Identification of influential demographic and work-related risk factors associated to lower extremity pain perception among rice farmers

Abstract

BACKGROUND:

A high prevalence of musculoskeletal disorders and abnormal alignments of the lower extremities (LE) was found for rice farmers. It is important to investigate demographic and work-related risk factors associated with LE pain prior to developing intervention strategies addressing the problematic factors of the highest-risk task.

OBJECTIVE:

To identify factors associated with LE pain in rice farmers for every stage of the cultivation process.

METHODS:

Thirty experienced farmers (age of 45.9±6.21 (mean±SD)) rated LE pain experienced before and after each cultivation stage using the Standardized Nordic Questionnaire. Risk factors of pain were characterized based on expert risk assessment of tasks due to force, posture and motion, in addition to a conventional survey of demographic and other work-related information.

RESULTS:

Ergonomic risk factors were found to be the strongest predictors of knee and foot pain perception, which induced a substantial increase of pain perception (up to 4.6 times) with varying extent for individual cultivation stages. The highest risk and pain perception was found during the planting performance. Age exhibited significantly positive association with foot pain during planting and harvesting. However, more experienced farmers perceived less foot pain, presumably by developing effective movement strategies.

CONCLUSIONS:

The findings suggest that the planting process should be subject of further intervention development, especially for older farmers, with focus on reducing force, awkward posture and repetitive movement to minimize risk of LE pain.

Keywords

Agriculture risk assessment musculoskeletal pain

1 Introduction

Similar to many other Southeast Asian countries, industrial rice production in Thailand relies heavily on manual labour, employing only few advanced agricultural machinery. Most cultivation tasks involve strenuous activities and are primarily based on manual work efforts on heavy and viscous muddy work terrain, causing rice farmers to preferably perform these tasks with bare feet [1]. Not surprisingly, a high prevalence of musculoskeletal disorder (MSD) in the lower extremities (LE) was observed among Thai rice farmers (10.29–41.16%) [2]. Such LE MSDs are likely to cause chronic leg pain and malalignment, thus limiting work capability and requiring costly medicine and healthcare service [3, 4]. Indeed, a recent investigation of LE alignment revealed that rice farmers in Thailand exhibit a high prevalence of abnormal LE alignment (11.24% – 36.14%). To guide the development of effective intervention strategies, it is critical to initially investigate problematic factors associated with pain for specific LE parts during the performance of high-risk tasks.

The rice cultivation process can generally be divided into multiple stages: field preparation, seeding, planting, nursing and fertilization, and harvesting [5] (see Fig. 1). Each cultivation stage involves the usage of specific tools and requires different work postures, force exertions and movement patterns. During the first stage of rice cultivation, farmers perform the field preparation by using heavy vibrating machinery to plow the field while walking on a slippery, tilted surface. The seeding and fertilization processes involve lifting and carrying heavy loads together with prolonged walking on a muddy surface in shallow water. The planting task requires highly repetitive forward bending and lateral twisting of the trunk while standing on a muddy surface filled with water. Lastly, the harvesting activities involve prolonged stooping with trunk twisting and walking on dry and rough ground. Due to this variety of working conditions, individual cultivation steps are presumed to be associated with different levels of pain and risk of LE injury.

Fig.1

Typical stages of rice cultivation process: a) field plowing; b) seeding; c) planting; d) nursing and fertilization and; e) harvesting.

Work-related factors, including extended number of daily working hours, years of experience and ergonomic factors of force, postures, and motion, have also been found to be associated with LE MSDs [3 , 6–11]. Research related to agricultural work showed high force exertion during lifting or carrying loads over 5 kg to be a risk factor of LE MSDs [12]. Repeated exposure to soft tissue damage and joint degeneration may lead to abnormal biomechanical function and deviation from neutral body alignment, resulting in LE malalignment and pain [13]. Prolonged performance of awkward postures during farming work, including kneeling, stooping or bending, was identified as risk factor of knee and hip MSDs [14]. In addition, a previous study indicated extended repetition of stooping with twisting posture during planting activity to damage the knee joint and muscles of Thai rice farmers [15]. Extended daily working hours and years of farming experience on rice farming tasks may be correlated with perceived leg pain caused by excessive weight bearing in muddy soil, which increases leg joint loading and muscle fatigue [9, 10]. Previous studies reported that more than 10 years of farming experience or exceeding 6 working hours per day are associated with LE MSDs in farmers [3]. An earlier study from our group also found years of farming experience to correlate with malalignments of knee valgus and foot pronation in rice farmers [1].

Previous research indicated LE MSDs to be influenced by certain demographical characteristics, including gender, age and body mass index (BMI) [3 , 13]. Females were found to be more frequently associated with LE MSDs [16, 17] due to lower pain thresholds and physical tolerance, as compared with males [18]. It has been reported that a high BMI constitutes risk factor for LE MSDs, particularly knee pain in overweight individuals (BMI ≥25 kg/m²) [16, 17]. Weight increase in individuals increases lower limb joint loadings, which, in turn, may result in leg injury. Older individuals were reported to exhibit a higher rate of LE MSDs due to progressive joint degeneration and ligament laxity, as well as a decrease in physical performance [19]. Adults aged 40 years and older were found to show positive correlation with hip and foot MSDs [12, 17, 20].

