Forced Postures in Courgette Greenhouse Workers

: Occupational health and safety allows the prevention of occupational diseases and accidents. Agriculture is one of the sectors in which it is important to prevent the musculoskeletal disorders that workers usually develop. The objective of this study is the evaluation of postures adopted by courgette farmers in greenhouses of the Almeria-type. OWAS (Ovako Working Posture Assessment System), an ergonomic evaluation method, is used and applied after making observations to the postures adopted by the workers who were previously video recorded. The results concluded that the four risk levels established by OWAS appeared, with 37.14% being the highest rate and belonging to risk level 2, 33.33% to risk level 1, 28.57% to risk level 3, and 0.95% to risk level 4. Therefore, depending on the severity of the postures adopted in each task, the need for changes in a short, medium, or long period of time was concluded.


Occupational Health and Safety
The concept of occupational health and safety is defined as the "conditions and factors that affect, or could affect, the health and safety of employees or other workers (including temporary workers and contractor personnel), visitors, or any other person in the work area" [1].
Companies implement health and safety management systems for their workers [2]. The implementation of these management systems allows the prevention of occupational diseases and accidents. In addition, it contributes to achieve numerous improvements in companies related to aspects such as competitiveness, the involvement of workers in the company thanks to their motivation, and cost reduction [3].
Musculoskeletal disorders are one of the most common occupational diseases. The prevention of these disorders positively affects companies and the health of workers [4].

Musculoesqueletal Disorders
Work-related musculoskeletal disorders (MSD) are a serious problem frequently developed in workers of many fields [5].
This type of disorder can appear in different body parts, the most common being the back, shoulders, neck, and upper extremities [4]. Workers are exposed to different risks in their jobs that can contribute to develop these disorders. Some of these risks are, for example, the adoption of forced postures, the performance of repetitive tasks, the handling of loads, the exposure to vibrations, the extreme temperatures in their workplace, etc. [4].
Finally, this type of disorders has numerous consequences [6]: • For the workers who suffer them, encompassing not only physical, but also mental, aspects, due to not feeling able to continue doing a job.

•
For the economy of workers, since they sometimes cannot continue in their jobs due to the type of developed disorders.

•
For the economy of companies and countries. In companies, musculoskeletal disorders cause productivity to decrease and sick leave to rise.

Musculoskeletal Disorders in Southeastern Spain Agriculture
In the agricultural sector, there are a small number of studies dedicated to the investigation of occupational diseases that are common among workers, including musculoskeletal disorders [7]. However, in this area there are numerous risks that farmers are facing during the performance of their tasks and that can contribute to the appearance of these type of disorders [8].
The province of Almeria is characterized by a large area of greenhouses, where different crops are grown, employing approximately 55,000 workers. Several studies conclude that there are numerous musculoskeletal disorder symptoms among workers in these greenhouses [9].
Two research studies have already been carried out on this type of occupational diseases that occur in greenhouse farmers in Almeria. In one study, the Standardized Nordic Questionnaire [10] was used to analyze musculoskeletal disorders in farmers and some variables related to the worker (sex, height, weight, etc.) and to the cultivation (area, type, etc.) were considered. The results concluded a high rate of MSD [9]. Another study was carried out to analyze the MSD in melon cultivation workers. In this, an ergonomic evaluation method called OWAS (Ovako Working Posture Assessment System) [11] was used, which concluded the risks implied by the postures adopted in each task [12].

Evaluation Methods
There are several ergonomic assessment methods aiming the prevention of occupational musculoskeletal disorders. These methods can be classified intro three types [5]: • Direct. Based on the use of sensors. An example of this type of method is the HADA Move-Human sensor system [13]. • Semi-quantitative. They use evaluation software and a previous observation of the workers performing tasks. Some examples of these methods are: RULA method [14], REBA (Rapid Entire Body Assessment) method [15], OWAS method [11], Snook and Ciriello tables [16], etc. • Qualitative. Use of questionnaires. Examples of these methods are the Standardized Nordic Questionnaire [10], the Quick Exposure Check [17], etc.

Objective
The objective of this study is the evaluation of the adopted postures by farmers during the courgette cultivation in Almeria-type greenhouses.

