3.3. Identification of the Main Risk Factors for the Development of MSDs
Agricultural manual operations usually include a plethora of physically demanding tasks that, most of the time, entail a combination of material handling, high muscular force, and postural load [78
]. The manual activities are carried out under adverse weather conditions, frequently on muddy grounds (usually with bare feet), and awkward postures. Even in developed nations, there are some cultivations, such as vegetable production, that remain highly dependent on manual labor [8
]. The journal papers, which were selected according to the limitations presented in the section of “Methods”, are summarized in Table 1
in chronological order. Moreover, they are classified according to the investigated manual operation, the type of crop, the followed method, and the main risk factors identified for MSDs. In this fashion, it should be stressed that review papers, such as in [79
], contained studies conducted before 2010 and were, therefore, not considered eligible for their inclusion in the present bibliographic review.
Obviously, according to Table 1
, out of the 27 accepted journal papers, the most highly examined manual operation during the last decade was the activity of harvesting (51.9%). The second considered tasks were the load carrying (11.1%) as well as the examination of multiple tasks taking place in agriculture (11.1%). Pruning followed (7.4%), with planting, digging, peeling (of pineapples), sorting, and weeding coming next (3.7%), with one study presented for each of them. The content as well as the dangers, in terms of exposure to MSDs, involved in each task was described in the corresponding subsections in 3.2. Concerning the crops that were involved in the accepted papers, there was a variety of crops ranging from apples, oranges, and grapes, to low-growing crops such as vegetables, rice, melons, and strawberries. This observation demonstrates that all types of cultivations can cause MSDs to workers. Remarkably, low-growing crops constituted the majority of the studies presented in Table 1
. These low heights of growing crops force the workers to stoop and kneel, in an iterative manner, with the intention of reaching them, thus, contributing in the onset of low back disorders and knee OA. The distribution of the agricultural manual operations according to the 27 selected investigations can be depicted in the pie chart of Figure 5
The majority of the selected studies adopted interviews and special questionnaires, with the standardized Nordic questionnaires being the main choice (44.4%) [80
]. Standardization is required in recording and analyzing the musculoskeletal symptoms. If not, it is very complicated to compare the findings of different investigations. In fact, questionnaires serve as instruments in order to scan MSDs for the benefit of work-related health care. The standardized Nordic questionnaire was designed so as to determine if MSDs take place among a given population and evaluate which of the nine selected body regions are affected mostly. Individuals have to answer to yes–no questions. More specifically, if the answer is “no”, the participant proceeds to another body part. If the answer is “yes”, the next questions take place that deal with duration, frequency, and medical intervention [81
]. 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, electrogoniometers (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
]. 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
]. Shin and Mirka [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. Furthermore, a field investigation during the harvesting of tomatoes by Miller and Fathallah [87
] found similar results by introducing a rest break of one minute after every eleven minutes of labor.
As it was highlighted above, the repetitive nature of agricultural tasks, which appeared in several of the selected papers (29.6%), enhances the probability for developing MSDs. Fatigue of muscles and joints is the way of the body telling us to alter our working pattern. Performing the same movement over and over again, by also using certain and usually awkward postures, seems to provoke inflammation and pain. Besides, most of the time, agricultural workers have to keep the neck and shoulders in a fixed position for the purpose of exerting some force required for the task. Awkward postures include twisting of the wrist or arm and overexertion. Repetitive motion disorders normally occur in the wrists, hands, elbows, and shoulders. However, they can also take place in the back, neck, and ankles. Repetitive fatigue in hip and knees can lead to painful OA that is very common in rural workers, as it was elaborated in the section of “Introduction”.
The third most reported risk factor, with prevalence of 22.2%, was age. In general, surveys have demonstrated higher frequency of reported MSDs for older farmers than younger ones. Many times, agricultural workers leave their job owing to suffering from MSDs. There is also a number of them who continue to work after retirement, especially in small and family farms. According to Cassou et al. [88
], biological changes associated with the aging process, namely, degenerative changes of ligaments, tendons, joints, and muscles, can result in the pathogenesis of MSDs. An overload regarding elderly farmers can be initiated because of the limited physical work capacity comparing to required workload. This may exacerbate the pathogenesis of MSDs [89
]. As a consequence, older workers are more likely to have injury complaints when compared with the younger ones.