Epidemiological studies concerning the prevalence of LE pain among rice farmers have already been reported [2]; however, a thorough investigation of LE pain and associated risk factors for each rice cultivation stage has not yet been conducted to the best of our knowledge. Related to this, most epidemiological studies identified risk factors based on the survey of incident rates, with less focus on risks due to the nature of specific job requirements (e.g., [1, 3]). Although a previous study [22] utilized expert evaluation of potential MSD risks for farmers based on systematic ergonomic assessment, the association of ergonomic risk factors with farmer discomfort had not been taken into consideration. The purpose of this study was to investigate LE pain perception and identify the associated factors for every stage of the rice cultivation process. The present study also applied expert risk assessment in conjunction with survey information as the basis for risk factor identification for LE pain. It was hypothesized that, albeit showing similar trends, pain perception and risk assessment scores would be different among individual cultivation stages due to the differences in nature of task performance. It is also expected that demographic and work-related risk factors would be positively associated with LE pain perception among rice farmers. Precise risk factor characterization of specific domains for each individual stage of the rice cultivation process could greatly benefit the development of effective intervention strategies or corrective guidelines focused on reducing these specific risk factors for particular populations during high-risk priority task performance.

2 Methods

2.1 Participants

Male and female farmers residing in Khon Kaen province, Thailand, aged 20–59 years and with at least one year of experience in every stage of the rice cultivation process, were recruited for the study. All participants were required to primarily work as rice farmers, with no secondary occupation, to provide a homogeneous sample and to exclude any influence from other work. Participants were excluded from the study if they experienced chronic hip, knee, ankle or foot pain within two weeks prior to the study. Incidence of chronic pain was assumed if participants reported gouty arthritis, rheumatoid arthritis, or ankylosing spondylitis, and/or a pain rating of more than 4 on a 0–10 scale [23]. The list of potential study participants working in the rice farming industry was generated from the database of the Khon Kaen Province Agricultural Extension Office. Participants were recruited using a multi-stage random sampling procedure. In this procedure, cluster sampling was initially applied to randomly select one district from a total of 18 districts, followed by simple random sampling to select 30 participants for the study.

2.2 Study procedure

The study was conducted to cover one complete cycle of the rice cultivation process (approximately 8 months). Prior to the study, participants read and signed an inform consent form approved by the Human Ethics Committee of Khon Kaen University (HE562079). Figure 2 presents the overall study and analytical procedure used in this study. A set of survey questionnaires was used to collect farmers’ information and pain perception ratings. Expert evaluations of task analysis and ergonomic risk assessment were conducted to specify risks due to the nature of the job requirements. A series of statistical analyses was then conducted to identify factors associated with LE pain. Each of these steps is described in detail in the following subsections.

Fig.2

Overall study and analytical procedure.

2.2.1 Survey of farmer information and pain perception

Participants were initially asked to provide demographic and work-related information, including age, gender, height, weight, number of years of farming experience and number of work hours per day, using a self-administered questionnaire. Prior to performing the first stage of the rice cultivation cycle, initial pain perception of hip, knee and foot was rated by each participant using a body chart of the hip, knee and ankle and foot region modified from the Standardized Nordic Questionnaire (SNQ) in Thai [24]. Pain rating scales ranged from 0 to 10 points, where 0 represented no pain and 10 signified intolerable pain. Participants were then instructed to perform normal rice cultivation activities for the number of work hours per day they previously indicated in the survey, throughout the course of the study. At the end of a workday during the latter part of each cultivation stage, participants were asked to rate their LE pain experienced during performance of normal cultivation activities in each specific stage. Although all reported ratings were considered to represent pain levels induced primarily by task performance in the cultivation stage of interest, a possible influence of carryover pain from prior stages on pain perception levels may not be completely ruled out. Perception of LE pain for each cultivation stage was calculated by subtracting the score rated at the end of the cultivation stage with the score rated prior to starting the cycle of rice cultivation.

2.2.2 Task analysis and ergonomic risk assessment

During task performance in each stage of the rice cultivation, direct and video-based observation were used to record anterior, lateral and posterior views of the farmer’s motions. A hierarchical task analysis (HTA; [25]) was generated based on the field observations and video analysis. The analysis involved identifying goals, plans and tasks. Each task included a sequence of operations and environmental and/or equipment conditions inducing performance of specific methods for individual tasks. The rice cultivation process was divided into 5 main tasks in accordance to the cultivation stage. Subtasks were then identified based on the requirements to accomplish the goal of each cultivation stage.

