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All-terrain vehicle use in agriculture: Exposure to whole body vibration and mechanical shock
Applied Ergonomics 41 (2010) 530–535
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Applied Ergonomics journal homepage: www.elsevier.com/locate/apergo
All-terrain vehicle use in agriculture: Exposure to whole body vibration and mechanical shock Stephan Milosavljevic a, *, Frida Bergman b, Borje Rehn b, Allan B. Carman a a b
Centre for Physiotherapy Research, School of Physiotherapy, University of Otago, PO Box 56, Dunedin, New Zealand Department of Community Medicine and Rehabilitation, Physiotherapy, Umeå University, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 February 2008 Accepted 10 November 2009
Whole body vibration (WBV) and mechanical shock were measured in 12 New Zealand farmers during their daily use of all-terrain vehicles (ATVs). As per the International Organization for Standardization (ISO) guidelines for WBV exposure, frequencies between 0 and 100 Hz were recorded via a seat-pad triaxial accelerometer during 20 min of ATV use. The farmers were also surveyed to estimate seasonal variation in daily ATV usage as well as 7-day and 12-month prevalence of spinal pain. Frequencyweighted vibration exposure and total riding time were calculated to determine the daily vibration dose value (VDV). The daily VDV of 16.6 m/s1.75 was in excess of the 9.1 m/s1.75 action limit set by ISO guidelines suggesting an increased risk of low back injury from such exposure. However, the mean shock factor R, representing cumulative adverse health effects, was 0.31 indicating that these farmers were not exposed to excessive doses of mechanical shock. Extrapolation of daily VDV data to estimated seasonal variations of farmers in ATV riding time demonstrated that all participants would exceed the ISO recommended maximum permissible limits during the spring lambing season, as compared to lower exposures calculated for summer, autumn and winter. Low back pain was the most commonly reported complaint for both 7 day (50%) and 12 month prevalence (67%), followed by the neck (17% and 42%) and the upper back (17% and 25%) respectively. The results demonstrate high levels of vibration exposure within New Zealand farmers and practical recommendations are needed to reduce their exposure to WBV. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Farmers Vibration dose value Low back pain Seasonal variation
1. Introduction Farming is an occupation exposed to whole body vibration (WBV), mechanical shock, awkward postures and heavy manual lifting, which are all accepted as low back pain (LBP) risk factors (Bovenzi et al., 2006; European Union, 2006; Hoy et al., 2005; Lis et al., 2007; Okunribido et al., 2006b). In New Zealand approximately 80,000 all-terrain vehicles (ATVs) are used extensively by farmers during daily work (OSH, 2002). ATV use creates exposure to prolonged WBV and mechanical shock, often in constrained seated postures with twisting of the spine, factors that may be harmful to the musculoskeletal system of the driver (Rehn et al., 2002, 2005; Walker-Bone and Palmer, 2002; Hoy et al., 2005; Bovenzi et al., 2006; European Union, 2006; Lis et al., 2007). ATVs and other offroad vehicles are more likely to produce high levels of WBV and mechanical shocks from operating on uneven terrain as compared to vehicles used on sealed or prepared road surfaces (European * Corresponding author. Tel.: þ64 3 479 7193; fax: þ64 3 479 8414. E-mail address: [email protected] (S. Milosavljevic). 0003-6870/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apergo.2009.11.002
Union, 2006; Rehn, 2004). Vehicle velocity and vehicle make/ structure are also important factors in the generation of WBV and mechanical shock (Hoy et al., 2005). Since daily occupational driving is likely to include both WBVs as well as mechanical shocks it is difficult to distinguish between the adverse health effects of these factors (Hoy et al., 2005; Waters et al., 2007). Although little is known about the effects from mechanical shocks on the spine, it is speculated that damage will result from similar mechanisms to the high compressive forces in heavy lifting (Waters et al., 2007) including fractures in vertebral bodies and endplates with a consequential loss in vertebral height (Brown et al., 2008; Lundin et al., 1998, 2000). Pope et al. (1998) observed increased muscle fatigue in the erector spinae muscles from WBV exposure, and also hypothesized that heavy lifting following such WBV and shock exposure will constitute a higher risk of back injury. While many studies have examined occupational WBV exposure (Bovenzi et al., 2006; Hoy et al., 2005; Johanning et al., 2006; Okunribido et al., 2006a, 2007; Rehn et al., 2005), research into occupational mechanical shocks and their effects on the human
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body have not been as comprehensive. Although the European Union (2006) has set a daily vibration dose value (VDV) of 9.1 m/ s1.75 as an action limit (AL) and 21.0 m/s1.75 as a maximum permissible limit (MPL) risk to the health and safety of an operator is probably greater when such exposure includes transient mechanical shocks (European Union, 2006; Sandover, 1998; Waters et al., 2007). Exposure to multiple mechanical shocks have either been found or hypothesized in a variety of industries (Alem, 2005; Burstrom et al., 2006; ISO, 2004; Khorshid et al., 2007; Mansfield and Marshall, 2001; Okunribido et al., 2007; Rehn et al., 2005; Waters et al., 2007). These shocks are considered to be of higher amplitude, occurring sporadically for a short duration within the daily WBV exposure, and are associated with excessive speed, uneven terrain or obstacles (Hoy et al., 2005; Waters et al., 2007). The International Organization for Standardization (ISO) 2631-1 standard (ISO, 1997) advocates use of the vibration dose value (VDV m/s1.75) as a method for evaluating WBV particularly when the crest factor exceeds 9.0, indicating the presence of mechanical shock. However, the ISO 2631-5 (2004) standard has now been introduced as a guideline for a more direct evaluation of exposure to mechanical shock which is are thought to cause adverse loading on the lumbar disc and lumbar vertebral endplates. Adverse health effects from a combination of both mechanical shock and vibration exposure are thought to include an increased risk of structural and neurological injury to the lumbar spine (Hoy et al., 2005; Bovenzi et al., 2006). Disturbance to the nutrition pathways of spinal articular segments, leading to increased degenerative and pathological processes in the lumbar spine are also speculated (Hadjipavlou et al., 2008). While vibration exposure is usually expressed as root mean square (rms) (in m/s2) or VDV(in m/s1.75), shock exposure is usually expressed as the daily equivalent static compression dose, Sed (in MPa) or as a working lifetime exposure to shocks (expressed as factor R). ISO thresholds for expected risk associated with such exposures have also been published (ISO, 1997, 2004; European Union, 2006) and are used as benchmarks for vibration and shock exposure within this manuscript. The aims of this study are to use the International Organization for Standardization guidelines (ISO 2631-1 and 2631-5) to determine WBV and mechanical shock exposure on New Zealand farmers who regularly use ATVs in their daily work activities. It is hypothesized that exposures will exceed ISO recommended limits and be a factor in increased risk of LBP. Results from the present study will assist in developing recommendations to minimize exposures to WBV and mechanical shock during ATV operation by either changing farmer driving practices or ATV/seat suspension design.