Greenhouse
The greenhouse where the study was conducted is located in the province of Almeria and has the characteristics that are shown in the following table (Table 1).

Material Used
The material used consists of a PD Pentaxdigital-DPV9000 video camera (Pentax, Tokyo, Japan), with a resolution of 12 megapixels and an 8× digital zoom.
On the other hand, to know the height and weight of the workers, we use: • An Evel measuring tape (Buenos Aires, Argentina) with a length of 3 m and accuracy of ±0.1 mm.

•
A Kern MFB 150K100 scale (Balingen, Germany) with a maximum weighing field of 150 kg and a reproducibility of 0.8 kg.

Workers
In this crop the work is developed by two workers, a woman of 44 years (height = 1.61 m, weight = 72 kg) and a man of 47 years (height = 1.65 m, weight = 75 kg). Therefore, the sample of workers that has been employed in this study is of two workers belonging to the same greenhouse. This is because the objective of the study was not to investigate the consequences of performing tasks on workers with different characteristics, such as age, sex, etc., but to evaluate the postures that are usually adopted for courgette cultivation.
The postures that are adopted in each one of the courgette cultivation tasks are always very similar in Southeastern Spain, since the tasks carried out are always the same. This study focuses on the evaluation of these positions, regardless of the worker who develops them.

Evaluation Method
In order to decide which method will be used, five observation methods that could be interesting for this study are described: CORLETT (Posture Targeting) [18], OWAS (Ovako Working Posture Assessment System) [11], REBA (Rapid Entire Body Assessment) [15], VIRA (This method is from National Board of Occupational Safety and Health, Sweden) [19] and ARBAN (Ergonomic Analysis) [20].
• CORLETT: this method evaluates the positions of ten body areas (head, trunk, lower and upper extremities) with respect to a reference position. The method is simple, precise, and reproducible. It is not appropriate for postures that are adopted during short time intervals and that are not repeated. It does not consider the load, the posture's duration, or the frequency with which they are adopted [18,21]. • OWAS: this method allows to evaluate 252 postures. These are the result of combining four positions for the back, three positions for the arms, seven positions for the legs, and three intervals corresponding to the load supported. It is a reliable and frequently used method. In addition, there is a lot of information related to OWAS. It does not evaluate the positions of the neck, wrists, and elbows and does not evaluate the right and left part of the body independently [11,21,22].
• REBA: It allows evaluate the trunk, neck, legs, arms, forearms and wrists. It also considers the load, the grip, and the type of physical activity. It is a simple method and it does not take long in its application. It does not consider the frequency or duration of postures. The right and left hand are analyzed independently [15,21]. • VIRA: This method evaluates the neck and arms. It is a simple method, appropriate for tasks that are repetitive, with a short time interval. It does not evaluate the trunk, hands, and leg postures. It cannot be used when handling important loads. It takes a long time to be applied [19,22]. • ARBAN: This method evaluates neck, trunk, arms, and legs using the Borg scale. It is focused on the evaluation of ergonomic stress. It is easy to understand the results obtained. It does not consider the load and one of its limitations is the time necessary to apply it [20][21][22].
The VIRA method was the first to be discarded because it only focuses on evaluating two parts of the body: the neck and arms. The second factor considered was the load. OWAS and REBA are the only methods that consider the load. An important difference between these methods is that OWAS is a method that allows a general evaluation of the postures, since these are selected in the observation according to a certain time interval [21,22]. On the contrary, REBA is not used for a general evaluation, but to evaluate the positions considered more harmful or frequent [21]. Therefore, in line with the study objective (the evaluation of the adopted positions), the most appropriate method is OWAS. The REBA method could be used in more specific studies in which it is not intended to evaluate all the postures.