Subsequently, an ergonomic risk analysis was conducted independently by three expert analysts (ergonomists and physiotherapists) who had been trained and had at least three years of experience with this tool. The level of inter-observer agreement among three expert analysts was excellent (kappa = 0.996). The ergonomic risk evaluation method was based on the Industrial Ergonomics Screening Tool developed by the Ergonomics Center of North Carolina. The tool was developed based on the Rapid Upper Limb Assessment (RULA) methodology [26] with an extension to cover whole body parts. Measurement involved systematic screening methods based on exposure to repetitive motion, extreme force and awkward posture. The tool had been tested in our previous study [21] as well as in several other studies with respect to non-agricultural work. A rating scale ranging from 0 to 10 was used to evaluate each part. A rating score of 0–3 represented low risk priority, scores >3 and < = 6 indicated moderate risk priority, and a score >6 signified high risk priority. The aggregate risk level across all risk factors ranged from 0 to 30 based on the average of analyst risk priorities across LE parts for each task. The cut-off value of the job risk priority level was defined based on the priority matrix (similar to job risk assessment commonly used in safety research) presented in the Industrial Ergonomics Screening Tool. A two-stage risk assessment was conducted using the same screening tool by the same group of expert analysts. The first stage included an ergonomic risk evaluation for each subtask for all cultivation stages. The activity of interest was selected based on the ‘worst case’ scenario, which involved the most extreme postures, forces and repetitive motions in each subtask. The subtask, rated as the highest risk for each cultivation stage, was selected as a representative of the corresponding stage. Subsequently, the second stage of risk assessment was conducted based on the representative subtask of each cultivation stage. The assessment was applied individually as the risk exposure levels varied among farmers due to individual differences in anthropometry and movement strategy.

2.2.3 Statistical analyses of factors associated with LE pain

Statistical analyses were conducted to identify relationships between hip, knee, and ankle and foot pain (as the response variables) and demographic and work-related risk factors. Demographic factors included gender, age and BMI. Work-related factors referred to stage of cultivation, number of work hours per day, number of years of farming experience, and overall ergonomic risk scores. All analyses were conducted using the STATA program version 10 (STATA, college station, TX) based on a significance level of α= 0.05. Due to high correlation of pain perception among LE parts (r = 0.22–0.47, p < 0.0001), Multivariate Analysis of Variance (MANOVA) was initially conducted to identify any significant effects of risk factors across all response variables. Any insignificant factors were removed from subsequent statistical models. Regarding the significant cultivation stage, ANOVA was conducted to investigate which stage posed the highest pain, as well as overall risk score. Subsequent multiple linear regression analyses were performed separately for each cultivation stage to examine associated factors of pain perception for each LE part. Ergonomic risk scores were analysed separately to pinpoint whether LE pain resulted from improper motion, force, and/or posture performance.

3 Results and discussion

3.1 Descriptive statistics

3.1.1 Demographic data of participants

The descriptive statistics of the demographic characteristics of the participating farmers in this study are presented in Table 1. Participants included 17 female and 13 male rice farmers with an age ranging from 34 to 59 years and having BMIs ranging from 16.53 to 32.41 kg/m². Most farmers (76.7%) showed BMIs within the normal range (<25 kg/m²). The participants had been working in the rice cultivation industry for 3 to 40 years, on average 7.5 hours per day in the field with a range of work hours of 5–10 hours/day.

Table 1
Demographic characteristics of participants

Demographic Number Mean SD

Gender

Female 17

Male 13

Age (years) 45.9 6.21

Height (cm) 159.5 6.32

Weight (kg) 59.1 9.81

BMI (kg/m²) 23.2 3.73

Work hours (hr/day) 7.5 1.82

Experience (years) 26.9 9.98

Demographic	Number	Mean	SD
Gender
Female	17
Male	13
Age (years)		45.9	6.21
Height (cm)		159.5	6.32
Weight (kg)		59.1	9.81
BMI (kg/m²)		23.2	3.73
Work hours (hr/day)		7.5	1.82
Experience (years)		26.9	9.98

3.1.2 Ergonomic risk assessment

Based on the HTA, the subtasks for each cultivation stage were identified. Table 2 shows the highest-risk subtasks as a representative of the cultivation stage and associated ratings based on the first-stage “worst case” risk assessment. Details of the other subtasks and associated ratings are not presented here. The latter part of Table 2 displays the results of the second-stage risk assessment for each participant, based on the selected highest-risk subtask. In general, all stages of the rice cultivation activity posed a high risk potential for LE MSDs. Similar to the results of a previous study, high ergonomic risk due to awkward posture was observed for every cultivation stage [22]. The average risk scores based on the assessment of 30 farmers exhibited the same trend as the ratings for the most extreme posture, force and motion performance.