regularly used ATVs and with a mean 29.6 years of experience, represented typical New Zealand mixed stock farmers. For the purposes of recruitment and due to the limitations of researchers’ travel participants were recruited from farms that were located within a 2 h drive from the University of Otago. Experiments were conducted on the property of each farmer on two typical working days with all farmers using their own ATV. The study was approved by the University of Otago Human Ethics committee. 2.2. Experimental protocol Exposure of the participant to WBV while operating their ATV was collected during the first on-farm visit (Fig. 1). Exposure to WBV was measured in accordance to ISO 2631-1 and 2631-5 standards when each farmer was sitting on a custom made rubberized seat pad containing a tri-axial accelerometer (constructed by Scott Parsons Electronics (SPE) in Albany, Western Australia using 2 biaxial iMEMSÒ ADXL210–10 g gravitational accelerometers). The accelerometer axes were aligned; X – anterior–posterior, Y – mediolateral, and Z – superior–inferior with the ATV. The farmers were asked to ride their ATV for approximately 20 min on a typical daily work route of their choice. Data were digitally stored in a purposefully built 6 channel data logger (SPE LoggersÒ – Australia) mounted and strapped to the rear carrying rack of the ATV (Fig. 1). The sampling frequency was 200 Hz with an anti-aliasing filter set at 100 Hz. 2.3. Total riding time To obtain a representative total ATV daily riding time for each farmer, a second on-farm visit was required. During this visit a triaxial accelerometer of the same design was secured in a watertight housing and fastened with screws to the top of an ATV helmet mounted on the head of each farmer. The helmet was a commercially available and size adjustable unit. This accelerometer was connected to the data logger (SPE LoggersÒ) via a cable with an inline plug. Each farmer was instructed to firmly put the helmet on and attach the cable to the data logger when sitting on the ATV. Conversely when leaving the ATV, the cable was to be unplugged and helmet removed. In this way, the total riding time of the ATV for a workday could be determined by the accumulation of helmet vibration data episodes. Helmet mounted vibration data were also gathered for future analysis of head/neck vibration of farmers.
2. Material and methods 2.1. Participants Twelve mixed stock farmers (Table 1) were recruited from the South Otago rural population of New Zealand. South Otago is representative of the classical New Zealand rolling lowland mixed stock farm. These farmers were highly experienced, self-employed,
Table 1 Characteristics of recruited farmers (n ¼ 12 males). Variable
Min
Max
Mean
SD
Age (yrs) Height (m) Weight (kg) BMI (kg/m2) Farming experience (yrs)
41.0 1.70 75.0 22.2 15.0
62.0 1.85 110.0 32.8 44.0
49.6 1.78 90.0 28.4 29.6
7.1 0.05 9.4 2.8 8.1
531
Fig. 1. ATV with data logger mounted on the rear carrying rack.
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2.4. Data analysis Vibration exposure was expressed as the daily vibration dose value (VDV). The use of the VDV, as opposed to root mean square (RMS) to measure exposure, followed ISO 2631-1 recommendations as the measure is more sensitive to the amplitude peaks that are associated with shock (ISO, 1997). In order to confirm the use of the VDV as an appropriate exposure measure the maximum crest factor for the Z direction was calculated for each farmer. A mean crest factor in excess of 9.0 would justify use of the VDV as a more sensitive indicator of shock (ISO, 1997). The acceleration dose for mechanical shock was calculated in accordance with the ISO 2631-5 standard from the same ATV seat pad accelerations. The risk of adverse health effects from exposure to mechanical shock was obtained by comparing the acceleration dose with established exposure limits (ISO, 2004). Calculation of both VDV and exposure to mechanical shock are explained below. 2.5. Whole body vibration – vibration dose value (VDV) Following ISO 2631-1 recommended frequency weighting, VDVs in the X, Y, and Z orthogonal directions were calculated (Eq. (1)) as the weighted fourth power of acceleration.