Ovako Working Posture Assessment System Method
The OWAS method originated in Finland, specifically in the steel industry. Its usefulness is based on the evaluation of the postural load on workers during the performance of their tasks [11].
This method is able to detect a total of 252 different postures by combining the assessed position of each of the three parts of the body, with the weight of the load handled by the worker. The method identifies four positions for the back, three positions for the arms, seven positions for the legs, and three values for the weight of the handled load, thus achieving the 252 possible combinations as mentioned above [11].
To apply this method in the courgette cultivation, the following stages are settled [11]. First, the observation of the postures performed by workers during the different tasks is carried out. This can be done by recording videos. In this case study, intervals of 5, 10, and 15 s will be used in order to cover most of the postures they perform. For each of these postures, the position of the back, legs and arms and the weight of the load supported is identified, obtaining a four-digit code (Appendix A). The method calculates the risk category corresponding to each posture and to each part of the body ( Table 2). Table 2. OWAS method risk levels [12]. It is possible to use numerous software to apply the OWAS method. In this case the software used is Ergomet 3.0. (MAPFRE ergonomics institute, Madrid, Spain) [23].

Identification of Agricultural Tasks during Courgette Cultivation in Almeria-Type Greenhouses
The observation allows to identify all the tasks in the courgette cultivation. A total of 10 tasks were observed. These were divided into 6 work phases. In the selection of the postures of each task, intervals of 5, 10, and 15 s were used. The observation was made in several working days, according to the day in which the farmers developed each task. The duration of the courgette cultivation was four months ( Table 1).
The agricultural tasks (not maintenance or auxiliary) identified in the experimental stage and practiced to the courgette cultivation are shown in Table 3: Table 3. Identification of tasks in courgette cultivation.

Work Phases Agricultural Tasks Description
Transplanting Agronomy 2019, 9, x FOR PEER REVIEW 6 of 20 Table 3. Identification of tasks in courgette cultivation.

Work phases Agricultural tasks Description
Transplanting • Removing sand Using a weeding hoe, the sand is removed and a hole is made. In this hole, the root ball is inserted, covered and watered. •

Making holes
• Transplanting

Aerating soil
• Aerating soil Using a rectangular scraper the layer of the sand surface is broken. After a few days, a fine crust is formed. In this way, the soil is oxygenated, avoiding weeds sprouting.

Spraying
The worker uses a spraying backpack and walks between the cultivation lines to apply the product on the crop.

• Harvesting
A manual harvest is carried out. Cutting tools are used to cut courgettes. For the collection, a cart with boxes is used. The boxes are piled up in the greenhouse corridor, being subsequently removed manually or with a tractor. They are also piled on pallets and forklifts are used.

Stringing
• Stringing A string is hooked to the grate and to the lower part of the plant.
• Removing sand Using a weeding hoe, the sand is removed and a hole is made. In this hole, the root ball is inserted, covered and watered.

Aerating soil
Agronomy 2019, 9, x FOR PEER REVIEW 6 of 20 Table 3. Identification of tasks in courgette cultivation.

Work phases Agricultural tasks Description
Using a weeding hoe, the sand is removed and a hole is made. In this hole, the root ball is inserted, covered and watered. •

Making holes
• Transplanting • Covering holes

Aerating soil
• Aerating soil Using a rectangular scraper the layer of the sand surface is broken. After a few days, a fine crust is formed. In this way, the soil is oxygenated, avoiding weeds sprouting.

Spraying
The worker uses a spraying backpack and walks between the cultivation lines to apply the product on the crop.

• Harvesting
A manual harvest is carried out. Cutting tools are used to cut courgettes. For the collection, a cart with boxes is used. The boxes are piled up in the greenhouse corridor, being subsequently removed manually or with a tractor. They are also piled on pallets and forklifts are used.

Stringing
• Stringing A string is hooked to the grate and to the lower part of the plant.
• Aerating soil Using a rectangular scraper the layer of the sand surface is broken. After a few days, a fine crust is formed. In this way, the soil is oxygenated, avoiding weeds sprouting.

Spraying
Agronomy 2019, 9, x FOR PEER REVIEW 6 of 20 Table 3. Identification of tasks in courgette cultivation.

Work phases Agricultural tasks Description
Using a weeding hoe, the sand is removed and a hole is made. In this hole, the root ball is inserted, covered and watered. •

Making holes
• Transplanting

Covering holes
Aerating soil • Aerating soil Using a rectangular scraper the layer of the sand surface is broken. After a few days, a fine crust is formed. In this way, the soil is oxygenated, avoiding weeds sprouting.

Spraying
The worker uses a spraying backpack and walks between the cultivation lines to apply the product on the crop.