Table 2
Ergonomic risk assessment of LE MSDs injury for each cultivation stage

Cultivation stage Highest-risk subtask First-stage risk assessment Worst-case risk score (mean (SD)) Second-stage risk assessment average risk score (mean (SD))

Motion Force Posture Total Motion Force Posture Total

Plowing Straight plow 7.3 (0.5) 7.7 (0.5) 7.7 (0.5) 22.7 (1.2)(H) 7.1 (0.4) 7.5 (0.5) 7.2 (0.4) 21.8 (0.8)

Seeding Transfer seeds 5.0 (0.6) 6.7 (0.5) 7.9 (0.8) 19.6 (0.8)(H) 4.2 (0.4) 6.1 (0.3) 6.9 (0.5) 17.2 (0.8)

Planting Plant sprouts 7.5 (0.5) 7.8 (0.8) 8.9 (0.4) 24.2 (1.2)(H) 7.3 (0.5) 7.2 (0.4) 8.0 (0.5) 22.5 (0.9)

Fertilization Transfer fertilizer 5.0 (0.0) 6.2 (0.8) 7.9 (0.9) 19.1 (0.6)(H) 4.6 (0.5) 5.9 (0.3) 6.8 (0.5) 17.3 (1.0)

Harvesting Harvest crop 5.4 (0.5) 5.9 (0.4) 7.0 (0.9) 18.3 (1.3)(H) 4.6 (0.5) 5.4 (0.5) 6.5 (0.5) 16.5 (0.9)

Cultivation stage	Highest-risk subtask	First-stage risk assessment Worst-case risk score (mean (SD))	Second-stage risk assessment average risk score (mean (SD))
Plowing	Straight plow	7.3 (0.5)	7.7 (0.5)	7.7 (0.5)	22.7 (1.2)(H)	7.1 (0.4)	7.5 (0.5)	7.2 (0.4)	21.8 (0.8)
Seeding	Transfer seeds	5.0 (0.6)	6.7 (0.5)	7.9 (0.8)	19.6 (0.8)(H)	4.2 (0.4)	6.1 (0.3)	6.9 (0.5)	17.2 (0.8)
Planting	Plant sprouts	7.5 (0.5)	7.8 (0.8)	8.9 (0.4)	24.2 (1.2)(H)	7.3 (0.5)	7.2 (0.4)	8.0 (0.5)	22.5 (0.9)
Fertilization	Transfer fertilizer	5.0 (0.0)	6.2 (0.8)	7.9 (0.9)	19.1 (0.6)(H)	4.6 (0.5)	5.9 (0.3)	6.8 (0.5)	17.3 (1.0)
Harvesting	Harvest crop	5.4 (0.5)	5.9 (0.4)	7.0 (0.9)	18.3 (1.3)(H)	4.6 (0.5)	5.4 (0.5)	6.5 (0.5)	16.5 (0.9)

Note: Abbreviations H = high ergonomic risk level.

3.1.3 Pain perception

LE pain rating in the complete rice cultivation process is shown in Table 3. Descriptive data showed that, on average, the planting task performance induced the highest pain ratings for every part of the LE. In general, rice farmers perceived the highest pain in the hip, followed by knee and ankle and foot pain, respectively. These results are in agreement with previous findings [3] for Thai farmers indicating higher prevalence in hip and knee pain (41.16% and 35.4%, respectively) as compared with foot pain (10.29%).

Table 3
Descriptive statistics of LE pain rating increase with respect to ratings obtained prior to starting the rice cultivation cycle (numbers in parentheses denote standard deviations)

Cultivation stages Pain perception ratings

Hip pain (mean (SD)) Knee pain (mean (SD)) Ankle and foot pain (mean (SD))

Plowing 2.8 (2.07) 1.7 (1.70) 0.2 (0.15)

Seeding 4.5 (2.50) 2.7 (2.69) 0.4 (0.23)

Planting 5.9 (2.72) 4.7 (3.10) 1.1 (0.42)

Nursing and fertilization 0.5 (0.33) 0.2 (0.13) 0.05 (0.02)

Harvesting 4.4 (0.80) 2.7 (1.95) 0.5 (0.27)

Cultivation stages	Pain perception ratings
Plowing	2.8 (2.07)	1.7 (1.70)	0.2 (0.15)
Seeding	4.5 (2.50)	2.7 (2.69)	0.4 (0.23)
Planting	5.9 (2.72)	4.7 (3.10)	1.1 (0.42)
Nursing and fertilization	0.5 (0.33)	0.2 (0.13)	0.05 (0.02)
Harvesting	4.4 (0.80)	2.7 (1.95)	0.5 (0.27)

3.2 Results of factors associated with LE pain

3.2.1 Factors associated with overall LE pain

Significant effects of all work-related risk factors, including cultivation stage (p < 0.0001), daily work hours (p = 0.008), years of farming experience (p = 0.029) and ergonomic risk scores (p = 0.0001) were found on the family of response measures of hip, knee, and ankle and foot pain. The results confirmed that the performance of farming activities induced LE pain perception for rice farmers. For individual cultivation stages, different work requirements, including equipment use, environmental conditions, and tasks to complete, would lead to different pain levels in LE. Significant effects of the number of working hours, years of experience and risk scores were observed, conforming previous reports of agricultural studies [3 , 10–14]. As these factors were rated independently for each individual farmer, it is suggested that pain perception was induced by individual exposure levels to work-related risks.