2 VDVi ¼ wi 4
ZT
314 4
a ðtÞdt 5
(1)
0
where awi is the frequency-weighted acceleration with values of wX ¼ 1.4, wY ¼ 1.4, wZ ¼ 1.0 (ISO, 1997). The total VDV (tVDV) over the collection period was then calculated as the vector sum (Eq. (2)) of VDV obtained for each direction of vibration.
tVDV ¼
VDV4x þ VDV4y þ VDV4z
1 4
(2)
The VDV obtained from each participant’s 20 min data collection sample (T20) was then used to calculate a daily VDV by extrapolation to the total riding time (Ttotal) as recorded from the helmet (Eq. (3)).
VDV ¼ VDVt
1 Ttotal 4 T20
(3)
2.6. Mechanical shock – calculation of the spinal response acceleration dose
"
X
#1=6 A6ik
Dkd ¼ Dk
td tm
1=6
(5)
The daily equivalent static compression dose, Sed, was calculated by a weighted sum of the three orthogonal daily acceleration dose values where mX equals 0.015 MPa/(m/s2), mY equals 0.035 MPa/(m/ s2) and mZ equals 0.032 MPa/(m/s2) (Eq. (6)).
2 Sed
¼ 4
X
31=6 ðnk Dkd Þ
65
(6)
k ¼ x;y;z
Factor R is the ratio between the static compression dose and the ultimate strength of the lumbar spine for a person. R represents the risk of obtaining chronic injury and is used in the assessment of the adverse health effects related to the human response acceleration dose (Eq. (7)).
2 R ¼ 4
n X Sed N1=6 Sui c i¼1
!6 31=6 5
(7)
where n is the number of years of exposure; N is the number of exposure days per year; Sui is the ultimate strength of the lumbar spine adjusted for the age at which exposure starts ‘b’ and years of exposure ‘i’, with Sui (MPa) ¼ 6.75 0.966(b þ i); and ‘c’ is a constant representing the static stress due to gravitational force. A recommended value for ‘c’ is 0.25 MPa for driving posture (ISO, 2004). In accordance with the recommendations of the ISO 2631-5 the health effects for the present study are evaluated by: An Sed < 0.5 MPa indicates a low probability of adverse health effects An Sed > 0.8 MPa indicates a high probability of adverse health effects A Factor R < 0.8 indicates a low probability of adverse health effects A Factor R > 1.2 indicates a high probability of adverse health effects
2.7. Survey of seasonal ATV use and spinal pain
The collected acceleration data from the ATV seat pad was resampled at 160 Hz in accordance with the recommendations of the ISO 2631-5 standard for investigating shock. Using spinal stress methods detailed in the ISO 2631-5, lumbar spine accelerations in the X, Y and Z directions (alX, alY, alZ) were determined in response to the accelerations measured at the seat pad (ISO, 2004). The acceleration dose, Dk, in metres per second squared, for each direction was calculated as the sixth power of acceleration (Eq. (4)).
Dk ¼
workday, the average daily dose, Dkd, in metres per second squared, was calculated where td is the duration of the daily exposure, and tm is the period over which Dk has been measured (Eq. (5)).
(4)
Although the present data collection took place in winter; it is known that there are seasonal variations in ATV use with peak usage occurring during the spring lambing period in New Zealand (Knight et al., 2005). The participants were therefore surveyed with a modified version of the whole body vibration health surveillance questionnaire (WBVHSQ) developed by Pope and colleagues (Pope et al., 2002). This modified questionnaire specifically asked the farmers to estimate their typical daily seasonal (winter, spring, summer, autumn) ATV usage. The modified WBVHSQ also asked the participants whether they had suffered from low back, upper back or neck pain within the past 7 days and within the past 12 months.
i
2.8. Statistical analysis where Aik is the ith peak of the lumbar spine acceleration response alk(t) and ‘k’ corresponds to the X, Y and Z axes. For X and Y directions, both the positive and negative peaks were counted. For the z direction only the positive peaks were counted, since it is the compression forces on the spine during shocks that are of interest for exposure severity (ISO, 2004). In order to scale the dose to an average
Filtering of vibration data and calculation of all derived quantities of WBV and mechanical shock were carried out using LabView 8.0tm. The personal and demographic data, as well as the sampled and calculated daily and annual exposure to WBV (as the VDV) and mechanical shock are presented descriptively in Tables 1 and 2. For
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Table 2 Calculation of daily vibration dose value (VDV) and acceleration dose per axis, static compression dose, and risk factor R. Whole body vibration
Mechanical shock
Farmer
Time 20
VDVX
VDVY
VDVZ
Sum20
DRT
VDVDRT
DX
DY
DZ
DXD
DYD
DZD
Sed
D/Y
Exp.
