AN EVALUATION OF PHYSIOLOGICAL STRAIN FROM LAWN MOWING

Pornsiri Jongkola,*, Noppachat Wiriyanukulb

a,bSchool of Industrial Engineering, Institute of Engineering, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand

a(pornsiri@.sut.ac.th)

Corresponding author. Tel.: +66 44 224264; Fax.: +66 44 22 4604

ABSTRACT: The objectives of this research were to: 1) To evaluate workload of lawn mowing workers in terms of heart rate. and 2) To investigate discomfort placed on different parts of the lawn mowing workers. Eighteen males participated in this study. The average of work experience was 2 years. Heart rates of the operators were measured by the POLAR heart rate monitor. The results showed that the average resting heart rate was 77 beats per minute (bpm). The average working heart rate was 117 bpm. The greatest discomfort score was found in the lower back and the second greatest discomfort score was found in the upper back. The results obtained in this study will be used in work method improvement.

Keywords: heart rate, lawn mowing, operators

1. INTRODUCTION Throughout Thailand, portable lawn movers have been used for which traditional lawn mowers are technically or economically feasible. Lawn mowing task involves long hours of walking, standing and carrying loads, often in hot environment. Although several ergonomic research in working in hot condition have been carried out [1], the health and safety hazards associated with the type of task have not been as thoroughly studied. The portable lawn mower can weigh as much as 10 kilograms when a fuel box is full. Figures 1 and 2 show a worker using a conventional portable lawn mower. This task requires the works to twist their backs in order to control the lawn mower. This increases the likelihood of back pain. The twisting posture has been cited in a number of studies as being related to musculoskeletal disorders [2, 3]. Consequently, the present study was designed to measure and evaluate physiological strains of lawn mowing workers.

Figure 1: A worker using a portable lawn mower.

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Figure 2: A conventional portable lawn mower.

2. OBJECTIVES

1. To evaluate workload of lawn mowing workers in terms of heart rate. 2. To investigate discomfort placed on different parts of the lawn mowing workers.

3. EQUIPMENT 1. Portable lawn mowers 2. Personal computers 3. Heart rate monitoring (POLAR Sport Tester) 4. Questionnaires 5. Stopwatches

4. SUBJECTS

Eighteen subjects participated in this study. They were professional lawn mowing workers who had worked at a university in Thailand. The subjects were paid for their participation based on legal wage. All subjects gave informed consent prior to the study. The demographic characteristics of the subjects are shown in Table 1. The subjects worked on the fixed shift of 8.30 am to 4.00 pm. The time schedule was 90 minutes work and 10 minutes rest.

Table 1: The demographic characteristics of the subjects.

Average Standard deviation Age (years) Body weight (kg) Body height (cm) Experience (years)

34.5 60.1 169.2 4.5

13.2 7.9 6.7 1.8

5. METHOD 5.1 Heart rate measurement

Before performing task, the sensor transmitter of POLAR Sport Tester was placed on the chest of the subjects, whereas the heart rate monitor was placed on their wrists (Figure 3). Resting heart rate was measured before the subject performed the task. Then, the subjects were allowed to work regularly for 90 minutes and rest. Heart rate was obtained at every 15-s interval and continuously monitored through the end of the rest period.

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Figure 3: The locations of the sensor transmitter and the heart rate monitor.

5.2 Evaluation of heart rate during rest period

Brouha [4] used heart rate during rest period as an indicator of cardiac strain. P1, P2, and P3 were the heart rates per minute recorded (beats per minute, bpm) during the last 30 seconds of the 1st, 2nd, and 3rd minutes, respectively, of the recovery period. These recovery heart rates provided a simple measurement of the degree of the cardiac strain induced by work in any environment. The analysis of P1, P2, and P3 is shown in Table 2.

Table 2: The analysis of P1, P2, and P3 as an indicator of cardiac strain.

Condition of cardiac strain Criteria No cardiac strain No recovery Inverse recovery No increasing cardiovascular strain during the day

P1- P3 ≥ 10 bpm and P1, P2, P3 ≤ 90 bpm P1-P3 < 10 bpm and P3 > 90 bpm P3 > 90 bpm and P3-P1≤10 bpm. P1 ≤ 110 bpm and P1-P3 ≥ 10 bpm

5.3 Assessment of discomfort in various parts of body

A 6-point scale was used in this study to assess body part discomfort experienced by the subjects during the lawn mowing operation. The scales used were 0 (no discomfort), 1 (little discomfort), 2 (moderate discomfort), 3 (pain), 4 (much pain), and 5 (extreme pain). The body was divided into 13 parts including upper shoulders, lower shoulders, neck, upper back, lower back, hip, legs, feet, upper arms, elbows, lower arms, wrists, and fingers (Figure 4).

Figure 4: Different parts of body.

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6. RESULTS

The results of heart rate monitoring are shown in Table 3. The resting heart rate varied from 72 to 82 bpm with the average of 77 bpm. The average of heart rate during work was 117 bpm. On average, the mean heart rate during work was 40 bpm greater than that of resting heart rate. The heart rate during work of nine subjects was greater than 115 bpm, which exceeded the maximum of average heart rate recommended by Brouha [4]. Thus, it was very likely that these subjects had cardiac strain.

Table 3: The averages of heart rate during work and resting heart rate.