The fourth most stated risk factor with incidence of 14.8% was the heavy carrying and lifting (abbreviated as HCL in Figure 6
). This type of manual operation entails prolonged heavy work which needs a lot of energy and strength. In the case of particularly bulky and heavy loads, even though a worker is able to lift the burden, strains are concentrated on the lifting contact, namely, the hands or fingers. Even in agricultural activities that do not involve heavy lifting, repetitive movements can increase the risk of MSDs [16
]. Some commercial products exist with the aim of reducing loads on low back during trunk bending by transferring load towards the legs. These ergonomics products are called weight (or load) transfer devices and have been the subject of the articles authored by Ulrey and Fathallah [35
]. Moreover, two ergonomic interventions, namely, “ergo bucket carrier” and “easy lift”, were successfully tested so as to handle water with buckets, which is very common in farms. Finally, an ergonomically designed bag was successfully tested instead of the currently used tied basket around the waist in coffee harvesting [47
Gender and kneeling were presented with equal prevalence (11.1%). Regarding the former, gender differences in the development of MSDs have been consistently reported in epidemiological investigations [90
]. For instance, women tend to have higher endurance, whereas they are more susceptible to movements that are low-load and repetitive. Besides, for the purpose of compensating their weaker strength, they may use the muscles at levels near their maximum capacity. The selected papers showed that women are more vulnerable to MSDs. As far as kneeling is concerned, which takes place during ordinary operations, such as harvesting, planting, weeding, and lifting, it can also lead to MSDs. Repetitive bending of the knee contributes to the development of knee OA as it was stressed above [19
]. Knee OA affects the whole joint, namely, the cartilage, the bones (both femur and tibia), and the synovial fluid (or synovium). In a healthy knee joint, the synovium is more viscous at low shear rates, whereas it becomes highly elastic for larger shear rates. This property allows it to protect the cartilage from wear by providing lubrication. In a diseased knee joint, however, its lubrication properties gradually degrade, mainly because of hyaluronic acid loss. Additional risk factors for developing of OA are female gender and obesity [18
]. Taking also into account that farmers tend not to visit a physician, old knee injuries, which have not be treated properly, can flare up again and hurt for the rest of their life. Of course, the same conclusion is drawn for all the MSDs.
Finally, exposure to pesticides, Body Mass Index (BMI), and inappropriate tools follow in the bar chart illustrated in Figure 6
with incidence of 7.4%, which corresponds to 2 papers. Pesticide poisoning constitutes a risk factor for several chronic health complications, as it may damage the nervous system, and thus intensify the pain perception [40
]. Exposure to pesticides was highly associated with chronic low back pain in [38
] regarding tobacco farmers. In addition, BMI, which is a measure of body adiposity, appears to be associated with the onset of MSDs [91
]. In general, individuals with an increased BMI tend to exhibit more musculoskeletal discomfort than those with a lower BMI. Finally, inappropriate tools that are either poorly maintained or not ergonomic require larger amount of energy. This fact, in conjunction with the repetitive nature of the activities, enhances the likelihood for developing MSDs.
In a nutshell, the present results revealed that prolonged stooping has been investigated in most of the studies (51.9%). Repetitive movements are certainly a considerable risk factor (29.6%) and are associated with the discomfort on low back, arms, and shoulders. Repetition is very risky because of the very short cycles, which are iterated during the working time. The age of the worker is also a notable risk factor (22.2%), as identified in several studies, as farmers use to work even though they are overage and usually having experienced a host of musculoskeletal injuries. Heavy lifting and Carrying (14.8%) (HCL) plausibly reported in the selected papers. Gender (11.1%) and Body Mass Index (7.4%) (BMI) are also personal characteristics which affect the development of MSDs. Kneeling (11.1%) was also identified, which is very common during agricultural activities and increases the risk of developing chronic knee pain and OA [92
]. Also, rarely maintained and non-ergonomically designed tools (7.4%) as well as pesticide exposure (7.4%) seem to contribute to musculoskeletal injuries. Another risk factor, however, with smaller incidence, was the working hours that demonstrated the need for frequent rest breaks. Finally, warming up, which has widely been examined in sports science to prepare soft tissues for the subsequent performance, can prevent the development of MSDs [74