R
1 2 3 4 5 6 7 8 9 10 11 12
18.4 29.2 25.1 26.8 26.0 14.4 22.1 20.2 26.5 18.2 22.1 25.6
9.5 5.4 13.5 9.7 8.9 6.9 11.0 9.2 8.0 6.9 9.3 6.6
7.2 5.1 14.1 10.1 8.1 6.1 11.0 7.3 7.4 7.5 7.9 8.1
11.6 7.2 14.2 11.0 8.7 6.8 11.7 8.2 9.5 8.4 10.7 7.6
13.0 8.0 18.3 13.6 11.3 8.8 14.8 11.0 11.1 10.1 12.5 9.9
45.6 125.2 196.3 117.8 40.2 68.8 83.2 13.3 56.3 122.6 190.8 88.8
16.3 11.6 30.6 19.7 12.6 13.0 20.6 9.9 13.5 16.3 21.4 13.5
5.34 2.40 7.33 5.51 4.68 4.09 6.57 4.92 4.85 3.45 4.41 3.49
3.58 2.77 6.57 4.84 4.50 3.60 6.00 3.35 3.88 4.37 4.39 4.89
9.16 3.69 9.48 6.16 4.42 4.21 8.29 4.66 5.09 4.56 8.17 4.96
6.2 3.1 10.3 7.1 5.0 5.3 8.2 4.6 5.5 4.7 6.3 4.3
4.2 3.5 9.3 6.2 4.8 4.7 7.5 3.1 4.4 6.0 6.3 6.0
10.7 4.7 13.4 7.9 4.8 5.5 10.3 4.3 5.8 6.3 11.7 6.1
0.34 0.16 0.44 0.27 0.18 0.19 0.34 0.15 0.19 0.23 0.38 0.23
250 364 364 300 325 350 300 364 350 336 350 294
42 30 25 15 22 30 28 24 33 44 34 28
0.50 0.20 0.47 0.26 0.18 0.25 0.38 0.17 0.23 0.33 0.48 0.24
Mean SD Min Max
22.9 4.4 14.4 29.2
8.7 2.2 5.4 13.5
8.3 2.4 5.1 14.1
9.6 2.2 6.8 14.2
11.9 2.8 8.0 18.3
95.7 57.3 13.3 196.3
16.6 5.8 9.9 30.6
4.75 1.36 2.40 7.33
4.40 1.09 2.77 6.57
6.07 2.11 3.69 9.48
5.89 1.94 3.06 10.33
5.50 1.74 3.12 9.26
7.61 3.10 4.35 13.36
0.26 0.10 0.15 0.44
328.9 35.9 250 364
29.6 8.1 15.0 44.0
0.31 0.12 0.17 0.50
Key – Whole body vibration: Time 20 ¼ approximately 20-min riding sample; VDVX, VDVY and VDVZ ¼ 20-min vibration dose values in X, Y and Z directions (m/sec1.75); Sum20 ¼ Vector summation of X þ Y þ Z; DRT ¼ daily riding time (in min); VDVDRT ¼ calculated daily VDV (m/sec1.75). Key – Mechanical shock: DX, DY, and DZ ¼ 20-min acceleration dose (m/sec2) in X, Y and Z directions; DXD, DYD, and DZD ¼ Daily acceleration dose (m/sec2) in X, Y and Z directions; Sed ¼ Daily equivalent static compression doses in MPa; D/Y ¼ Days of exposure per year; Exp. ¼ Years of experience; R ¼ Factor R.
the purposes of determining a predicted seasonal daily VDV exposure a mean ratio between estimated ATV usage in winter and actual ATV usage from the helmet mounted accelerometer was calculated, and applied to the WBVHSQ survey to estimate exposure for spring lambing, spring other than lambing, summer and autumn. These survey data thus allowed the estimation of seasonal daily ATV riding time and seasonal VDV exposure as well as the total days per week and days per year of ATV use; information that was required for calculating working lifetime exposure for mechanical shock (Factor R). The presentation of these daily and yearly WBV and shock exposure calculations allows a comparison to the ISO 2631-1 and ISO 2631-5 AL and MPL for adverse health effects amongst New Zealand farmers. 3. Results 3.1. Vibration dose value (VDV) Each farmer rode their ATV for a mean of 22.9 min (Table 2). The crest factor in the Z direction had a mean score of 9.5 within a range of 7.8–11.9 exceeding the recommended threshold exposure for the use of the VDV. The filtered and weighted vibration data for this time period produced similar X, Y and Z mean VDV scores of 8.7, 8.3 and 9.6 m/sec1.75, respectively and were vector summated (ISO 2631-1 guideline) for a resultant VDV of 11.9 m/sec1.75. Each of these calculated time/dose VDV samples were then extrapolated to the full day riding time per day (mean 95.7 min) to obtain an estimated mean daily VDV of 16.6 m/sec1.75 (Table 2). The 95.7 min vector summated VDV of 16.6 m/sec1.75 was then entered into the VDV equation to calculate a VDV AL (9.1 m/sec1.75) and MPL (21.0 m/sec1.75) would be reached after 8.0 min and 220.8 min respectively of ATV use for these farmers under these conditions. All 12 farmers had estimated daily VDV scores (DRT Sum – Table 2) that exceeded the AL with two farmers (Farmer 3 & 11 – Table 2) exceeding the MPL. 3.2. Mechanical shock exposure
22.9-min riding sample. The Sed score of each farmer was then extrapolated to their full day riding time giving a mean daily Sed of 0.26 MPa (Table 2). This value represents a low probability of an adverse health effect (Sed < 0.5 MPa) in terms of ISO 2631-5. Based on Table 2, farmers rode their ATV for a mean of 328.9 days per year. The age at which the exposure to shocks started was estimated by subtracting years of experience from current age. A mean factor R was then calculated for each farmer (mean 0.3) with no farmers demonstrating a score approaching 0.8, the lower limit of the ISO 2631-5 recommendations. 3.3. Spinal pain survey Low back pain was the most commonly reported complaint for both 7-day (50%) and 12-month prevalence (67%), followed by the neck (17% and 42%) and the upper back (17% and 25%), respectively (Table 3). 3.4. Seasonal variation The recorded winter season ATV daily riding time (mean of 95.7 min) was compared to the farmer estimated winter season use (mean of 156.0 min) extracted from the WBVHSQ (Table 4). These data were used to calculate a ratio of 0.62 between recorded and farmer estimated ATV exposure which was then applied to all farmer estimated seasonal daily riding times. Thus a farmer using an ATV during summer was calculated as having a mean vibration exposure time of 138.0 min, in autumn 114.0 min, in winter 95.7 min (recorded), in spring (non-lambing) 192.0 min and in spring lambing 318.0 min.
