# Development of a Simplified Human Body Model for Movement Simulations
## 2 Materials and Methods  
### The Developed Human Body Model  
A simplified human body model for movement simulations is described in this article. The development of the model initially required the interpretation and simplification of the human body in terms of kinematics and dynamics. Above all, this involves the number of segments and the number and type of connections (joints). The model's main assumptions are that it should be parametric, simple to use (a small number of necessary measurements), and as universal as possible, even at the cost of reduced individualization. In the model, 17 rigid solids are distinguished (Figure 1a), as proposed in the Hanavan model. The Hanavan model was chosen as the basis due to its established use in biomechanics research and its relatively comprehensive representation of human anatomy. Furthermore, it exhibits a level of complexity that aligns well with the desired level of detail for the intended simplified approach. The difference lies in the addition of the pelvis and neck (parts 8 and 9). Moreover, the two parts of the torso (indicated as 3 and 4) are initially separated so that the appropriate shapes and dimensions of these parts can be determined. However, they are connected to one solid (they do not move relative to each other, ultimately forming a rigid element). The model, therefore, contains 16 segments that are connected to each other in a movable way. Human body joints are treated as spherical joints--class III kinematic pairs (p\({}_{3}\) = 13), and they follow common biomechanical interpretations. Only elbow joints are treated as class II kinematic pairs (universal/cardan joints p\({}_{2}\) = 2). Consequently, in the elbows,--2 possible rotational movements are taken into consideration--flexion/extension (F/E) and internal/external rotation (Rot), while in all the other joints--also abduction/adduction (A/A). For the purpose of the model's analysis and interpretation of its mobility, the pelvis was considered to be connected with a spherical joint to the ground (immobile part). This means that the model's mobility is equal to W\({}_{\text{R}}\) = 6 \(\times\) (17 - 1) - 5 \(\times\) 0 - 4 \(\times\) 2 - 3 \(\times\) 14 - 2 \(\times\) 0 - 1 \(\times\) 0 = 46, and therefore, in order to unambiguously determine the position of each member of the model, it is necessary to assign 46 angular parameters to it (apply 46 drives). Particular emphasis is placed on the precise definitions of the shapes and dimensions of each designed segment of the body model (Figure 1b). Moreover, the dimensions are parameterized and dependent on only one value (body height). The segment shapes and equations of dimensions are listed in Table 11 (Appendix A). Generally, the modeled dimensions and masses are based on [22], whereas the shapes follow the suggestions of the Hanavan model [16]. The shapes of the body segments were assumed to be simple rigid solids, as follows: feet--a triangular prism, hands, and head--an ellipsoid, the remaining segments of the upper and lower limbs and the thorax and abdomen--a truncated cone, neck--a cylinder, pelvis--a double pyramid with a square base. Several dimensions that are missing in the above sources (e.g., neck or head radius) have been added based on the dimensions for a man in the 50 th percentile--according to the Atlas of Human Measurements [23]. More precisely, the data used concerned an individual of Caucasian race, aged 20-60. Based on the values from this source, the missing dimension equations were also determined and were dependent only on the total human height (Table A1). As for the dynamic aspects of the model, the masses of individual segments are mainly determined based on paper [22] and are presented in Table A2 (Appendix A) in parametric equations, which are dependent on only one value (body mass). At this stage of the research work, the COM location for individual segments is not referred to in the literature data (for simplification purposes).