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ISSN : 1598-7248 (Print)
ISSN : 2234-6473 (Online)
Industrial Engineering & Management Systems Vol.18 No.4 pp.710-718

Participatory Ergonomic Approach Impacted on Functions in Knee Osteoarthritis: Clustered Randomized Controlled Trial

Napaporn Tangadulrat*, Pornit Wattanapisitkul, Tippawan Kaewmanee, Sangarun Isaramalai, Kanokwan Hounsri, Varah Yuenyongviwat, Chanon Kongkamol
Department of Physical Therapy, Faculty of Medicine, Prince of Songkla University, Songkhla, Thailand
Research Center for Caring System of Thai Elderly, Faculty of Nursing, Prince of Songkla University, Songkhla, Thailand
Department of Orthopaedic Surgery and Physical Medicine, Faculty of Medicine, Prince of Songkla University, Songkhla, Thailand
Research Unit of Holistic and Safety Management in Community, Prince of Songkla University, Songkhla Thailand
Corresponding Author, E-mail:
May 7, 2019 September 15, 2019 October 18, 2019


Knee osteoarthritis (KOA) is one of the most prevalent chronic conditions among aged para rubber farmers in Thailand. The sapping process causes ergonomic hazards leading to aggravating pain and functional disabilities. Muscle strengthening exercises, both non-weight-bearing exercise (NWE) and progressive resistance exercise (PRE), reduce those burdens. However, only muscle strengthening exercise may not be sufficient for the improvement of individual functional ability. Participatory ergonomic approaches (PEAs) were developed and implemented in this study. The objective of this study was to compare the performance-based results among the PRE-PEA, NWE-PEA, and standard treatment (STG) groups in aged para-rubber farmers with KOA. The participants performed self-practice for 8 weeks and recorded compliance daily. The primary outcomes that included the timed up and go test (TUG), 40-meter fast paced walk test (40mFPWT), and stair climb test (SCT) were measured at baseline, 5, and 9 weeks. The results showed that a mean comparison of the 3-paired groups resulted in statistically significant differences in TUG, 40mFPWT, and SCT between the PRE-PEA vs. STG and NWE-PEA vs. STG (p<0.001). PEAs with PRE and NWE could improve functional abilities in both the performance-based and patient-report assessments in aged para rubber farmers with KOA.



    Knee osteoarthritis (KOA) is a common chronic joint disorder in the elderly. In Thailand, aged para rubber farmers are significantly vulnerable to develop KOA (Teerachitkul et al., 2012). The main risk factor for increasing severity of KOA is an occupational mechanical loading of the knee joint (Palmer, 2012). KOA can lead to negative physical, mental, and economic impacts on aged workers such as pain, limited functional capacity, and loss of productivity (Palmer, 2012;Teerachitkul et al., 2012). Thus, enhancing functional improvement needs to be a concern in KOA.

    There are two possible causes of KOA among aged para rubber farmers: 1) physical load on the knee joint and 2) a lack of knee muscle endurance. Occupational activities such as repetitive squatting, kneeling, and heavy lifting which increase physical load on the knee joint in the sapping process are likely to contribute to disease occurrence and to symptom aggravation (McWilliams et al., 2011;Palmer, 2012). The other cause of KOA is inadequate strength of quadriceps muscles resulting in the inability to execute repeated contractions over a prolonged period causing functional performance impairment (Ikeda et al., 2005). Previous studies showed that most para rubber farmers lacked knowledge on occupational risk factors (Wongphon and Inmuong, 2012) and regular exercise (Teerachitkul et al., 2012). Consequently, proper working conditions and muscle strengthening exercise should be implemented in functional performance improvement among aged Thai para rubber farmers.