Table 3 Seven day and 12 month prevalence of back and neck pain. LBP 7 Pain Yes (n¼) Pain No (n¼) Percent Yes
The seat pad measured accelerations yielded mean acceleration dose values of 4.75, 4.40 and 6.07 m/s2 for the X, Y and Z direction respectively, with a resultant mean Sed value of 0.20 MPa for the
LBP 12
UBP 7
UBP 12
CxP 7
CxP 12
6 6
8 4
2 10
3 9
2 10
5 7
50
67
17
25
17
42
Key: LBP 7, Low back pain in past 7 days; LBP 12, Low back pain in past 12 months; UBP 7, Upper back pain in past 7 days; UBP 12, Upper back pain in past 12 months; CxP 7, Neck pain in past 7 days; CxP 12, Neck pain in past 12 months.
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Table 4 Seasonal, weekly and daily use of ATV in a sample of New Zealand sheep farmers (mean SD). Season
DPW
DRT Est
Spring lambing Spring non-lambing Summer Autumn Winter
7.0 6.6 5.6 5.5 6.7
510.0 312.0 222.0 180.0 156.0
(0.0) (0.7) (1.1) (1.1) (0.7)
(144.0)b (156.0)b (126.0)b (126.0)b (72.0)b
DRT 318.0 192.0 138.0 114.0 95.7
(90.0)c (96.0)c (78.0)c (78.0)c (57.3)a
Key – Note: Duration of lambing was 34.3 7.5 days; DPW Farmer estimated days per week of ATV usage; DRT Est Farmer estimated ATV daily riding time in minutes; DRT Actual and calculated daily riding time in minutes. a Actual daily riding time measured from helmet accelerometer. b Estimated daily riding time from survey data. c Calculated seasonal daily riding time.
In terms of survey 50% (n ¼ 6) of these farmers experienced low back pain during the past 7 days and 67% (n ¼ 8) during the past 12 months. Although only 12 farmers were surveyed, this is consistent with the high prevalence of low back pain and musculoskeletal disorders observed in occupations using ATVs (Firth et al., 2002; Rehn et al., 2002; Walker-Bone and Palmer, 2002). As the shock doses for these farmers were low, it is more likely that the high doses of WBV, and not shock are the risk factor for the development of low back pain. Other factors such as the sustained flexed and seated postures used while driving the ATV, and frequent heavylifting work tasks associated with farming and often taken in series with ATV riding, are also likely to account for the high prevalence of low back pain among farmers. 4.1. Limitations
4. Discussion The mean daily VDV sum exposure for farmers using ATVs is high (16.6 m/sec1.75), exceeding the ISO recommended AL (9.1 m/ sec1.75) after 8.0 min and exceeding the recommended MPL (21.0 m/sec1.75) after 220.8 min. The 12 month prevalence of LBP was also high and similar to that of New Zealand farmers previously recorded by Firth et al. (2002). Twelve month prevalence of neck pain at 42% is also high supporting previous research on ATV WBV vibration exposures in Sweden (Rehn et al., 2002). Despite such high levels of vibration exposure, the risk exposure from mechanical shock was shown to be low. If the calculations for seasonally adjusted ATV riding time hold true we would expect that these farmers exceed the calculated MPL (220.8 min) during the spring lambing season (approximately 34 days) placing them at a high risk of developing vibration induced low back pain. All calculations for VDV exposures also demonstrate that these farmers consistently exceeded the AL during the sampled day. It is likely that farmers exceeded the AL on typical farm work days during each season by a considerable amount, placing them at some risk of WBV induced low back pain. Paradoxically participants were not exposed to shock in terms of doses exceeding the Sed lower limit of 0.5 MPa, or lifetime exposure of 0.8 for risk factor R, indicating a low probability of adverse health effects from ATV induced shock exposure associated with farming. Furthermore, factor R ranged from 0.20 to 0.50 demonstrating a low shock exposure from ATV use, particularly where some of these participants had been farming for at least 40 years. However, the calculations for Factor R are reliant on using this recorded VDV exposure as a constant throughout the work year and over working lifetime. We did not record day to day variations in vibration exposure for these farmers and it is also likely that considerable seasonal and yearly variations occur. Over time, these unknown factors are likely to have a summative effect on cumulative shock loadings expressed as Sed and Factor R and as such, our results could either over or underestimate cumulative shock exposure. Although a number of studies have suggested that exposure to severe shock events can occur with WBV exposure (Hoy et al., 2005; Johanning et al., 2006; Okunribido et al., 2006a, 2007; Rehn et al., 2005), these authors have not used the recommended ISO 2631-5 standard to investigate the adverse health effects associated with shock (Alem, 2005). To our knowledge, only two studies have investigated the influence of shock on humans. Burstrom et al. (2006) used the ISO 2631-5 standard to investigate shock doses to aircraft cabin attendants during aircraft landing. Khorshid et al. (2007) measured WBV and shocks in motor vehicles crossing different speed control humps during urban driving. As there is no published shock exposure measurements from agricultural vehicle use comparisons cannot be made. It will require further research with a larger sample of farmers to verify these results.