• Harvesting
A manual harvest is carried out. Cutting tools are used to cut courgettes. For the collection, a cart with boxes is used. The boxes are piled up in the greenhouse corridor, being subsequently removed manually or with a tractor. They are also piled on pallets and forklifts are used.

Stringing
• Stringing A string is hooked to the grate and to the lower part of the plant.

• Spraying
The worker uses a spraying backpack and walks between the cultivation lines to apply the product on the crop. Table 3. Identification of tasks in courgette cultivation.

Work phases Agricultural tasks Description
Using a weeding hoe, the sand is removed and a hole is made. In this hole, the root ball is inserted, covered and watered. •

Making holes
• Transplanting

Covering holes
Aerating soil • Aerating soil Using a rectangular scraper the layer of the sand surface is broken. After a few days, a fine crust is formed. In this way, the soil is oxygenated, avoiding weeds sprouting.

Spraying
The worker uses a spraying backpack and walks between the cultivation lines to apply the product on the crop.

• Harvesting
A manual harvest is carried out. Cutting tools are used to cut courgettes. For the collection, a cart with boxes is used. The boxes are piled up in the greenhouse corridor, being subsequently removed manually or with a tractor. They are also piled on pallets and forklifts are used.

Stringing
• Stringing A string is hooked to the grate and to the lower part of the plant.

• Harvesting
A manual harvest is carried out. Cutting tools are used to cut courgettes. For the collection, a cart with boxes is used. The boxes are piled up in the greenhouse corridor, being subsequently removed manually or with a tractor. They are also piled on pallets and forklifts are used.

Work phases Agricultural tasks Description
Transplanting • Removing sand Using a weeding hoe, the sand is removed and a hole is made. In this hole, the root ball is inserted, covered and watered. •

Covering holes
Aerating soil • Aerating soil Using a rectangular scraper the layer of the sand surface is broken. After a few days, a fine crust is formed. In this way, the soil is oxygenated, avoiding weeds sprouting.

Spraying
The worker uses a spraying backpack and walks between the cultivation lines to apply the product on the crop.

• Harvesting
A manual harvest is carried out. Cutting tools are used to cut courgettes. For the collection, a cart with boxes is used. The boxes are piled up in the greenhouse corridor, being subsequently removed manually or with a tractor. They are also piled on pallets and forklifts are used.

Stringing
• Stringing A string is hooked to the grate and to the lower part of the plant.
• Stringing A string is hooked to the grate and to the lower part of the plant.

Plant removal
Agronomy 2019, 9, x FOR PEER REVIEW 7 of 20 The previously placed strings are untied manually to unhook the plants, but they are left hooked so that they can be removed by pulling the strings. They are placed in the greenhouse, in the main corridor, then loaded onto a cart and removed from of the greenhouse. • Greenhouse plant removal

Data Analysis
In this study two different software packages, SPSS v.23 (International Business Machines Corporation, Armonk, New York) and XLSTAT (2018, Addinsoft, Paris, France), are used in order to analyze the sample data. A descriptive analysis of the different variables corresponding to the OWAS method is carried out. In addition, a multiple correspondence analysis is also performed. The The previously placed strings are untied manually to unhook the plants, but they are left hooked so that they can be removed by pulling the strings. They are placed in the greenhouse, in the main corridor, then loaded onto a cart and removed from of the greenhouse.
• Greenhouse plant removal

Data Analysis
In this study two different software packages, SPSS v.23 (International Business Machines Corporation, Armonk, New York) and XLSTAT (2018, Addinsoft, Paris, France), are used in order to analyze the sample data. A descriptive analysis of the different variables corresponding to the OWAS method is carried out. In addition, a multiple correspondence analysis is also performed. The variables used are the following: Posture code (PC), Arms (A), Back (B), Legs (L), Load (Q), Task (T), Risk (R), and Risk combination (RC). This last variable refers to different groupings that may occurs between risk levels 1, 2, 3, and 4. The names that have been established for the different categories of these variables are summarized in Appendix B (Table A1). In the present study, it is interesting to complement the descriptive analysis of the variables with the nominal categorical data analysis technique of the multiple correspondence analysis because it allows the detection and representation of the underlying structures in the dataset. This study allows representing how the different categories of the studied variables are correlated, by means of a two-dimensional model or axes. This will allow to know as a whole, which cultivation task is associated with a certain position or positions of the back, arms, and legs, as well as with the load handled by the worker, and all this associated with the risk provided by the OWAS method and the possible combination of these risks.