    A meta-analysis revealed that strengthening exercises can reduce pain and improve physical function. However, no significant difference was reported on various muscle strengthening exercises in improving physical function (Fransen et al., 2015). Non-weight-bearing exercise (NWE) is an exercise performed with the individual’s body weight and there is no need for any mechanical equipment (Jan et al., 2009). In contrast, progressive resistance exercise (PRE) is a method of increasing the ability of muscles to generate force by increasing the external resistance. However, merely strengthening the muscles through exercise may not exclusively improve individual functional ability (Bennell and Hinman, 2011).

    Participatory Ergonomic Approach (PEA) is evidenced as one of the effective strategies enhancing workers’ health outcomes (Hignett et al., 2005). The main concept of PEA is self-care behavioral promotion requiring strategies for enhancing ergonomic management and helping overcome barriers to change behaviors. PEA processes comprise raising risk factor awareness and attitudes towards ergonomic measures by problem solving approaches. Consequently, solution implementation will be carried out for enhancing abilities to change (Rivilis et al., 2008). The theory of self-care operations: estimative, transitional, and productive operations (Orem et al., 2001) were adopted to enhance the PEA processes. Contribution of workers is needed on planning and controlling their working conditions, with sufficient knowledge and power to influence on both processes and outcomes for achieving desirable goals (Hignett et al., 2005).

    Integrating PEA into an 8-week progressive resistance and non-weight-bearing strengthening exercise was designed to enhance functional improvement among aged Thai para rubber farmers with KOA. Therefore, this study aimed to compare the functional performances among PRE and PEA (PRE-PEA), NWE and PEA (NWE-PEA), and a standard treatment group (STG) in aged para rubber farmers with KOA.


    2.1 Study Design

    The study was a clustered randomized controlled trial in KOA patients from three community health promoting centers in Songkhla, Thailand from July 2015 to June 2016. The study was approved by the Institutional Review Board, Faculty of Medicine, Prince of Songkla University.

    2.2 Subjects and Eligibility

    The recruited subjects were Thai men and women aged ≥ 60 years. All were para rubber farmers with a symptomatic clinical diagnosis of chronic KOA defined as at least 2 symptoms of the following: joint stiffness less than 30 min, crepitus on active motion, bony tenderness, bony enlargement but no palpable warmth or synovial mass based on the criteria of the American College of Rheumatology (1986) and the Kellgren-Lawrence radiographic grading scale by X-ray computer less than 4. In addition, the subjects had no history of intra-articular injection of steroids or hyaluronic acid into either knee within past three months and no history of any knee trauma or surgery. However, use of stable doses of antiinflammatory drugs was allowed.

    The exclusion criteria were rheumatoid arthritis, having other causes of pain and history of surgery in lower limbs, contraindications for exercise (such as myocardial infarction, uncontrolled hypertension), and unable to complete the recruitment questionnaire. Discontinuation was allowed on individual request due to severe knee pain.

    2.3 Clustered Randomization Procedure

    A random allocation sequence was generated by the “ICE” package of the R program. The Cluster were randomized into one of three communities: PRE-PEA, NWE-PEA, and STG. The sample size was calculated based on our pilot study using command “lmmpower” in the “longpower” package of the R program which yielded a sample size of 25 participants in each group. Since we expected some aged workers would withdraw from the ergonomic management and strengthening exercise intervention, we added 20% to the number of participants to compensate for drop-outs. CK prepared the allocation sequence list and KH carried out the allocation with the volunteers by identifying their homes and working areas (Figure 1). Informed consent was obtained at the first visit. This was an open trial and by necessity the participants and those delivering the interventions were not blind to the allocation.

    2.4 Intervention

    During the first week, both treatment groups (i.e. PRE-PEA and NWE-PEA) participated in a series of health education sessions:

    • (1) A 20-minute group discussion to analyze job hazards. The discussion helped the participants identify current ergonomic risk factors that increase the severity of KOA in their work activities, such as low tapping, knife sharpening, and manual handling of the latex. In addition, their self-care capability was determined.