Regarding demographic factors, the farmer’s age found to be associated with LE pain (p = 0.006). These observations were in accordance with previous studies revealing older persons to have a high risk for LE MSDs [12 , 20]. However, gender and BMI had no significant effect on LE pain perception (p > 0.05). Although female gender was reported as a risk factor for LE MSDs [16, 17], prior investigations on specific populations of Thai rice farmers found that females were more likely to demonstrate abnormal quadriceps (Q) angle, tibialfemoral angle and genu recurvatum, as compared with male farmers [1]. These abnormalities are associated with knee valcum, varus or hyperextension, which result in knee pain [27 –29]. Taking the correlation of pain perception among LE parts into account, overall pain might not be affected by the difference in gender. With regard to the BMI factor, previous studies reported overweight individuals to exhibit LE malalignment and MSDs [1 , 17]. However, most participants in this study had BMIs within the normal range; and therefore, might not demonstrate strong associations with pain perception. Based on these findings, insignificant factors, including gender and BMI, were removed from the subsequent statistical analyses.

3.2.2 Effects of cultivation stage on pain perception and risk assessment

Variations in work requirement are assumed to induce different pain and risk levels among the respective cultivation stages. Results revealed that the cultivation stage had significant effect on hip pain (p < 0.0001), knee pain (p < 0.0001) and foot pain (p = 0.027), as well as on the overall risk ratings (p < 0.0001). Post-hoc results for all ratings are summarized in Fig. 3. In accordance with the hypothesis, farmer pain perception and risk level of farming activity were different among the individual cultivation stages. A similar trend was also found for pain and risk rating.

Fig.3

Post-hoc results of effects of cultivation on: a) LE pain and; b) risk assessment. (For each rating, means with the same letter are not significantly different at alpha = 0.05).

The planting stage was found to pose the highest ergonomic risk level as well as to induce the highest pain perception. Planting activities in this stage involved repetitive, awkward postures of knee bending and stooping with twisting, while carrying heavy rice sprout bundles. Such working conditions may lead to an increased risk of repetitive strain injuries of the LEs and may also increase lower limb MSDs [9 , 31].

Nursing and fertilization activities generally induced low pain perception by farmers, as well as low risk ratings. Although the posture is similar to the seeding process, the nursing stage required less force due to carrying a dry fertilizer basket instead of a heavier basket containing the wet seeds. Moreover, farmers usually perform the nursing task in a slower walking pace, since they have to be careful not to step on the rice sprouts growing in the field. Less force and slower motion requirements thus lead to lower risk exposure and lower discomfort [9].

3.2.3 Factors associated with specific LE pain for each cultivation stage

For each cultivation stage, the collected results revealed that hip pain could not be modelled by a linear function. Knee and foot pain also did not establish a linear relationship with demographic and work-related risk factors during plowing and nursing processes. In general, the R-squared values for these regression models were relatively low (R² < 0.3, p > 0.05). It is possible that a non-linear relationship exists between pain perception and risk factors. Such a relationship might be approximated with greater precision by a non-linear modelling approach. Therefore, further assessment of the non-linear relationship of pain and the respective cultivation stages should be subject of more detailed investigation in future studies.

The results of significantly associated factors of pain perception (see Table 4) were generally found in line with our expectation. Expert assessment of risk, in terms of motion, force and posture, were positively associated with knee and foot pain for planting, seeding and harvesting stages. Similar to the results of a study covering small-scale agriculture [12], the age factor was also positively associated with foot pain for planting and harvesting stages. However, the number of years of farming experience surprisingly showed negative association with foot pain for planting and harvesting stages, clearly contradicting earlier reports [1, 3]. This might be traced back to the differences in terms of exertion and fatigue potential based on levels of expertise in rice farming task performance and equipment use. Studies on sports and other occupational work have found that, as compared with novices, experts develop safer and more efficient movement strategies [32 –34], and experience less fatigue [35, 36]. In the context of agricultural work performance, we previously compared experienced and novice rice farmers in terms of grip force and arm muscle activity during plowing task execution [37]. The results of this study revealed experienced farmers to be capable of utilizing their arms more effectively than untrained participants and adopting balanced activity levels for agonist and antagonist arm muscles. In analogy, rice farmers with higher working experience might also be able to develop similarly effective movement strategies for LE movement during the planting and harvesting process. Thus, future research should emphasize on the investigation of peculiar LE movement strategies of experienced rice farmers during these stages in order to facilitate the development of training protocols for effective muscle use and LE pain risk minimization in the rice cultivation process.