Results of the Whole Courgette Cultivation
In the study, 105 observations have been made. To each of these corresponds a posture and to each posture a photographic snapshot. Figure 1 differentiates the risk categories arising when assessing all the postures adopted by the workers during the entire courgette cultivation. The results show that 100% of the postures made during the cultivation are classified in the four risk categories. The highest rate, with a value of 37.14%, belongs to risk level 2. This is followed by 33.33% of the postures with risk level 1. Finally, 28.57% and 0.95% correspond to risk levels 3 and 4, respectively.
greenhouse. plant removal

Data Analysis
In this study two different software packages, SPSS v.23 (International Business Machines Corporation, Armonk, New York) and XLSTAT (2018, Addinsoft, Paris, France), are used in order to analyze the sample data. A descriptive analysis of the different variables corresponding to the OWAS method is carried out. In addition, a multiple correspondence analysis is also performed. The variables used are the following: Posture code (PC), Arms (A), Back (B), Legs (L), Load (Q), Task (T), Risk (R), and Risk combination (RC). This last variable refers to different groupings that may occurs between risk levels 1, 2, 3, and 4. The names that have been established for the different categories of these variables are summarized in Appendix B (Table B1). In the present study, it is interesting to complement the descriptive analysis of the variables with the nominal categorical data analysis technique of the multiple correspondence analysis because it allows the detection and representation of the underlying structures in the dataset. This study allows representing how the different categories of the studied variables are correlated, by means of a two-dimensional model or axes. This will allow to know as a whole, which cultivation task is associated with a certain position or positions of the back, arms, and legs, as well as with the load handled by the worker, and all this associated with the risk provided by the OWAS method and the possible combination of these risks.

Results of the Whole Courgette Cultivation
In the study, 105 observations have been made. To each of these corresponds a posture and to each posture a photographic snapshot. Figure 1 differentiates the risk categories arising when assessing all the postures adopted by the workers during the entire courgette cultivation. The results show that 100% of the postures made during the cultivation are classified in the four risk categories. The highest rate, with a value of 37.14%, belongs to risk level 2. This is followed by 33.33% of the postures with risk level 1. Finally, 28.57% and 0.95% correspond to risk levels 3 and 4, respectively.

Results according to the Courgette Cultivation Tasks
Of the 105 observations taken, nine are from "Removing sand", 6 from "Making holes", 10 from "Transplanting", seven from "Covering holes", eight from "Aerating soil", six from "Spraying", 19 from "Harvesting", 15 from "Stringing", 10 from "Plant unstringing", and 15 from "Greenhouse plant removal". Below, the results obtained for these observations are shown depending on agricultural tasks ( Table 4). The table shows the codes for the postures adopted by the workers, the repetition rate of these, and risk level to which they belong represented in colors. The meaning of posture codes can be found in Appendix A. On the other hand, Table 5 shows the total rates and the relative frequencies of each risk according to the task.
Risk level 1 is presented in seven of the 10 tasks, identifying the highest rates in the tasks of "Spraying" and "Plant unstringing" with 100% in both. Risk category 2, also differ in seven of the 10 tasks. For this, the highest rates of postures are found in "Removing sand" and "Aerating soil", with 88.89% and 87.50%, respectively. Risk level 3, appears in 6 of the 10 tasks evaluated, being in a greater rate in "Covering holes", specifically with a rate of 57.14%. Finally, risk level 4 only occurs in a task of the studied ones ("Harvesting"), with 5.26%. As shown (Table 4), the highest risk level (level 4) is identified only in a position of all those evaluated. Therefore, the most damaging posture that the worker performs is with the bent and twisted back, arms below shoulder level, standing or squatting two bent legs, and load less than 10 kg (4141), with a repetition rate of 5.26%. This posture is adopted in the "Harvesting" task. Other harmful postures identified in this cultivation belong to risk level 3. It consists of 14 postures that appear in 6 cultivation tasks. Some of those that present a higher repetition rate in the tasks are: • The bent back, arms at or above shoulder level, standing or squatting two bent legs, and load less than 10 kg (2341), with a rate of 28.57%, in the "Covering holes" task.

