# A Review on Ergonomics in Agriculture. Part II: Mechanized Operations
## 4 Results
### Brief Review of Literature Classified into Agricultural Machinery Types
#### 4.2.1 Tractor
In [58], different tractor types and speeds having three tillage implements (namely a plough, a disk narrow and a cultivator) were examined. The tractors seem to play the primary role in the development of vibration along the lateral axis, while the implements along the horizontal axis, with the plough displaying the highest vibration. Optimal combination between tractor and implement, tractor and speed as well as 3-point shock absorbers (designed for the implements) were suggested by the authors for attenuating the vibration levels. The significance of lateral vibration was also highlighted by [PERSON] et al. [48]. They inferred that the lateral vibration levels can be higher than the vertical ones, while the former tend to increase linearly with the height above the ground of the tractor seat. It was seen that a 30 cm reduction of the tractor seat height can decrease the lateral vibration by approximately 20%. In contrast, the vertical vibrations are hardly affected by the height above the ground. The adjustment of electronic speed on the vibration levels of a tractor was investigated by [PERSON] et al. [59]. The electronic regulator offers the opportunity for operation with a constant speed mode regardless of the load. Vibration levels on the seat were measured for the tractor driving on an asphalt road at different speeds, namely at 20, 25 and 28 km/h. The weighted acceleration was found to be larger for the case of electronic speed adjustment. Conversely, during cultivating at various speeds, namely at 6, 7.5 and 9 km/h, the vibration by utilizing the speed adjustment were observed to be lower comparing to the normal operation. The effect of different speeds as well as various surfaces with different tire pressures and tractor masses was investigated by [PERSON] et al. [60]. In particular, the vibration values along with acceleration transmissibility concerning the three axes were estimated on both the seat and the cabin platform. This investigation demonstrated that the accelerations of the seat along the x and y axes are affected by the pitching and rolling movements. According to authors, manufacturers should decrease these implications by using suspension systems in these directions. [PERSON] et al. [19] carried out a laboratory-based investigation in order to evaluate the effect of a single- and multi-axial suspension seat on lessening the exposure to WBV and physical fatigue of the major muscles of neck and low back during driving agricultural tractors. To this end, a motion platform simulated the tractor environment by applying the 24-minute field-measured profiles of vibrations. These data appertained to smooth paved and gravel roads, farm fields and extravagant off-road terrain. The outcomes showed that the multi-axial consideration can reduce the lateral vibration exposures and the associated muscular fatigue in the low back and the neck. The effect of the type of the terrain was also examined in [61], which aimed at assessing the convenience of tractor seats during harrowing and having while driving the tractor on ridges and asphalted surface. Moreover, an approach relied on the pressure mapping was utilized to evaluate the comfort of the seats. The derived pressure indices were considered to be particularly useful tools for the seat mapping and comparing the seats that are available on market on the basis of the buttocks-seat interface under dynamic circumstances. The influence of vibrations on the tractor operator was also investigated by biomechanical models in [62; 63]. [PERSON] & [PERSON] [62] estimated the compressive and shear loads on the tractor operator lumbar vertebra while seating with different cushion materials for the back. Seven seat cushion materials with various thicknesses and compositions were tested. The maximal compressive forces were observed for the case of coir cushion having a thickness of 80 mm, whereas the minimum ones appeared when a high-density polyurethane foam was utilized with a thickness of 44 mm.