Table 4
Results of factors associated with LE pain for each cultivation stage

Pain: Cultivation Stage Age Work hour Experience Motion Force Posture

Knee pain

Seeding

Coefficient 0.09 –0.37 –0.004 0.10 4.62 –1.19

t 0.81 –1.36 –0.06 0.08 2.8 –1.02

p 0.423 0.187 0.956 0.934 0.010^* 0.318

Planting

Coefficient 0.005 –0.54 –0.02 2.66 0.61 2.84

t 0.05 –1.96 –0.24 2.58 0.49 2.9

p 0.964 0.062 0.813 0.017^* 0.627 0.008^*

Harvesting

Coefficient –0.05 –0.31 0.05 1.77 2.16 –0.26

t –0.59 –1.48 0.94 2.41 2.86 –0.3

p 0.563 0.159 0.365 0.029^* 0.012^* 0.766

Foot and ankle pain

Planting

Coefficient 0.22 –0.02 –0.11 0.33 2.52 0.36

t 2.75 –0.09 –2.24 0.42 2.67 0.48

p 0.011^* 0.929 0.035^* 0.682 0.014^* 0.637

Harvesting

Coefficient 0.13 –0.03 –0.10 –0.55 0.29 0.35

t 2.48 –0.2 –3.09 –1.12 0.59 0.62

p 0.026^* 0.8426 0.007^* 0.281 0.566 0.545

Pain: Cultivation Stage	Age	Work hour	Experience	Motion	Force	Posture
Knee pain
Seeding
Coefficient	0.09	–0.37	–0.004	0.10	4.62	–1.19
t	0.81	–1.36	–0.06	0.08	2.8	–1.02
p	0.423	0.187	0.956	0.934	0.010^*	0.318
Planting
Coefficient	0.005	–0.54	–0.02	2.66	0.61	2.84
t	0.05	–1.96	–0.24	2.58	0.49	2.9
p	0.964	0.062	0.813	0.017^*	0.627	0.008^*
Harvesting
Coefficient	–0.05	–0.31	0.05	1.77	2.16	–0.26
t	–0.59	–1.48	0.94	2.41	2.86	–0.3
p	0.563	0.159	0.365	0.029^*	0.012^*	0.766
Foot and ankle pain
Planting
Coefficient	0.22	–0.02	–0.11	0.33	2.52	0.36
t	2.75	–0.09	–2.24	0.42	2.67	0.48
p	0.011^*	0.929	0.035^*	0.682	0.014^*	0.637
Harvesting
Coefficient	0.13	–0.03	–0.10	–0.55	0.29	0.35
t	2.48	–0.2	–3.09	–1.12	0.59	0.62
p	0.026^*	0.8426	0.007^*	0.281	0.566	0.545

Note: ^*Indicated significant at alpha = 0.05 level.

The collected results of the present study also revealed that the magnitude of effect of the risk factors varies significantly within the different cultivation stages (see Table 4). Comparing with effects of age and years of experience, ergonomic factors of motion, force and posture had greater influence on pain perception. Perception of LE pain was estimated to increase by 1.8–4.6 times when the ratings of ergonomic factors increased by 1 score point. The force factor was found to be a significant effector of knee pain during seeding task performance. The seeding process requires force exertion by lifting and carrying a heavy sack and basket of wet rice seeds (weight more than 10 kg), which might overload knee muscles and tendons [9, 19]. For the planting process, motion and posture factors were found to effect knee pain perception significantly. This result was in line with observations from a previous study [15], indicating the extended repetition (> = 6 hours/day) of stooping together with a twisting posture, as typically performed during the planting process, to be a risk factor for knee musculoskeletal impairment in rice farmers. The force factor was further found to be a significant effector of foot pain during the planting task. Performing planting work involving repetitive trunk stooping and twisting, while carrying heavy load on a muddy walking surface created excessive loading on trunk and foot muscles [9]. The muddy environment condition would also increase the instability of ankle and foot and represent a challenge for controlling body alignment [38]. In the harvesting stage, force and motion factors were found to significantly affect knee pain perception. The harvesting activities involve repetitive stooping with trunk twisting, which is somewhat similar to, although not as extreme as, the posture and motion performed during the planting process. In addition, farmers typically performed forceful cutting of several stems of crop using a sickle and carried a heavy bundle of crops before resting it on the ground. The high force exertion levels associated with this procedure generated a high load on LE muscles and tendons and might increase the risk of knee injury and discomfort [9, 12, 13, 19].

4 Conclusion

The present study aimed to identify factors associated with LE pain for each stage in the cultivation cycle. The planting stage was found to pose the highest ergonomic risk level as well as to induce the highest LE pain. The findings showed ergonomic factors (i.e., improper motion, force and posture) to exert the most substantial influence on pain perception. In terms of demographic factors, the older participants were associated with greater foot pain perception. Another interesting finding was that years of farming experience unexpectedly showed negative association with foot pain. We suspect that more experienced farmers might develop more effective muscle usage and movement strategies for the LEs during these stages, as compared with less experienced farmers. The findings suggested that further development of intervention strategies and guidelines for rice farmers should focus on reducing forceful muscular exertion, awkward posture as well as repetitive motion during the planting process, particularly for older farmers, to minimize the risk of foot pain. Future research should also be directed at objectively investigating the LE movement strategy of experienced rice farmers using muscle activity and gait analysis. The implications of this research are anticipated to benefit the development of supplementary guidelines and training programs for less experienced and novice farmers.

However, the fact that a linear relationship among LE pain perception, demographic factors and work-related factors was assumed represents a limitation of this work. The linear model, as evident from relatively low R-squared values for the regression models, might only represent a crude approximation of the complex relationship between these factors. Thus, the application of novel algorithms, for example machine learning approaches, should be investigated in the future in order to eliminate linear relationship assumptions between pain perception and risk factors.