•
The bent back, arms at or above shoulder level, standing or squatting two bent legs, and load less than 10 kg (2341), with a rate of 46.67%, in the "Stringing" task.

•
The bent back, arms below shoulder level, standing or squatting two bent legs, and load less than 10 kg (2141), with a rate of 26.67%, in the "Greenhouse plant removal" task.
The positions belonging to risk level 2 are not as damaging as the previous ones. The research shows that the predominant risk is risk level 2. For example, this risk appears in the posture with the bent back, arms below shoulder level, standing on two straight legs and load less than 10 kg (2121), with rate of 55.56%, in the "Removing sand" task.
Finally, the postures that correspond to a risk category 1 are normal positions, they are not harmful to the worker.
On the other hand, Table 5 shows the total rates and the relative frequencies of each risk according to the task. Risk level 1 is presented in seven of the 10 tasks, identifying the highest rates in the tasks of "Spraying" and "Plant unstringing" with 100% in both. Risk category 2, also differ in seven of the 10 tasks. For this, the highest rates of postures are found in "Removing sand" and "Aerating soil", with 88.89% and 87.50%, respectively. Risk level 3, appears in 6 of the 10 tasks evaluated, being in a greater rate in "Covering holes", specifically with a rate of 57.14%. Finally, risk level 4 only occurs in a task of the studied ones ("Harvesting"), with 5.26%.

Results according to Body Parts and Weight of the Handled Load for the Entire Courgette Cultivation
Using the OWAS method it is also possible to obtain the results of relative frequency or repetition rate and risk level for each body parts.
For the entire courgette cultivation a total of 105 postures are observed. The results show that the most harmful postures adopted (risk level 2) were for the bent back and standing or squatting on two bent legs, with a repetition rate of 64.76% and 19.05%, respectively (Table 6).
Finally, the load weights less than 10 kg in most of the adopted positions (80.95%). On the other hand, Table 5 shows the total rates and the relative frequencies of each risk according to the task.
Risk level 1 is presented in seven of the 10 tasks, identifying the highest rates in the tasks of "Spraying" and "Plant unstringing" with 100% in both. Risk category 2, also differ in seven of the 10 tasks. For this, the highest rates of postures are found in "Removing sand" and "Aerating soil", with 88.89% and 87.50%, respectively. Risk level 3, appears in 6 of the 10 tasks evaluated, being in a greater rate in "Covering holes", specifically with a rate of 57.14%. Finally, risk level 4 only occurs in a task of the studied ones ("Harvesting"), with 5.26%.

Results according to Body Parts and Weight of the Handled Load Based on the Courgette Cultivation Tasks
Next, the results are presented for each body part, but in this case according to the agricultural task ( Table 7).
The greatest risk for the back is when it is bent. This happens in four tasks, "Removing sand", "Transplanting", "Covering holes", and "Aerating soil", all with a repetition rate of 100%, except for the last one with an 87.50%. The rest of the back positions present lower risk categories, with levels 2 and 1.
In the case of the arms, the highest risk level is also 3, found in the task of "Stringing" when both arms are above shoulder level, and with a repetition rate of 86.67%.
For the last part of the body evaluated, the legs, the highest risk level is 3, as in the two previous cases. This category appears in the position of bent knees, in two particular tasks, "Covering holes" and "Stringing" with repetition rates of 57.14% and 44.67%, respectively.
Finally, in six of the 10 tasks the load weighs less than 10 kg for the 100% of the cases. The other higher rate, also a 100%, is observed in the "Spraying" task with the load weight included in the range between 10 and 20 kg. For the third range, in which the load weighs more than 20 kg, there is a repetition rate of 33.33% in the "Greenhouse plant removal" task. On the other hand, Table 5 shows the total rates and the relative frequencies of each risk according to the task.
Risk level 1 is presented in seven of the 10 tasks, identifying the highest rates in the tasks of "Spraying" and "Plant unstringing" with 100% in both. Risk category 2, also differ in seven of the 10 tasks. For this, the highest rates of postures are found in "Removing sand" and "Aerating soil", with 88.89% and 87.50%, respectively. Risk level 3, appears in 6 of the 10 tasks evaluated, being in a greater rate in "Covering holes", specifically with a rate of 57.14%. Finally, risk level 4 only occurs in a task of the studied ones ("Harvesting"), with 5.26%.

