# Experimental Study of Military Crawl as a Special Type of Human Quadripedal Automatic Locomotion
## 2 Materials and Methods
### Equipment  
The kinematics were recorded by the Optitrack optical system (\"Motion Capture Systems\". OptiTrack, [[http://www.optitrack.com/index.html](http://www.optitrack.com/index.html)]([http://www.optitrack.com/index.html](http://www.optitrack.com/index.html)), accessed on 3 May 2021) which consists of 12 Flex 13 cameras, 100 Hz each. The cameras are placed at a height of 2.2 m evenly around the perimeter of the room, which was 5 \(\times\) 8 m. The examination was arranged based on the standard procedure: calibration and marker fixation. For the participants there was a set of 13 light-reflecting markers fixed on the following joints (1 marker on each joint): shoulder, elbow, radiocarbon, knee and ankle joints. The remaining 3 markers were fixed on the subject's back: 2 markers on the left and on the right at the level of the sacroiliac joints and 1 on the 10 th spinous process of verteb (Figure 2).  
Two particular markers are connected with a straight line thus forming the links of the model. The links form joints. Thereby the angle in the joint is determined by three markers (Figure 2).  
The crawling cycle is considered to be from the moment the leg is bent in the knee and hip joints until the next knee and hip flexion of the same leg (Figure 3).  
Since the model is somewhat simplified, the obtained coniograms only partly reflect the joint movements. These movements are studied only in the projection of a horizontal surface. However, to make the description less complicated, we will keep calling them hip, knee, shoulder and elbow joints.  
Figure 3: Sequential phases of a full cycle of motions for the right side—upper row and left side—lower row.  
Figure 2: Points where markers were fixed: acrom, lateral elbow epicondyle, external place of wrist (watches wrist placement), spina iliac posterior superior, trochanter major, lateral epicondyle of the knee, lateral malleolus.  
After the records made with the Optitrack system have been processed in the standard way, further processing was performed based on Visual 3D (C-Motion Inc., USA). For the biomechanical analysis of the military crawl task, there has been a special simplified multilink model of a human body developed, which consists of eight links which form eight joints in the horizontal plane.  
The beginning and end of each motion cycle on each side (right and left) are determined manually based on the data about the shift of the markers fixed on the lateral malleolus. After that a report containing one-cycle kinematics parameters was generated.  
The report includes the following standard biomechanics information: a movement pattern of the marker fixed at the level of the 10 th spinous process of vertebra, cycle duration, proportion between the beginning of one cycle and beginning of the next cycle (in percentage), diagrams of angle variance within a movement cycle (meters per second), space-time parameters: movement cycle duration (CD) in seconds, start of a cycle on the opposite side (SOpS) versus the one on the given side in percentage of CD, length of a motion cycle (LMC, meters) and speed of the 10 th spinous marker's shift--V (meters per second).  
To describe the shoulder girdle--pelvis arrangement, a special value shoulders-pelvis was used. This value is an adjoining angle formed by the lines going through the markers placed on the acromial extremities of the clavicles and markers on the pelvis.  
The data set includes the following parameters: range of motion--an amplitude for each joint from minimum to maximum and extremum phase (maximal flexion of a joint)--Tmax% (percent of CD).  
Statistical processing was performed based on Statistica 10 with the use of variation statistics methods and variance analysis. Evaluation was conducted according to Wilcoxon-Mann-Whitney criteria. These criteria was used because the distribution of parameters in the study was not parametric. This is partly due to the genesis of the values themselves, and partly to the sample size (8 participants).