [kcal/kg/d]) measurements by IC. In 63 overweight (OW) hospitalized patients with BMIs (25.0-29.9) or obesity (OB; ≥30), the REE was measured in fasting and fed states. IC was performed with Deltatrac II on patients with enteral or parenteral nutrition, classified by their BMI, in 3 groups: OW (25-29.9), OB (30-39.9), and morbidly obese (≥40). The actual body weight was measured with a microprocessed bed scale or a precision anthropometric scale, and REE was transformed to kcal/kg. Ninety-seven IC measurements were obtained from 63 patients: in 54 on a ventilator, and of 9 with a canopy; 58 in the fasting state; and 39 after reaching measured caloric requirements. The patients' BMIs ranged from 27.3 to 53.4, average of 33.9 ± 6.2. There were no differences in measured REE (mREE) between the fasting and fed states (P > 0.05) within each BMI group; however, differences were observed when comparing the mREE between the groups in the fed state. These results, in kcal/kg/d, suggest using 22.0 for OW, 18.4 for OB, and 16.9 for individuals with BMIs >40. However, we recommend the use of IC to determine REE for the latter subset of patients, since 16.9kcal/kg/d might be an underestimation.

Anthropometric Scaling of Anatomical Datasets for Subject-Specific Musculoskeletal Modelling of the Shoulder

Linear scaling of generic shoulder models leads to substantial errors in model predictions. Customisation of shoulder modelling through magnetic resonance imaging (MRI) improves modelling outcomes, but model development is time and technology intensive. This study aims to validate 10 MRI-based shoulder models, identify the best combinations of anthropometric parameters for model scaling, and quantify the improvement in model predictions of glenohumeral loading through anthropometric scaling from this anatomical atlas. The shoulder anatomy was modelled using a validated musculoskeletal model (UKNSM). Ten subject-specific models were developed through manual digitisation of model parameters from high-resolution MRI. Kinematic data of 16 functional daily activities were collected using a 10-camera optical motion capture system. Subject-specific model predictions were validated with measured muscle activations. The MRI-based shoulder models show good agreement with measured muscle activations. A tenfold cross-validation using the validated personalised shoulder models demonstrates that linear scaling of anthropometric datasets with the most similar ratio of body height to shoulder width and from the same gender (p < 0.04) yields best modelling outcomes in glenohumeral loading. The improvement in model reliability is significant (p < 0.02) when compared to the linearly scaled-generic UKNSM. This study may facilitate the clinical application of musculoskeletal shoulder modelling to aid surgical decision-making.

Transhumeral loading during advanced upper extremity activities of daily living.

Percutaneous osseointegrated (OI) implants for direct skeletal attachment of upper extremity prosthetics represent an alternative to traditional socket suspension that may yield improved patient function and satisfaction. This is especially true in high-level, transhumeral amputees where prosthetic fitting is challenging and abandonment rates remain high. However, maintaining mechanical integrity of the bone-implant interface is crucial for safe clinical introduction of this technology. The collection of population data on the transhumeral loading environment will aid in the design of compliance and overload protection devices that mitigate the risk of periprosthetic fracture. We collected marker-based upper extremity kinematic data from non-amputee volunteers during advanced activities of daily living (AADLs) that applied dynamic loading to the humerus. Inverse dynamic analysis was applied to calculate the axial force, bending and torsional moments at three virtual amputation levels representing 25, 50, and 75% residual humeral length. The influences of amputation level, elbow flexion constraint, gender and anthropometric scaling were assessed. Results indicate that the proximal (25%) amputation level experienced significantly higher axial forces and bending moments across all subjects when compared to distal amputation levels (p≤0.030). Constraining elbow flexion had a limited influence on peak transhumeral loads. Male subjects experienced higher axial forces during all evaluated activities (p≤0.023). Peak axial force for all activities occurred during jumping jacks (174.5N). Peak bending (57.6Nm) and torsional (57.2Nm) moments occurred during jumping jacks and rapid internal humeral rotation, respectively. Calculated loads fall within the range of implant fixation failure loads reported in cadaveric investigations of humeral stem fixation; indicating that periprosthetic fracture may occur during non-contact AADLs. These kinematic data, collected over a range of AADLs, will aid in the development of overload protection devices and appropriate post-operative rehabilitation protocols that balance return to an active lifestyle with patient safety.