It is possible that a 20-min riding sample is a poor representation of the true WBV and shock exposure for these farmers during a regular workday and may not represent the true risk of adverse health effects from ATV use. The relatively large uncertainty of WBV measurements reflecting true daily WBV exposure (15–40% variability), has been recently investigated (Pinto and Stacchini, 2006) and may be a factor in determining the true risk of adverse health effects. Although we tested experienced farmers, due to the small sample size it is also difficult to generalize the findings to all farmers who drive ATVs. We also did not quantify the postures employed by these farmers when sitting on the ATVs. Although variations in seated posture will likely have an effect on vibration exposure and transmissibility, neither ISO 2631-1 nor 2631-5 currently address the potential effects of such posture. While the farmers were asked to drive their ATV on a typical farm route on their own farm, it may be that they chose a path that was of relatively even terrain and familiar to them. Participation in the study might have also made them more cautious than normal, thereby not travelling at speeds that they would on a normal workday. Although this 20-min riding sample may be representative of different surface induced WBV, the shock dosage may be less than that of a regular workday when farmers are driving on more uneven terrain, and undertaking everyday farming tasks. If this assertion holds true, the results from this study will underestimate total exposure to mechanical shock from ATV use in farmers. 5. Conclusion The present findings indicate farmers are exposed to very high levels of WBV during daily use of an ATV, and particularly during the busy spring lambing season. This exposure in combination with a constrained seated posture and physically demanding work tasks is likely to be a substantial risk factor for the development of occupational low back pain, at least in this sample of New Zealand farmers. Although mean daily Sed value appeared to be within safe limits at 0.26 MPa the data for this measure also demonstrated considerable variability amongst the 12 farmers (0.15–0.44 MPa) indicating that a larger sample over a greater length of time might be required to calculate this factor with any confidence. The calculation of a working lifetime risk factor R of 0.31 is also well below the ISO 2631-5 recommended lower limit of 0.5 and 0.8 respectively, generally indicating a low probability of adverse health effects from ATV induced mechanical shock exposure. Acknowledgements We thank Scott Parsons and Steve Slack, electronics engineers from Scott Parsons Electronics (SPELEC) in Albany, Western
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Australia, for sourcing accelerometers and data logging hardware as well as constructing the weather resistant, robust housing needed to mount these devices on the ATV and helmet. References Alem, N., 2005. Application of the new ISO 2631-5 to health hazard assessment of repeated shocks in U.S. army vehicles. Ind. Health 43, 403–412. Bovenzi, M., Rui, F., Negro, C., D’Agostino, F., Angotzi, G., Bianchi, S., Bramanti, L., Festa, G., Gatti, S., Pionto, I., Rondina, L., Stacchini, N., 2006. An epidemiological study of low back pain in professional drivers. J. Sound Vib. 298, 514–539. Brown, S.H.M., Gregory, D.E., McGill, S.M., 2008. Vertebral end-plate fractures as a result of high rate pressure loading in the nucleus of the young adult porcine spine. J. Biomech. 41, 122–127. Burstrom, L., Lindberg, L., Lindgren, T., 2006. Cabin attendants’ exposure to vibration and shocks during landing. J. Sound Vib. 298, 601–605. European Union, 2006. Guide to Good Practice on Whole Body Vibration. Directive 2002/44/EC on Minimum Health and Safety. European Commission Directorate General Employment. Social Affairs and equal Opportunities. Firth, H., Herbison, P., McBribe, D., Feyer, A.-M., 2002. Low back pain among farmers in Southland, NZ. J. Occup. Health Saf. Aust. NZ. 18, 167–171. Hadjipavlou, A.G., Tzermiadianos, M.N., Bogduk, N., Zindrick, M.R., 2008. The pathophysiology of disc degeneration: a critical review. J. Bone Joint Surg. 90, 1261–1270. Hoy, J., Mubarak, N., Nelson, S., Sweerts de Landas, M., Magnusson, M., Okunribido, O., Pope, M., 2005. Whole body vibration and posture as risk factors for low back pain among forklift truck drivers. J. Sound Vib. 284, 933–946. ISO, 1997. Guide to the Evaluation of Human Exposure to Whole-body Mechanical Vibration and Shock. International Organization for Standardization. ISO 2631-1. ISO, 2004. Mechanical Vibration and Shock – Evaluation of Human Exposure to Whole Body Vibration – Part 5: Method for Evaluation of Vibration Containing Multiple Shocks. ISO 2631-2635. International Organization for Standardization. Johanning, E., Landsbergis, P., Fischer, S., Christ, E., Gores, B., Luhrman, R., 2006. Whole-body vibration and ergonomic study of US railroad locomotives. J. Sound Vib. 298, 594–600. Khorshid, E., Alkalby, F., Kamal, H., 2007. Measurement of whole-body vibration exposure from speed control humps. J. Sound Vib. 304, 640–659. Knight, T., Waters, W., Tarbotton, I., 2005. A literature review and survey of farmers views on factors contributing to high survival among multiple born lambs with an emphasis on triplet lambs. Meat and Wool New Zealand. Project No: 03AR64.