    • (2) A 60-minute health education session was conducted on the causes and effects of KOA, ergonomic management, such as improving working conditions, avoiding certain postures, and performing muscle strengthening exercises.

    • (3) A 40-minute hands-on demonstration of strengthening exercises based on individual assessments by physiotherapists.

    • (4) A 30-minute session was implemented on working conditions modified by the participants under the supervision of an ergonomist, physical therapists, and nurse practitioners. Their personal goals and action plans were also designed into the session.

    • (5) A 10-minute session was provided on guidance for compliance of recording the ergonomic management.

    After the first week, four 30-minute home visits were conducted every other week. They were carried out to encourage ergonomic management by the participants in their daily lives. Enhancing self-evaluation, re-setting goals and planning, and positive reinforcement were provided.

    The STG received usual care services based on standard protocols coupled with a 2-hour boosted educational session.

    All participants in both exercise programs were required to complete their own exercise programs at least 3 days per week for 8 weeks. Both exercise programs were designed to increase lower extremity muscle strength bilaterally around the hip and knee joints (Table 1 and Figure 2).

    The exercise sessions included at least 3 sets of 10 repetitions of 9 exercises. Each exercise started with dynamic movement through a full range of motion and continued to a 10-second hold static movement at the end range of movement. The repetitions and durations of exercises were prescribed by the participants with PEA.

    In the PRE group, the intensity was based on the ability of the participant to execute 10 repetitions maximum (10 RM). Sandbags were used for the weight increments starting from 50% of 10 RM in the first and second weeks and increased to 75% of 10 RM in the third and fourth weeks and reached 100% of 10 RM in the fifth through eighth weeks. The load adjustment took place under the supervision of an experienced physical therapist to yield a gradual progression of training.

    Additionally, both exercise groups received muscle strengthening training booklets. The NWE booklet explained 9 exercises of unweighted leg movements while the PRE booklet described 9 sandbag exercises. All exercise sessions were self-instructed and took place at home. Home visitations were conducted every two weeks by a physical therapist and nurse practitioner to check on compliance and exercise procedures.

    2.5 Instruments

    The Demographic and Health Information Form (DHFF) was developed by KH and consists of the general data, work characteristics, and health status of the participants.

    The functional performance tests comprised Timed Up and Go Test (TUG), 40m Fast Paced Walk Test (40mFPWT), and Stair Climb Test (SCT) which were recommended by Osteoarthritis Research Society International (OARSI) (Dobson et al., 2012;Dobson et al., 2013).

    Timed Up and Go Test (TUG) is a transition test of strength, agility and dynamic balance in ambulatory activity which incorporating multiple activity themes including a test of sit-to-stand activity, a test of walking short distances and a test of changing direction during walking, and the transitions between the activities. A test of taken to rise from a chair, walk 3 meters, turn, walk back to the chair, then sit down wearing regular footwear and using a walking aid if required. The 40m Fast Paced Walk Test (40mFPWT) is a test of short distance walking activity which including walking speed over short distances and changing direction during walking. A test that is timed over 4 x 10 meter for a total 40 meter. The Stair Climb Test (SCT) is a test of lower body strength and balance in ascending and descending stair activity. The time (in seconds) it takes to ascend and descend a flight of stairs. The number of stairs will depend on individual environmental situations. Where possible, the 9-step stair test with 20 centimeters step height and handrail is recommended (Dobson et al., 2012;Dobson et al., 2013).

    The DHFF was collected only in the first week, whereas the others were measured at baseline, the fifth week, and the ninth week.

    2.6 Data Analysis

    The data analyses were conducted with R version 3.2.5. The one-way ANOVA, Kruskal-Wallis, and Chi’s squared tests were used to compare the data of three randomized groups at baseline. Mean comparisons of TUG, 40mFPWT, and SCT between PRE-PEA vs. STG and NWE-PEA vs. STG with generalized linear mixed models (GLMM) using the “nlme” package and additional p-values were calculated based on Satterthwate’s approximations using the “lmerTest”. Stepwise regressions were conducted considering Akaike information criterion (AIC) or log-likelihood depended on their intraclass correlation of variances. The level of significance was set at 0.05 (two-tailed).