Analyzing Level of Service Through Anthropometric Scale and Its Contribution to Transportation Engineering

In this study, the usage of the level of service (LOS) concept, which was developed specifically for pedestrian satisfaction and safety, was critically analyzed. The focuses of this investigation were the Fruin and Highway Capacity Manual (HCM) LOS values, which were evaluated and compared in terms of their anthropometric dimensions. In this paper, new LOS values are proposed on the basis of the critical evaluation of the HCM and Fruin LOS values revealing the inconsistencies between the LOS values and the analysis. The importance of emptiness area in calculating human comfort and satisfaction in terms of the anthropometric dimensions and LOS value is also discussed. A software program called Laborer Image Analysis Software (LIAS) was developed to evaluate and compare the impacts of different body dimensions on the LOS values and on the space requirements for pedestrians. LIAS is presented as a facilitation tool for calculating more concise and effective emptiness areas and LOS values. The comfort area concept is also presented and discussed. This discussion is used to reveal the contrasts and inconsistencies in the existing usage of the LOS concept and to highlight the importance of the emptiness area approach. The paper presents a different perspective and discussion on the existing utilization of LOS levels, particularly for pedestrians in different structures. The research contributes to the LOS analysis discussion in terms of the anthropometric scale according to changing user profiles and develops facilitator(s) for analyzing and applying amendments to pedestrian needs, which can be used in transportation buildings.

Abstract 10882: Scaling to Lean Body Mass Accurately Classifies Abnormal LV Mass in Obese Children

Introduction: Scaling LV mass to BSA or height leads to inaccuracies in the diagnosis of LV hypertrophy in the obese pediatric population. Lean body mass (LBM) is free of the scaling biases seen with BSA and height. Our objectives were to 1) validate predictive equations for LBM, 2) determine the ideal scaling variable for LV mass, and 3) compare the diagnostic accuracy of predicted LBM (LBMp), BSA, and height in detecting abnormal LV mass in obese children. Methods: Obese subjects ages 4 to 21 were recruited prospectively. Height, weight, sex, race and body mass index z-score were used to calculate LBMp. LV mass was measured by echocardiography. Dual-energy X-ray absorptiometry was used to measure LBM (LBMm). Bland-Altman plots were used to assess agreement between LBMp and LBMm. Linear regression was performed to assess the ideal scaling variable for LV mass. Centile curves of LV mass vs. LBMm as the reference-standard were compared with curves derived from LBMp, BSA, and height 2.7 to assess their accuracy in detecting elevated LV mass. Results: 309 subjects were enrolled for predictive equation validation, 195 had echocardiography performed. Mean age was 11.8 ± 3.4 years. The mean difference between LBMp and LBMm was 1.5% (95% limits of agreement: -16.5%, 19.4%). LBMm had the strongest relationship with LV mass (R 2 = 0.83, p &lt; 0.01) compared to LBMp (R 2 = 0.81, p &lt; 0.01), BSA (R 2 = 0.77, p &lt; 0.01), and height 2.7 (R 2 = 0.67, p &lt; 0.01). Of the clinically derived variables, LBMp was the only measure to retain a relationship with LV mass upon multivariable regression (partial r = 0.89). LBMp was the most accurate scaling variable in detecting LV hypertrophy (PPV = 85.7%, NPV = 99.3%) compared to BSA and height 2.7 . Conclusions: LBM predictive equations are accurate in obese children. LBM is the strongest predictor of LV mass in obese children. LBMp is the most accurate anthropometric scaling variable for LV mass in LV hypertrophy detection. LBMp should be considered for widespread clinical use as the body size correcting variable for LV mass in obese children.

Development of a kinematic model to predict finger flexor tendon and subsynovial connective tissue displacement in the carpal tunnel

Finger flexor tendinopathies and carpal tunnel syndrome are histologically characterised by non-inflammatory fibrosis of the subsynovial connective tissue (SSCT) in the carpal tunnel, which is indicative of excessive and repetitive shear forces between the finger flexor tendons and SSCT. We assessed flexor digitorum superficialis (FDS) tendon and adjacent SSCT displacements with colour Doppler ultrasound as 16 healthy participants completed long finger flexion/extension movements captured by a motion capture system. FDS tendon displacements fit a second-order regression model based on metacarpophalangeal and proximal interphalangeal joint flexion angles (R2 = 0.92 ± 0.01). SSCT displacements were 33.6 ± 1.7% smaller than FDS tendon displacements and also fit a second-order regression model (R2 = 0.89 ± 0.01). FDS tendon and SSCT displacement both correlated with finger joint thickness, enabling participant-specific anthropometric scaling. We propose the current regression models as an ergonomic method to determine relative displacements between the finger flexor tendons and SSCT.

