# A Review on Ergonomics in Agriculture. Part I: Manual Operations
## 3 Results
### Identification of the Main Risk Factors for the Development of MSDs
In this fashion, it should be mentioned that the questionnaires by themselves cannot provide clinical diagnosis. However, careful filtering of the reported MSDs by experts can serve for analyzing the environment of the work and optimal tool design. One of the limitations of the questionnaires is that recent MSDs are more likely to be remembered compared with the older ones. Also, the filling out situation at that time as well as the environment can influence the results [80]. Electromyography (EMG) was also utilized in the experimental studies, which were selected for the present analysis with an incidence of 33.3%. In general, EMG is used for quantifying the muscle activity. Understanding how much and when the muscles are active during the required agricultural task is very useful for physicians for the purpose of understanding the mechanism of the injury and provide suitable treatment and rehabilitation protocols. Data from EMG do not always align with real muscle force, particularly as the velocity of muscle contraction increases [82]. Cameras (11.1%) were also utilized for recording the postures acquired by the participants in order to be carefully analyzed by experts. Moreover, electrogenometers (11.1%) were used, which convert the joint angle into a voltage, therefore making them suitable for measuring dynamic movements. Moreover, models were developed in three selected papers (11.1%) as an effort to simulate the real loads and motions occurring during agricultural operations. Also, other instruments, such as dynamometers, accelerators, and optical markers, were exploited. Finally, methodologies, such as Rapid Upper Limb Assessment (RULA) and OCcupational Repetitive Action (OCRA), were incorporated for evaluating the exposure of farmers to ergonomic risk factors. The risk factors for the development of MSDs, which are illustrated in Figure 6 in the form of a bar chart, were noted to be highly related to stooping, namely, the prolonged trunk flexion. This posture is inherent in a lot of rural activities that should be performed near the ground level. In particular, the identification of stooping as a risk factor was found in the majority of the selected papers (51.9%). Taking into account the adverse consequences of this body posture on the low back, it can be explained why low back injuries are of epidemic proportion among agricultural workers worldwide [8; 9; 59]. More specifically, stooping is commonly used for high-energy tasks, as the tissues of the back support the upper torso and, thus, lower the needs in postural energy and provide more energy for the agricultural operation [8]. Nonetheless, stooping together with the intensive heavy work escalates the low back pain to a great extent. From a biomechanical perspective, support of the lumbar spine during stooping is principally given by the passive viscoelastic connective tissues that gradually transfer loads from active muscles [83]. Sagittal bending of the trunk to maximal flexion includes the flexion-relaxation of the spine. Through this process, the active contraction concerning the muscles of lumbar extensor attains the physiological limit, whereas the flexion of the spine is entirely resisted via passive tissues [84]. Repetitive flexion of the spinal segments decreases the passive spinal tissue stiffness and enhances the intervertebral motion. This leads to the reduction of the intradiscal fluid amount. Considerable intradiscal fluid loss lessens the nucleus load-bearing capacity. This fact results in the loading transfer towards the sensitive fibers of annulus, thus causing higher stresses [8]. As a consequence, given that support during fully trunk bending is given from passive tissues, even small decrease of the stiffness of passive tissues, owing to sustained loading, can substantially diminish the stability of spine and escalate the vulnerability to injury [85]. [PERSON] and [PERSON] [86] showed that a short break of thirty seconds in the midst of ten minutes of continued flexion can reduce the consequences of the viscoelastic creep.