Ali Asadi Nikooyan

The relationship between lower-extremity stress fractures and the ground reaction force: A systematic review

BACKGROUND lower-limb stress fracture is one of the most common types of running injuries. There have been several studies focusing on the association between stress fractures and biomechanical factors. In the current study, the ground reaction force and loading rate are examined. There is disagreement in the literature about whether the history of stress fractures is associated with ground reaction forces (either higher or lower than control), or with loading rates. METHODS a systematic review of the literature was conducted on the relationship between the history of tibial and/or metatarsal stress fracture and the magnitude of the ground reaction force and loading rate. Fixed-effect meta-analysis techniques were applied to determine whether or not the ground reaction force and/or loading rate are different between the stress fracture and control groups. FINDINGS thirteen articles were identified through a systematic search of the literature. About 54% of these articles reported significantly different vertical ground reaction force and/or loading rate between the stress fracture and control groups. Other studies (~46%) did not observe any significant difference between the two groups. Meta-analysis results showed no significant differences between the ground reaction force of the lower-limb stress fracture and control groups (P>0.05). However, significant differences were observed for the average and instantaneous vertical loading rates (P<0.05). INTERPRETATION the currently available data does not support the hypothesis that there is a significant difference between the ground reaction force of subjects experiencing lower-limb stress fracture and control groups. Instead, the vertical loading rate was found to be significantly different between the two groups.

Mass–spring–damper modelling of the human body to study running and hopping - an overview

Several mass–spring–damper models have been developed to study the response of the human body to the collision with the ground during hopping, trotting, or running. The mass, spring, and damper elements represent the masses, stiffness properties, and damping properties of hard and soft tissues. The masses that models are composed of are connected to each other via springs and dampers. The present paper reviews the various types of mass–spring–damper models including one-body and multi-body models. The models are further categorized as being either passive or active. In passive models, the mechanical properties (stiffness and damping) of soft tissues remain constant regardless of the type of footwear, ground stiffness, etc. In active models, the mechanical properties adapt to external loads. The governing equations of motion of all models as well as their parameters are presented. The specific ways that the models take account of the shoe–ground interactions are discussed as well. The methods used for determination of different modelling parameters are briefly surveyed. The advantages and disadvantages of the different types of mass–spring–damper models are also discussed. The paper concludes with a brief discussion of possible future research trends in the area of mass–spring–damper modelling.

Effects of Muscle Fatigue on the Ground Reaction Force and Soft-Tissue Vibrations During Running: A Model Study

A modeling approach is used in this paper to study the effects of fatigue on the ground reaction force (GRF) and the vibrations of the lower extremity soft tissues. A recently developed multiple degrees-of-freedom mass-spring-damper model of the human body during running is used for this purpose. The model is capable of taking the muscle activity into account by using a nonlinear controller that tunes the mechanical properties of the soft-tissue package based on two physiological hypotheses, namely, “constant force” and “constant vibration.” In this study, muscle fatigue is implemented in the model as the gradual reduction of the ability of the controller to tune the mechanical properties of the lower body soft-tissue package. Simulations are carried out for various types of footwear in both pre- and post fatigue conditions. The simulation results show that the vibration amplitude of the lower body soft-tissue package may considerably increase (up to 20%) with muscle fatigue, while the effects of fatigue on the GRF are negligible. The results of this modeling study are in line with the experimental studies that found muscle fatigue does not significantly change the GRF peaks, but may increase the level of soft-tissue vibrations (particularly for hard shoes). A major contribution of the current study is the formulation of a hypothesis about how the central nervous system tunes the muscle properties after fatigue.

The effects of lower-extremity muscle fatigue on the vertical ground reaction force: A meta-analysis

There is currently no consensus in the literature on whether the magnitude of the ground reaction force or loading rate decreases or increases with muscle fatigue. In this article, the effects of lower extremity muscle fatigue on the magnitude of the ground reaction force and loading rate during running and drop landing are examined. Through a systematic search of the literature, 24 articles are identified that satisfy the inclusion criteria and study the relationship between fatigue and the ground reaction force variables during running, single-leg drop landing, and bilateral drop landing. The articles are categorized based on the type of locomotion they study. To determine whether or not the ground reaction force peaks/loading rate are markedly affected by fatigue, meta-analyses are conducted both separately for each type of locomotion and for an aggregate of all studies. The results of the meta-analyses show that the ground reaction force active peak significantly decreases for the following study groups: aggregate of all included studies, studies of drop landing (both single-leg and bilateral), and studies of bilateral landing only. The ground reaction force active peak did not significantly change in running and single-leg drop landing. The effects of muscle fatigue on the magnitude of the ground reaction force impact peak and loading rate was always insignificant.

Comparison of Two Methods for In Vivo Estimation of the Glenohumeral Joint Rotation Center (GH-JRC) of the Patients with Shoulder Hemiarthroplasty

Determination of an accurate glenohumeral-joint rotation center (GH-JRC) from marker data is essential for kinematic and dynamic analysis of shoulder motions. Previous studies have focused on the evaluation of the different functional methods for the estimation of the GH-JRC for healthy subjects. The goal of this paper is to compare two widely used functional methods, namely the instantaneous helical axis (IHA) and symmetrical center of rotation (SCoRE) methods, for estimating the GH-JRC in vivo for patients with implanted shoulder hemiarthroplasty. The motion data of five patients were recorded while performing three different dynamic motions (circumduction, abduction, and forward flexion). The GH-JRC was determined using the CT-images of the subjects (geometric GH-JRC) and was also estimated using the two IHA and SCoRE methods. The rotation centers determined using the IHA and SCoRE methods were on average 1.47±0.62 cm and 2.07±0.55 cm away from geometric GH-JRC, respectively. The two methods differed significantly (two-tailed p-value from paired t-Test ∼0.02, post-hoc power ∼0.30). The SCoRE method showed a significant lower (two-tailed p-value from paired t-Test ∼0.03, post-hoc power ∼0.68) repeatability error calculated between the different trials of each motion and each subject and averaged across all measured subjects (0.62±0.10 cm for IHA vs. 0.43±0.12 cm for SCoRE). It is concluded that the SCoRE appeared to be a more repeatable method whereas the IHA method resulted in a more accurate estimation of the GH-JRC for patients with endoprostheses.