Subject number

Resting heart rtae (bpm)

Average heart rate during work

(bpm)

Difference between heart rate and

resting heart rate (bpm)

1 74 104.64 30.64 2 76 116.63 40.63 3 77 123.79 46.79 4 77 113.08 36.08 5 79 112.83 33.83 6 80 122.46 42.46 7 74 108.10 34.10 8 82 128.03 46.03 9 78 113.81 35.81

10 75 128.44 53.44 11 81 121.13 40.13 12 76 113.33 37.33 13 74 126.22 52.22 14 74 112.95 38.95 15 77 119.78 42.78 16 79 113.43 34.43 17 72 118.36 46.36 18 80 110.55 30.55

average 76.94 117.09 40.15

The example of heart rate recording is shown in Figure 5. The resting heart rate was 79 bpm, where as the average of heart rate during work was 113 bpm. The P1, P2, and P3 values were 91, 93, 90 bpm, respectively.

Figure 5: Example of heart rate recording.

P1 P2 P3

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Table 4 shows the values of P1, P2, and P3. The P3 values of fourteen subjects were greater than 90 bpm. Furthermore, the values of P1-P3 of seventeen subjects were less than 10 bpm. This means that most subjects were not recovered after three minutes of rest.

Table 4: The values of P1, P2, and P3 obtained from all subjects.

Subject number

P1 (bpm)

P2 (bpm)

P3 (bpm)

P1 - P3 (bpm)

1 99.5 98.0 99.0 0.5 2 97.5 96.0 92.0 5.5 3 98.0 97.0 93.5 4.5 4 94.5 87.5 92.0 2.5 5 90.5 93.5 90.0 0.5 6 98.0 97.0 97.5 0.5 7 81.0 72.5 74.0 7.0 8 92.5 94.5 90.5 2.0 9 94.0 92.0 90.5 3.5

10 93.0 94.0 90.5 2.5 11 90.5 89.0 83.0 7.5 12 99.0 93.5 90.5 8.5 13 92.5 88.0 91.0 1.5 14 99.0 90.5 93.5 5.5 15 92.0 89.0 90.5 1.5 16 94.5 98.0 94.0 0.5 17 91.0 84.5 81.0 10.0 18 83.0 83.0 81.0 2.0

average 93.17 90.97 89.67 3.67

The percentages of subjects who experienced discomfort in different body parts are shown in Table 5. When summing up the percentages of subjects who felt pain (scale 3), much pain (scale 4), and extreme pain (scale 5) in each body part, the top five body parts were lower back (83.32%), upper shoulder (77.77%), upper back (66.65%), lower shoulder (61.09%), and neck (44.43%). The lowest percentage was found in hip area (5.55%). This can be explained that the subjects repetitively twisted their backs during perform the task and therefore leading to lower back pain. Furthermore, carrying the lawn mower all the times resulted in pain in shoulder and back.

Table 5: Percentages of subjects experienced discomfort in different body parts.

Percentage of subject experienced discomfort in difference body part Total Body part

0 1 2 3 4 5 upper shoulders 27.77 5.55 5.55 38.88 16.66 5.55 100.00 lower shoulders 11.11 5.55 5.55 50 16.66 11.11 100.00 neck 11.11 33.33 11.11 27.77 16.66 0 100.00 upper back 11.11 5.55 16.66 16.66 27.77 22.22 100.00 lower back 5.55 0 11.11 22.22 38.88 22.22 100.00 hip 83.33 5.55 5.55 5.55 0 0 100.00 legs 27.77 16.66 27.77 22.22 5.55 0 100.00 feet 66.66 11.11 11.11 11.11 0 0 100.00 upper arms 33.33 27.77 11.11 27.77 0 0 100.00 elbows 66.66 11.11 5.55 16.66 0 0 100.00 lower arms 44.44 11.11 16.66 27.77 0 0 100.00 wrists 33.33 22.22 11.11 33.33 0 0 100.00 fingers 72.22 11.11 5.55 11.11 0 0 100.00

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The result of this study is compared to that obtained from the study of physiological strain of cleaning task carried out by Kumar et al. [5]. In their research, thirteen professional cleaners used cleaning tools when cleaning passenger train wagon for 15 minutes. The average resting heart rates was 72 bpm, whereas the average working heart rate was 105 bpm. Thus, the average working heart rate found in the present study was greater than that found in their study. This was probably due to the longer duration of work and warmer environment.

7. CONCLUSION

From the analysis, it can be concluded that the workload of lawn mowing task caused cardiac strain to most workers. Moreover, the working posture and lawn mower used led to pain in back and shoulder. Redesign of work-rest schedule and modification of lawn mower are needed to assure that the workers can perform the task safely.

REFERENCE

[1] Intaranont, K., (2005). Ergonomics. Chulalongkorn University Press, Bangkok, Thailand. 364 pages.

[2] Calisto, C., Kleisinger, S., (2001). Ergonomics in orchard work evaluation and possible improvements. In: Proceedings of the 13th Triennial Congress of the International Ergonomic Association, Tampere, Finland.

[3] Earle-Richardson, G., Jenkins, P., Fulmer, S., Mason, C., Bresee, C., May, J., (2004). Ergonomic analysis of New York apple harvest work using a posture-activities-tools-handling (PATH) work sampling approach. J. Agric. Safety Health 10(3), 163-176.

[4] Brouha, L., (1967). Physiology in Industry, Pergamon, New York.

[5] Kumar, R., Chaikumarn,M., Kumar, S., (2005). Physiological, subjective and postural loads in passenger train wagon cleaning using a conventional and redesigned cleaning tool. Int. J. Industrial Ergonomics (35), 931-938.

ACKNOWLEDGEMENTS

This study was funded by Suranaree University of Technology, Thailand.

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