# Development of a Simplified Human Body Model for Movement Simulations
## 1 Introduction  
The development and application of human body models are inextricably connected to the analysis of human movements. This is important in many fields, including medicine, sport, and robotics. Biomechanics, as a field of science, is constantly developing due to the desire to learn the principles governing both the movement of the human body and the application of various measurement equipment and techniques. Gait is often measured with accurate, but rather expensive, and requiring large space, sets of cameras in commercial systems like Vicon [1, 2], Contemplas [3], OptotrakCertus [4], and often with markers placed on the human body [5]. Human movement can also be measured with extensible wires that may be fastened to various body parts [6], as well as with the use of wearable sensors like IMUs (an inertial measurement unit) [7] for testing gait on a treadmill [8] or for knee joint characterization [9]. Other more specific movements are also measured, i.e., a backward tucked somersault [10] or human gait with Nordic walking poles [11], which frequently apply a particularly developed measurement system. Data from measurements are often used in models for motion simulation, visualization, analyzing movement, and finding further kinematic and dynamic parameters. For example, the research in [12] presents a reproduction of human gait with the use of Nordic walkingpoles using a model built in the Adams system (multibody simulation software). Data based on measurements from the Optotrak system were used. Again in the [PERSON] program, data obtained with electrogoniometers were applied to simulate a model of human body gait with an exoskeleton [13]. Very precise and complicated human body models often involve particular body parts or joints, like the human knee joint model presented in [14], which was built based on computed tomography, magnetic resonance, and 3D-video-fluoroscopy. In another instance [15], to model the static and dynamic states of loading for bones in the skeletal system, medical images from PET scans and computer tomography were used. However, in the case of modeling the whole human body motion system, many concepts have been created, including models by [PERSON] [16], [PERSON] [17], and [PERSON] [18], as well as a model built in the so-called AnyBody system [19]. The [PERSON] model is parameterized based on anthropometric data describing the dimensions of the human body (a minimum of 25 measurements are required to build the model). The model assumes symmetry of the body segments and consists of 15 rigid solids with simple geometric shapes. Each segment has a uniform density and is characterized by the position of the center of mass (COM) and moments of inertia with regard to the three main axes of rotation. The limbs are connected to the trunk using spherical joints with zero mass [16]. The [PERSON] model consists of 17 segments. It is similar to the [PERSON] model, but has the right and left shoulder elements added. Each segment is divided into many plates--smaller rigid solids with their own density and complex shapes (e.g., parabolic plates and hollowed cylindrical sections). The model assumes no body symmetry and takes into consideration gender and individual factors such as pregnancy or being overweight. Therefore, as many as 242 individual measurements are required, including 160 diameters and the circumference of the ellipses used to model limbs. It is considered one of the most complicated and accurate human body models [17]. The Yeadon model assumes symmetry and consists of 11 segments divided into 40 rigid solids, each with a uniform density. The segments' shapes are not very complex, but 95 body measurements are required to create the model. Each joint has at least one rotation; however, for the neck, ankle, and wrist joints, no movements are considered [18; 20]. The last mentioned model (Anybody) is different from previous models.