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Lis, A.M., Black, K.M., Korn, H., Nordin, M., 2007. Association between sitting and occupational LBP. Eur. Spine J. 16, 283–298. Lundin, O., Ekstrom, L., Hellstrom, M., Holm, S., Sward, L., 1998. Injuries in the adolescent porcine spine exposed to mechanical compression. Spine 23, 2574–2579. Lundin, O., Ekstrom, L., Hellstrom, M., Holm, S., Sward, L., 2000. Exposure of the porcine spine to mechanical compression: differences in injury pattern between adolescents and adults. Eur. Spine J. 9, 466–471. Mansfield, N.J., Marshall, J.M., 2001. Symptoms of musculoskeletal disorders in stage rally drivers and co-drivers. Br. J. Sports Med. 35, 314–320. Okunribido, O.O., Magnusson, M., Pope, M., 2006a. Low back pain in drivers: the relative role of whole body vibration, posture and manual material handling. J. Sound Vib. 298, 540–555. Okunribido, O.O., Magnusson, M., Pope, M., 2006b. Delivery drivers and low-back pain: a study of the exposures to posture demands, manual materials handling and whole-body vibration. Int. J. Ind. Ergon. 36, 265–273. Okunribido, O.O., Shimbles, S.J., Magnusson, M., Pope, M., 2007. City bus driving and low back pain: a study of the exposures to posture demands, manual materials handling and whole-body vibration. Appl. Ergon. 38, 29–38. OSH, 2002. Safe Use of ATVs on New Zealand Farms. Occupational Safety and Health Service, Department of Labour, Wellington, New Zealand. Pinto, I., Stacchini, N., 2006. Uncertainty in the evaluation of occupational exposure to whole-body vibration. J. Sound Vib. 298, 556–562. Pope, M., Wilder, D.G., Magnusson, M., 1998. Possible mechanisms of low back pain due to whole body vibration. J. Sound Vib. 215, 687–697. Pope, M., Magnusson, M., Lundstrom, R., Hulshof, C., Verbeek, J., Bovenzi, M., 2002. Guidelines for whole body vibration health surveillance. J. Sound Vib. 253, 131–167. Rehn, B., Bergdahl, I.A., Ahlgren, C., From, C., Jarvholm, B., Lundstrom, R., Nilsson, T., Sundelin, G., 2002. Musculoskeletal symptoms amongst drivers of all-terrain vehicles. J. Sound Vib. 253, 21–29. Rehn, B., 2004. Musculoskeletal disorders and whole-body vibration exposure among professional drivers of all-terrain vehicles, dissertation, Umea University, Department of Public Health and Clinical Medicine. Rehn, B., Nilsson, T., Olofsson, B., Lundstrom, R., 2005. Whole-body vibration exposure and non-neutral neck postures during occupational use of all-terrain vehicles. Ann. Occup. Hyg. 49, 267–275. Sandover, J., 1998. High acceleration events: an introduction and review of expert opinion. J. Sound Vib. 215, 927–945. Walker-Bone, K., Palmer, K.T., 2002. Musculoskeletal disorders in farmers and farm workers. Occ. Med. 52, 441–450. Waters, T., Rauche, C., Genaidy, A., Rashed, T., 2007. A new framework for evaluating potential risk of back disorders due to whole body vibration and repeated mechanical shock. Ergonomics 50, 379–395.
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Applied Ergonomics journal homepage: www.elsevier.com/locate/apergo
All-terrain vehicle use in agriculture: Exposure to whole body vibration and mechanical shock Stephan Milosavljevic a, *, Frida Bergman b, Borje Rehn b, Allan B. Carman a a b
Centre for Physiotherapy Research, School of Physiotherapy, University of Otago, PO Box 56, Dunedin, New Zealand Department of Community Medicine and Rehabilitation, Physiotherapy, Umeå University, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 February 2008 Accepted 10 November 2009
Whole body vibration (WBV) and mechanical shock were measured in 12 New Zealand farmers during their daily use of all-terrain vehicles (ATVs). As per the International Organization for Standardization (ISO) guidelines for WBV exposure, frequencies between 0 and 100 Hz were recorded via a seat-pad triaxial accelerometer during 20 min of ATV use. The farmers were also surveyed to estimate seasonal variation in daily ATV usage as well as 7-day and 12-month prevalence of spinal pain. Frequencyweighted vibration exposure and total riding time were calculated to determine the daily vibration dose value (VDV). The daily VDV of 16.6 m/s1.75 was in excess of the 9.1 m/s1.75 action limit set by ISO guidelines suggesting an increased risk of low back injury from such exposure. However, the mean shock factor R, representing cumulative adverse health effects, was 0.31 indicating that these farmers were not exposed to excessive doses of mechanical shock. Extrapolation of daily VDV data to estimated seasonal variations of farmers in ATV riding time demonstrated that all participants would exceed the ISO recommended maximum permissible limits during the spring lambing season, as compared to lower exposures calculated for summer, autumn and winter. Low back pain was the most commonly reported complaint for both 7 day (50%) and 12 month prevalence (67%), followed by the neck (17% and 42%) and the upper back (17% and 25%) respectively. The results demonstrate high levels of vibration exposure within New Zealand farmers and practical recommendations are needed to reduce their exposure to WBV. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Farmers Vibration dose value Low back pain Seasonal variation