    3. RESULTS

    3.1 Participant Characteristics

    A total of 75 patients were assigned into either the PRE-PEA, NWE-PEA or STG group and completed the baseline examination. All 75 participants (58 females, 17 males) completed the 5-week and the 9-week follow-up examinations. Patients ranged in age from 60 to 77 years, with a mean ± SD age of 66.9 ± 4.5 years for NWE-PEA, 68.0 ± 5.8 years for PRE-PEA, and 63.7 ± 4.3 years for STG. The clinical characteristics of the participants were summarized in Table 2.

    3.2 Functional Performance Tests

    Results of all 3 functional performance tests are given in Table 3. The mean ± SD changes in the TUG score for the NWE-PEA and PRE-PEA scores from baseline to 9 weeks were 1.83 ± 1.80 sec and 1.75 ± 1.40 sec, respectively. The mean ± SD changes in the 40mFPWT score for the NWE-PEA and PRE-PEA from baseline to 9 weeks were 0.22 ± 0.13 sec and 0.21 ± 0.13 sec, respectively. The mean ± SD changes in the SCT score for the NWE-PEA and PRE-PEA from baseline to 9 weeks were 3.03 ± 2.66 sec and 3.32 ± 2.82 sec, respectively.

    3.3 Overall Functional Performance from Baseline to the 9-week Follow-up

    Results of all 3 functional performance tests are given in Figure 3. The pattern of mean and 95% confidence interval of all 3 functional performance from baseline to the 9-week follow-up were in the same fashion. For TUG and SCT, the mean of their values were decreaing after training. In the other hand, For 40mFPWT, the mean of their values were increaing after training. In STG, the mean of TUG, SCT and 40mFPWT were stand still over the study.

    According to the GLMM analyses, statistically significant differences were found between treatment groups overtime for all functional performance tests. The p-values of the TUG, 40mFPWT, and SCT outcomes between the NWE-PEA and STG were p = 0.02, p = 0.035, and p < 0.001, respectively. The p-values of the TUG, 40mFPWT, and SCT outcomes between the PRE-PEA and STG were p = 0.008, p = 0.021, and p < 0.001. The R2GLMM(c) were 0.66, 0.87, and 0.93 in the TUG, 40mFPWT, and SCT models, respectively (Table 4).


    The results from this study showed enhanced functional improvement using the PEA with PRE and NWE in aged Thai para rubber farmers with KOA. All 3 functional performance tests which are recommended from OARSI were as a batteries test of direct measures of strength, agility and dynamic balance by testing in the abilities to walk quickly over short distances, changing direction during walking, and the transitions between the activities, which are important but often limited in people with KOA (Dobson et al., 2013).

    The mechanism might be from NWE and PRE programs including isometric and dynamic exercises were designed mainly to increase strength and endurance in the quadriceps and hamstrings muscles. Power of the quadriceps muscles is imperative for osteoarthritic patients to improve knee joint stability, increase shock absorption, and diminish ground reaction forces during gait (Lim et al., 2008). Moreover, both programs can enhance muscle coordination between the quadriceps and hamstrings muscles. It was reported that quadriceps and hamstrings muscles provided dynamic frontal plane stability and supported abduction-adduction moments (Al-Johani et al., 2014). Adequate strength of the quadriceps and hamstrings muscles have the potential responsibility for incorporating activities of daily living and functional tasks such as gait and other weight bearing activities. In addition, these interventions comprised hip exercises in three directions: flexion, extension, and abduction during standing. Strengthening of hip muscles can increase pelvic stability and improve lower limb alignment and attenuate knee adduction moment during dynamic functional tasks (Lun et al., 2015).