Workdays Related to the Courgette Cultivation
Based on the observation of the videos recorded during the courgette cultivation, the seconds that the worker spends performing a cycle for every task can be obtained. Some tasks, such as harvesting and plant removal, are divided into two parts (Table 8). The results of the total workdays and hours ( Table 9) that a worker spends on each task for courgette cultivation are shown below. These results are obtained from Tables 1 and 8. In addition, a correction factor (fc = 1.20) is considered for each agricultural task, which considers time relative to breaks, preparation of tools, etc.

Multiple Correspondence Analysis
By performing multiple correspondence analysis, it is possible to obtain the correlations of the categories of the variables. The model that has been obtained after this analysis presents two significant dimensions (Table 10). In this table the values of the variance, the Cronbach's coefficient (α), and the eigenvalue are shown. Since the Cronbach's coefficient is 0.878 and the mean eigenvalue is 4.314, the reliability of the model is considered good. Each of the two dimensions represents a factorial axis that gives information about the original study variables that are most associated with each other. This is quantified by the discrimination measures of each variable. Table 10 also shows the discrimination measures. Regarding the model mean, the variable with the highest value is PC (0.948), followed by T (0.749), RC (0.710), R (0.669), B (0.515), L (0.341), and A (0.233), and ending with the least explanatory one, which is Q (0.150). It is also observed in Table 10 that in dimension 1 the maximum value is that of variable PC (0.974) and the minimum value is that of variable A (0.080), and for dimension 2, the maximum and minimum values are for variables PC (0.922) and Q (0.018), respectively. Dimension 1 (horizontal axis) can discriminate with a gradient of values from more positive to more negative in the categories of the variables PC, R, and B as represented in Figure 2. Dimension 2 (vertical axis) better discriminates the referred gradient of values, but on the vertical axis, in the categories of variables PC and T. From Table 10 it can be deduced that the value of each dimension discriminates more the closer it is to the value 1. The multiple correspondence model made allows the identification of the categories of each variable that discriminates the objects (sample unit) and, therefore, the quantifications of the variables are obtained. Graphically, this fact can be observed in Figure 2. respectively. Dimension 1 (horizontal axis) can discriminate with a gradient of values from more positive to more negative in the categories of the variables PC, R, and B as represented in Figure 2. Dimension 2 (vertical axis) better discriminates the referred gradient of values, but on the vertical axis, in the categories of variables PC and T.  Table 10 it can be deduced that the value of each dimension discriminates more the closer it is to the value 1. The multiple correspondence model made allows the identification of the categories of each variable that discriminates the objects (sample unit) and, therefore, the quantifications of the variables are obtained. Graphically, this fact can be observed in Figure 2.  Table B1, see Appendix B).
Next, Table 11 shows the quantifications of the most representative categories that best explain the positive and negative values in each dimension, for each of the variables.  Table A1, see Appendix B).
Next, Table 11 shows the quantifications of the most representative categories that best explain the positive and negative values in each dimension, for each of the variables.

Discussion about the OWAS Method Results
The results indicate that farmers adopt postures distributed mainly among the first 3 levels or risk (Table 4). This coincides with another research made about melon cultivation in Almería within greenhouses with "backbone" structures [12]. Obviously, these facts require actions (see Appendix C) aimed at minimizing musculoskeletal risk [9].
By work phases, in "Transplanting" (Table 4) forced postures are performed (level 3), which also coincides with other studies [12,24]. In "Aerating soil" (bent back; Table 7), "Stringing" (both arms at or above shoulder level and standing or squatting on two bent legs; Table 7), "Harvesting" (bent back, standing or squatting on two bent legs, and standing or squatting on one bent leg; Table 7) and "Plant removal" (bent back and standing or squatting on two bent legs; Table 7) something similar happens, but with risk levels between 2 and 3. These disorders and other incorrect postures of the trunk, wrist, and neck have also been described by other authors [12,[25][26][27][28][29][30].