Conflict of interest

None to report.

Footnotes

Acknowledgments

This study was primary supported by grants from Thailand Research Fund (TRF), Office of the Higher Education Commission (OHEC) and Khon Kaen University (No. MRG5680009). The opinions expressed in this paper are those of the authors and do not necessarily reflect the views of TRF, OHEC or Khon Kaen University.

References

Karukunchit

, Puntumetakul

, Swangnetr

, Boucaut

. Prevalence and risk factor analysis of lower extremity abnormal alignment characteristics among rice farmers. Patient Preference and Adherence 2015;9:785–95.

Puntumetakul

, Siritaratiwat

, Boonprakob

, Eungpinichpong

, Puntumetakul

. Prevalence of musculoskeletal disorders in farmers: Case study in Sila, Muang Khon Kaen, Khon Kaen province. Journal of Medical Technology and Physical Therapy 2011;23(3):297–303.

Osborne

, Blake

, Fullen

, Meredith

, Phelan

, McNamara

, Cunningham

. Risk factors for musculoskeletal disorders among farm owners and farm workers: A systematic review. American Journal of Industrial Medicine 2012;55(4):376–89.

Woolf

, Pfleger

. Burden of major musculoskeletal conditions. Bulletin of the World Health Organization 2003;81(9):646–56.

Mokkamul

. Ethnobotanical Study of Rice Growing Process in Northeastern, Thailand. Ethnobotany Research and Applications 2006;4:213–22.

da Costa

, Vieira

. Risk factors for work-related musculoskeletal disorders: A systematic review of recent longitudinal studies. American Journal of Industrial Medicine 2010;53(3):285–323.

, Lu

, Gu

, Zhou

, He

, Wang

. Musculoskeletal symptoms and associated risk factors in a large sample of Chinese workers in Henan province of China. American Journal of Industrial Medicine 2012;55(3):281–93.

Vignon

, Valat

, Rossignol

, Avouac

, Rozenberg

, Thoumie

, Avouac

, Nordin

, Hilliquin

. Osteoarthritis of the knee and hip and activity: A systematic international review and synthesis (OASIS). Joint Bone Spine 2006;73(4):442–55.

Reid

, Bush

, Karwowski

, Durrani

. Occupational postural activity and lower extremity discomfort: A review. International Journal of Industrial Ergonomics 2010;40(3):247–56.

10.

Meyer

, Radwin

. Comparison of stoop versus prone postures for a simulated agricultural harvesting task. Applied Ergonomics 2007;38(5):549–55.

11.

Walker-Bone

, Palmer

. Musculoskeletal disorders in farmers and farm workers. Occupational Medicine 2002;52(8):441–50.

12.

Naidoo

, Kromhout

, London

, Naidoo

, Burdorf

. Musculoskeletal pain in women working in small-scale agriculture in South Africa. American Journal of Industrial Medicine 2009;52(3):202–9.

13.

Davis

, Kotowski

. Understanding the ergonomic risk for musculoskeletal disorders in the United States agricultural sector. American Journal of Industrial Medicine 2007;50(7):501–11.

14.

Xiao

, McCurdy

, Stoecklin-Marois

, Li

, Schenker

. Agricultural work and chronic musculoskeletal pain among Latino farm workers: The MICASA study. American Journal of Industrial Medicine 2013;56(2):216–25.

15.

Karukunchit

. Physical ergonomics risk factor analyses of lower extremity impairments in rice cultivation [dissertation]. [Khon Kaen (TH)]: Khon Kaen University; 2015.

16.

Holmberg

, Thelin

, Stiernström

, Svärdsudd

. The impact of physical work exposure on musculoskeletal symptoms among farmers and rural non-farmers: A population-based study. Annals of Agricultural and Environmental Medicine 2003;10(2):179–84.

17.

Fransen

, Agaliotis

, Bridgett

, Mackey

. Hip and knee pain: Role of occupational factors. Best Practice & Research Clinical Rheumatology 2011;25(1):81–101.

18.

Keogh

, Herdenfeldt

. Gender, coping and the perception of pain. Pain 2002;97(3):195–201.

19.

Messing

, Tissot

, Stock

. Distal lower-extremity pain and work postures in the Quebec population. American Journal of Public Health 2008;98(4):705–13.

20.

Sprince

, Park

, Zwerling

, Whitten

, Lynch

, Burmeister

, Thu

, Gillette

, Alavanja

. Risk factors for low back injury among farmers in Iowa: A case-control study nested in the agricultural health study. Journal of Occupational and Environmental Hygiene 2007;4(1):10–6.

21.

Swangnetr

, Kaber

, Puntumetakul

, Gross

. Ergonomics-related risk identification and pain analysis for farmers involved in rice field preparation. Work 2014;49(1):63–71.

22.

Kotowski

, Davis

, Kim

, Lee

. Identifying risk factors of musculoskeletal disorders on Korean farms. Work 2014;49(1):15–23.