    In the present study, both NWE and PRE training programs emphasized dynamic strengthening exercises of the quadriceps, hamstrings, and hip muscles in the range of motions associated with functional tasks in daily life. All participants worked as para rubber farmers that required endurance of the lower limb muscles and core stabilization associated with their job activities including level, uphill, and downhill walking. These activities contributed to muscle activities in terms of endurance rather than strength. Other PRE protocols were often more focused on muscle strength than muscle endurance. On the other hand, the intensity and duration of our exercise protocols for the NWE and PRE groups were modified for individual performance to particularly enhance double-leg muscle endurance.

    Our study outcomes were examined with functional performance tests that included the TUG, SCT, and 40mFPWT. These tests reflected the abilities of functional balance and speed during short distance walking and stair negotiation activity. Functional gait and stair ascending and descending activities required dynamic lower extremity muscular control that was not only concentric but also eccentric contraction to move through the range of motion for the hip (0°–30°), knee (0°–30°), and ankle (0°– 10°) (Topp et al., 2002). Thus, there were significant improvements in all variables in the PEA-NWE and PEAPRE over the 8-week intervention which were similar with the results of previous studies (Al-Johani et al., 2014;Lun et al., 2015;Topp et al., 2002). It could be explained that strengthening exercises helped to increase α-motor neuron activity influenced by Golgi tendon organs and muscle spindles within the trained muscles and this led to improved muscle tone. Consequently, strengthening exercise might absorb the impact loads through the knee joint with the mechanism of increasing muscle strength around the knee joint and increasing muscle coordination and proprioceptive sensitivity within the muscles and the knee joint during weight-bearing activities. Additionally, this might contribute to the enhanced ability of postural control and balance with the result of significant improvement in the TUG scores between the PEM-PRE and PEM-NWE groups.

    This study dealt with the clinically important changes reported by the outcome measures. It demonstrated meaningful changes in the TUG scores over the 8- week intervention with significant decreases: -1.83 in the NWE group and -1.75 in the PRE group. The minimally clinically important changes (MCIC) were more than 1.4 points over the 8-week period (Wright et al., 2011). Though the 40mFPWT showed statistically significant improvement in the NWE and PRE groups compared with the control group, unimportant clinical changes were found in both groups with changes of 0.21 and 0.22 m/s in the NWE and PRE groups, respectively, over the 8- week intervention. A MCIC would be more than 0.2 m/s (Wright et al., 2011).

    This program also focused on patient participation in a series of ergonomic health education sessions through group discussion which helped improve their understanding, and practicability which involved the patient as a collaborator and partner in the decision making to care (Haywood et al., 2006). A systematic review indicated the importance of PEA which increased risk awareness and attitudes towards ergonomic measures by problem solving approaches. Moreover, solution implementation from the process was carried out to enhance the abilities to positive health behaviours (Rivilis et al., 2008).


    Participatory ergonomic approaches with progressive resistance exercise and non-weight-bearing exercise improved the functional abilities in both performancebased and patient-report assessments in aged para rubber farmers with KOA.


    We were more grateful to thanks Assistant Professor Wipawan Leelasamran, Miss Watsaporn Suksom, and Miss Phakatip Cheunchoksan.



    Flow diagram of trial.


    Strengthening exercise. 2a: straight-leg raise; 2b: hip abduction; 2c: hip flexion; 2d: hip extension; 2e: knee flexion; 2f: knee flexion; 2g: hip extension; 2h: straight-leg raise; 2i: Quad set.


    Mean and 95% confidence interval of results of all 3 functional performance from baseline to the 9-week follow-up. TUG: Time Up and Go Test; 40mFPWT: 40m Fast Paced Walk Test; SCT: Stair Climb Test.


    Description of strengthening exercise (NWE and PRE) performed by intervention groups

    Participants characteristics at baseline (N=75)

    Functional Performance tests

    Fixed effects estimates in the generalized linear mixed model for functional performance tests from baseline to 9 weeks


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