A Bond Graph Approach to the Modeling of Fluid-Solid Interaction in Cardiovascuular System's Pulsatile Flow

A bond graph model of entire cardiovascular system is developed in this paper. Although relying on the concepts of previously developed lumped-parameter models, this new model benefits from some advantages of general system theory which allows the modeler to include as many details as necessary. Specifically, inclusion of pace making mechanism has become much easier. The pace making mechanism is not, however, included in this stage of model development. Modular sources of effort are, instead, predicted in the model to generate synthetic signals close to what occurs in reality. The model is simulated and results of simulation are compared with widely available data of normal cardiovascular systems pressure-flow performance. It has been shown that they are of a good agreement and the model could successfully simulate performance of the human cardiovascular system

Development of an Improved Desiccant-Based Evaporative Cooling System for Gas Turbines

The evaporative inlet cooling systems do not work well in humid areas. However, desiccant wheels can be used to dehumidify the air before passing it through the evaporative cooler. A previous study of combined direct and indirect evaporative coolers showed that a single desiccant wheel does not offer much higher effectiveness compared with the multistage evaporative systems. In this paper, additional dehumidification and indirect evaporative cooling stages are added to increase the effectiveness of the desiccant-based inlet cooling. A typical gas turbine cycle along with an industrial gas turbine with actual performance curves are used to study the performance of the proposed system in three different climatic conditions. It is shown that the added stages substantially improve the effectiveness of the desiccant-based inlet cooling.

Application of Virtual Environments to Assessment of Human Motor Learning During Reaching Movements

This paper studies learning of reaching movements in a dynamically variable virtual environment specially designed for this purpose. Learning of reaching movements in the physical world has been extensively studied by several researchers. In most of those studies, the subjects are asked to exercise reaching movements while being exposed to real force fields exerted through a robotic manipulandum. Those studies have contributed to our understanding of the mechanisms used by the human cognitive system to learn reaching movements in the physical world. The question that remains to be answered is how the learning mechanism in the physical world relates to its counterpart in the virtual world where the real force fields are replaced by virtual force fields. A limited number of studies have already addressed this question and have shown that there are, actually, quite a number of relationships between the learning mechanisms in these two different environments. In this study, we are focused on gaining a more in-depth understanding of these relationships. In our experiments, the subjects are asked to guide a virtual object to a desired target on a computer screen using a mouse. The movement of the virtual object is affected by a viscous virtual force field that is sensed by the examinees through their visual system. Three groups of examinees are used for the experiments. All the examinees are first trained in the null-field condition. Then, the viscous force field is introduced either suddenly (for the two first groups) or gradually (for the last group). While the first and third groups of the examinees used their dominant arm to guide the virtual object in the second step, the second group used their nondominant arm. Generalization of the learning from the dominant to the nondominant arm and vice versa was studied in the third phase of the experiments. Finally, the force field was removed and the examinees were asked to repeat the reaching task to study the so-called aftereffects phenomenon. The results of the experiments are compared with the studies performed in the physical world. It is shown that the trends of learning and generalization are similar to what is observed in the physical world for a sudden application of the virtual force field. However, the generalization behavior of the examinees is somewhat different from the physical world if the force field is gradually applied.

ASSESSMENT OF OSTEOPOROTIC FEMORAL FRACTURE RISK: FINITE ELEMENT METHOD AS A POTENTIAL REPLACEMENT FOR CURRENT CLINICAL TECHNIQUES

Femoral fracture risk prediction is a necessary step preceding effective pharmacological intervention or pre-operative planning. Current clinical methods for fracture risk prediction rely on 2D imaging methods and have limited predictive value. Researchers are therefore trying to find improved methods for fracture prediction. During last few decades, many studies have focused on integration of 3D imaging techniques and the finite element (FE) method to improve the accuracy of fracture assessment techniques. In this paper, we review the recent advances in FE and other techniques for predicting the risk of femoral fractures. Based on a number of selected studies, the different steps that are involved in generation of patient-specific FE models are reviewed with particular emphasis on the fracture criteria. The inaccuracies that might arise due to the imperfections of the involved steps are also discussed. It is concluded that compared to image- and geometry-based techniques, FE is a more promising approach ...

PUBLICATION AND CITATION IN BIOMECHANICS: A COMPARISON WITH CLOSELY RELATED FIELDS (2003–2010)

The publication and citation patterns of the journals published in the broad area of Biomechanical engineering are compared with those of the journals published in several other closely related areas of research. The data published in ISI Journal Citation Reports® (2003–2010) for different subject categories is used for this purpose. A subject category comprising of Biomechanics journals is defined in this article. It is shown that the aggregate impact factor of the journals included in the defined subject category has been increasing with a slower pace as compared to the aggregate impact factor of the journals belonging to all other subject categories considered in the current study. More extensive research is required to clarify the reasons for the observed patterns.