23.

Jensen

, Chen

, Brugger

. Interpretation of visual analog scale ratings and change scores: A reanalysis of two clinical trials of postoperative pain. The Journal of Pain 2003;4(7):407–14.

24.

Saetan

, Khiewyoo

, Jones

, Ayuwat

. Musculoskeletal disorders among northeastern construction workers with temporary migration. Srinagarind Medical Journal (SMJ) 2010;22(2):165–73.

25.

Diaper

, Stanton

, editors. The handbook of task analysis for human-computer interaction. CRC Press; 2003.

26.

McAtamney

, Corlett

. RULA: A survey method for the investigation of work-related upper limb disorders. Applied Ergonomics 1993;24(2):91–9.

27.

Solberg

, Gur

, Adar

. Postural disorders and musculoskeletal dysfunction: Diagnosis, prevention and treatment. Elsevier Health Sciences 2007.

28.

Devan

, Pescatello

, Faghri

, Anderson

. A prospective study of overuse knee injuries among female athletes with muscle imbalances and structural abnormalities. Journal of Athletic Training 2004;39(3):263.

29.

Magee

. Orthopedic physical assessment. Elsevier Health Sciences 2014.

30.

Allen

, Chen

, Callahan

, Golightly

, Helmick

, Renner

, Jordan

. Associations of occupational tasks with knee and hip osteoarthritis: The Johnston County Osteoarthritis Project. The Journal of Rheumatology 2010;37(4):842–50.

31.

McWilliams

, Leeb

, Muthuri

, Doherty

, Zhang

. Occupational risk factors for osteoarthritis of the knee: A meta-analysis. Osteoarthritis and Cartilage 2011;19(7):829–39.

32.

Ganon

, Plamondon

, Gravel

, Lortie

. Knee movement strategies differentiate expert from novice workers in asymmetrical manual materials handling. Journal of Biomechanics 1996;29(11):1445–53.

33.

Plamondon

, Denis

, Delisle

, Larivière

, Salazar

, IRSST MMH research group. Biomechanical differences between expert and novice workers in a manual material handling task. Ergonomics 2010;53(10):1239–53.

34.

Chen

, Lee

, Chen

. Differences in lifting strength profiles between experienced workers and novices at various exertion heights. International Journal of Industrial Ergonomics 2011;41(1):53–8.

35.

Maisetti

, Boyas

, Guevel

. Specific neuromuscular responses of high skilled laser sailors during a multi-joint posture sustained until exhaustion. International Journal of Sports Medicine 2006;27(12):968–75.

36.

Boyas

, Maisetti

, Guevel

. Changes in sEMG parameters among trunk and thigh muscles during a fatiguing bilateral isometric multi-joint task in trained and untrained subjects. Journal of Electromyography and Kinesiology 2009;19(2):259–68.

37.

Swangnetr

, Kaber

. Analysis of novice and experienced rice farmer grip force and arm muscle activity in a plowing task. Advances in Physical Ergonomics and Human Factors: Part II 2014;15:49.

38.

Donatelli

, Wooden

. Orthopaedic physical therapy. Elsevier Health Sciences 2009.

Cultivation stages	Pain perception ratings
	Hip pain (mean (SD))	Knee pain (mean (SD))	Ankle and foot pain (mean (SD))
Plowing	2.8 (2.07)	1.7 (1.70)	0.2 (0.15)
Seeding	4.5 (2.50)	2.7 (2.69)	0.4 (0.23)
Planting	5.9 (2.72)	4.7 (3.10)	1.1 (0.42)
Nursing and fertilization	0.5 (0.33)	0.2 (0.13)	0.05 (0.02)
Harvesting	4.4 (0.80)	2.7 (1.95)	0.5 (0.27)

Identification of influential demographic and work-related risk factors associated to lower extremity pain perception among rice farmers

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1 Introduction

2.1 Participants

2.2 Study procedure

2.2.2 Task analysis and ergonomic risk assessment

2.2.3 Statistical analyses of factors associated with LE pain

3 Results and discussion

3.1 Descriptive statistics

3.1.1 Demographic data of participants

Table 1 Demographic characteristics of participants Demographic Number Mean SD Gender Female 17 Male 13 Age (years) 45.9 6.21 Height (cm) 159.5 6.32 Weight (kg) 59.1 9.81 BMI (kg/m2) 23.2 3.73 Work hours (hr/day) 7.5 1.82 Experience (years) 26.9 9.98

3.2.1 Factors associated with overall LE pain

3.2.2 Effects of cultivation stage on pain perception and risk assessment

Conflict of interest

Footnotes

Acknowledgments

References

Table 1
Demographic characteristics of participants

Demographic Number Mean SD

Gender

Female 17

Male 13

Age (years) 45.9 6.21

Height (cm) 159.5 6.32

Weight (kg) 59.1 9.81

BMI (kg/m²) 23.2 3.73

Work hours (hr/day) 7.5 1.82

Experience (years) 26.9 9.98