Discussion about Results Related to Workdays
In Almeria (SE Spain) an agricultural work unit is equivalent to 320 workdays/hectare for nine months of cultivation [31].
According to the previous data, the theoretical data that would be obtained for the present study with a courgette cultivation area of 8400 m 2 , would be 268.8 workdays for nine9 months. Therefore, workdays for four months would be 119.5.
If this theoretical value of 119.5 workdays is compared with the real one of 130.66 workdays obtained in the results statement (point 3.5), it can be deduced that they are close values. The difference between both values could be due to periods dedicated to irrigation, arrangements, etc.
During all the time the workers are performing some of the tasks described these workers will be exposed to risk levels between one and four, which highlights one of the limitations of the OWAS method. This method does not consider the total exposure time per evaluated task [5]. Figure 2 shows how certain courgette cultivation tasks are associated with a certain risk level of suffering musculoskeletal risks, as well as the position of the back, arms, and legs, as occurs with melon cultivation in greenhouses in Almería [12]. Thus, for positive values of both dimensions, it is observed how the tasks "Covering holes" and "Harvesting" of courgettes are associated with a high risk level, up to type 3 in the first case and up to type 4 in the second case, which is due to the fact that a posture is adopted with knees and legs flexed, as has been described for other crops, such as melon [12,29,30], tomato [27,28], and pepper [27]. Likewise, for positive values of dimension 1 and negative values of 2, it is observed, as well as for courgette, that the tasks "Transplanting" and "Removing sand" are associated with postures, such as the bent back (forced) and both arms below shoulder level, with a combination of risks 2 and 3. Although for melon cultivation in Almeria [12] the task "Transplanting" was associated only with risk 2, that is, a lower risk than for courgettes. For rice cultivation [24], musculoskeletal disorders associated with the "Transplanting" task have also been identified. On the other hand, for negative values in both dimensions in courgette, it is observed that the task "Making holes" is associated with a posture of standing on two straight legs, as has been observed for melon [12], pepper, and tomato [27] cultivation, which also involves a combination of risk 1 and 2 in courgette. Finally, the tasks of "Spraying" and "Plant unstringing" are associated with a straight back posture and risk level 1.

Strengths and Limitations of the Study
The OWAS method allows carrying out an assessment by observation, not requiring the use of sensors or other means that could disturb, distract or make workers waste their time during the performance of their tasks. Regarding the limitations, the OWAS method establishes that observations must be done in periods of time between 30 and 60 s. In this case, observations are made on periods of 5, 10, and 15 s, because different postures are adopted continuously in these tasks. It does not consider the worker's total exposure time in each task.

Conclusions
The findings discovered in this study show that farmers growing courgettes are exposed to musculoskeletal disorders because during the tasks they perform, many of the postures they adopt are injuring.
Therefore, since these postures that need to be corrected have been identified, corrective and preventive measures should be established to reduce or even prevent the appearance of these types of occupational diseases that are so common in the agricultural sector.
The main measures can be based on the use of tools that can replace or help the work made manually, and the reorganization of tasks, looking for solutions to carry them out in a healthy and safe way.

Conflicts of Interest:
The authors declare no conflict of interest.

Appendix A
The following are the posture codes established by the OWAS method. This method codes the back, arms and legs positions, and the load held by workers, forming a 4-digit code [11].  Appendix B Table A1. Variables and variables categories analyzed in the multiple correspondence analysis.

Variables Categories Coding
Cultivation task (T)

Appendix C
Some general recommendations to avoid the risk of developing musculoskeletal disorders would be [9,32,33]:

1.
Tasks should be performed at a height adjusted to workers, using, for example, tools with extensible handles, stools, etc.

2.
Workers should alternate between standing and sitting postures, in those tasks which could be possible.

3.
In repetitive actions, farmers should take breaks during their performance or alternate with other tasks.

4.
The use of means, such as carts, wheelbarrows, etc., should be done.

5.
Distribute the courgettes among several boxes, so that they do not weigh as much. In addition, boxes must have a good grip, so that the worker does not find very difficult to pick them up. 6.
The loads must be brought close to the body before lifting them. Another recommendation is to alternate this task with others of a different type.