The Effects of Anthropometric Scaling Parameters on Normalized Muscle Strength in Uninjured Baseball Pitchers

Muscle force must be normalized for between-subjects comparisons of strength to be valid. The most effective method for normalizing muscle strength has not, however, been systematically evaluated. To evaluate the effects of normalizing muscle strength using a spectrum of anthropometric parameters. Cross-sectional. Laboratory. 50 uninjured high-school-age baseball pitchers. Shoulder-rotation strength was tested at 0° and 90° abduction with a handheld dynamometer. Muscle force was normalized to parameters including subject height, weight, height × weight, body-mass index (BMI), forearm length, and forearm length × height. Statistical analysis included evaluating the coefficient of variation, skewness, and kurtosis of the nonnormalized and normalized muscle force. The most effective normalization method was determined based on the scaling factor that yielded the lowest variability for the data set and promoted the most normal distribution of the data set. Using body weight to scale muscle force was the most effective anthropometric parameter for normalizing strength values based on the group of statistical measures of variability. BMI, height × weight, and forearm length × weight as scaling factors also yielded less variable values for muscle strength compared with nonnormalized strength, but less consistently than body weight. Height and forearm length were least effective in reducing the variability of the data set relative to nonnormalized muscle force. This study provides objective support for scaling muscle strength to subject body weight. This approach to normalizing muscle strength uses methods readily accessible to clinicians and researchers and may facilitate the identification of differences in strength between individuals with diverse physical characteristics.

Modelling tendon excursions and moment arms of the finger flexors: Anatomic fidelity versus function

A detailed musculoskeletal model of the human hand is needed to investigate the pathomechanics of tendon disorders and carpal tunnel syndrome. The purpose of this study was to develop a biomechanical model with realistic flexor tendon excursions and moment arms. An existing upper extremity model served as a starting point, which included programmed movement of the index finger. Movement capabilities were added for the other fingers. Metacarpophalangeal articulations were modelled as universal joints to simulate flexion/extension and abduction/adduction while interphalangeal articulations used hinges to represent flexion. Flexor tendon paths were modelled using two approaches. The first method constrained tendons with control points, representing annular pulleys. The second technique used wrap objects at the joints as tendon constraints. Both control point and joint wrap models were iteratively adjusted to coincide with tendon excursions and moment arms from a anthropometric regression model using inputs for a 50th percentile male. Tendon excursions from the joint wrap method best matched the regression model even though anatomic features of the tendon paths were not preserved (absolute differences: mean<0.33 mm, peak<0.74 mm). The joint wrap model also produced similar moment arms to the regression (absolute differences: mean<0.63 mm, peak<1.58 mm). When a scaling algorithm was used to test anthropometrics, the scaled joint wrap models better matched the regression than the scaled control point models. Detailed patient-specific anatomical data will improve model outcomes for clinical use; however, population studies may benefit from simplified geometry, especially with anthropometric scaling.

Effects of Anthropometric Scaling on Rotator Cuff Muscle Strength

Effects of Anthropometric Scaling on Rotator Cuff Muscle Strength

Using two palpable measurements improves the subject-specific femoral modeling

Subject-specific musculoskeletal models are essential to biomedical research and clinical applications, such as customized joint replacement, computer-aided surgical planning, gait analysis and automated segmentation. Generating these models from CT or magnetic resonance imaging (MRI) is time and resource intensive, requiring special skills. Therefore, in many studies individual bone models are approximated by scaling a generic template. Thus, the primary goal of this study was to determine a set of clinically available parameters (palpable measures and demographic data) that could improve the prediction of femoral dimensions, as compared to predicting these variables using uniform scaling based on palpable length. Similar to previous non-homogenous anthropometric scaling methods, the non-homogenous scaling method proposed in this study improved the prediction over uniform scaling of five key femoral measures. Homogenous scaling forces all dimensions of an object to be scaled equally, whereas non-homogenous scaling allows the dimensions to be scaled independently. The largest improvement was in femoral depth, where the coefficient of determination ( r 2) improved from 0.22 (homogenous) to 0.60 (non-homogeneous). In general, the major advantage of this non-homogenous scaling method is its ability to support the accurate and rapid generation of subject-specific femoral models since all parameters can be collected clinically, without imaging or invasive methods.