1. Introduction Farming is an occupation exposed to whole body vibration (WBV), mechanical shock, awkward postures and heavy manual lifting, which are all accepted as low back pain (LBP) risk factors (Bovenzi et al., 2006; European Union, 2006; Hoy et al., 2005; Lis et al., 2007; Okunribido et al., 2006b). In New Zealand approximately 80,000 all-terrain vehicles (ATVs) are used extensively by farmers during daily work (OSH, 2002). ATV use creates exposure to prolonged WBV and mechanical shock, often in constrained seated postures with twisting of the spine, factors that may be harmful to the musculoskeletal system of the driver (Rehn et al., 2002, 2005; Walker-Bone and Palmer, 2002; Hoy et al., 2005; Bovenzi et al., 2006; European Union, 2006; Lis et al., 2007). ATVs and other offroad vehicles are more likely to produce high levels of WBV and mechanical shocks from operating on uneven terrain as compared to vehicles used on sealed or prepared road surfaces (European * Corresponding author. Tel.: þ64 3 479 7193; fax: þ64 3 479 8414. E-mail address: [email protected] (S. Milosavljevic). 0003-6870/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apergo.2009.11.002
Union, 2006; Rehn, 2004). Vehicle velocity and vehicle make/ structure are also important factors in the generation of WBV and mechanical shock (Hoy et al., 2005). Since daily occupational driving is likely to include both WBVs as well as mechanical shocks it is difficult to distinguish between the adverse health effects of these factors (Hoy et al., 2005; Waters et al., 2007). Although little is known about the effects from mechanical shocks on the spine, it is speculated that damage will result from similar mechanisms to the high compressive forces in heavy lifting (Waters et al., 2007) including fractures in vertebral bodies and endplates with a consequential loss in vertebral height (Brown et al., 2008; Lundin et al., 1998, 2000). Pope et al. (1998) observed increased muscle fatigue in the erector spinae muscles from WBV exposure, and also hypothesized that heavy lifting following such WBV and shock exposure will constitute a higher risk of back injury. While many studies have examined occupational WBV exposure (Bovenzi et al., 2006; Hoy et al., 2005; Johanning et al., 2006; Okunribido et al., 2006a, 2007; Rehn et al., 2005), research into occupational mechanical shocks and their effects on the human
S. Milosavljevic et al. / Applied Ergonomics 41 (2010) 530–535
body have not been as comprehensive. Although the European Union (2006) has set a daily vibration dose value (VDV) of 9.1 m/ s1.75 as an action limit (AL) and 21.0 m/s1.75 as a maximum permissible limit (MPL) risk to the health and safety of an operator is probably greater when such exposure includes transient mechanical shocks (European Union, 2006; Sandover, 1998; Waters et al., 2007). Exposure to multiple mechanical shocks have either been found or hypothesized in a variety of industries (Alem, 2005; Burstrom et al., 2006; ISO, 2004; Khorshid et al., 2007; Mansfield and Marshall, 2001; Okunribido et al., 2007; Rehn et al., 2005; Waters et al., 2007). These shocks are considered to be of higher amplitude, occurring sporadically for a short duration within the daily WBV exposure, and are associated with excessive speed, uneven terrain or obstacles (Hoy et al., 2005; Waters et al., 2007). The International Organization for Standardization (ISO) 2631-1 standard (ISO, 1997) advocates use of the vibration dose value (VDV m/s1.75) as a method for evaluating WBV particularly when the crest factor exceeds 9.0, indicating the presence of mechanical shock. However, the ISO 2631-5 (2004) standard has now been introduced as a guideline for a more direct evaluation of exposure to mechanical shock which is are thought to cause adverse loading on the lumbar disc and lumbar vertebral endplates. Adverse health effects from a combination of both mechanical shock and vibration exposure are thought to include an increased risk of structural and neurological injury to the lumbar spine (Hoy et al., 2005; Bovenzi et al., 2006). Disturbance to the nutrition pathways of spinal articular segments, leading to increased degenerative and pathological processes in the lumbar spine are also speculated (Hadjipavlou et al., 2008). While vibration exposure is usually expressed as root mean square (rms) (in m/s2) or VDV(in m/s1.75), shock exposure is usually expressed as the daily equivalent static compression dose, Sed (in MPa) or as a working lifetime exposure to shocks (expressed as factor R). ISO thresholds for expected risk associated with such exposures have also been published (ISO, 1997, 2004; European Union, 2006) and are used as benchmarks for vibration and shock exposure within this manuscript. The aims of this study are to use the International Organization for Standardization guidelines (ISO 2631-1 and 2631-5) to determine WBV and mechanical shock exposure on New Zealand farmers who regularly use ATVs in their daily work activities. It is hypothesized that exposures will exceed ISO recommended limits and be a factor in increased risk of LBP. Results from the present study will assist in developing recommendations to minimize exposures to WBV and mechanical shock during ATV operation by either changing farmer driving practices or ATV/seat suspension design.
regularly used ATVs and with a mean 29.6 years of experience, represented typical New Zealand mixed stock farmers. For the purposes of recruitment and due to the limitations of researchers’ travel participants were recruited from farms that were located within a 2 h drive from the University of Otago. Experiments were conducted on the property of each farmer on two typical working days with all farmers using their own ATV. The study was approved by the University of Otago Human Ethics committee. 2.2. Experimental protocol Exposure of the participant to WBV while operating their ATV was collected during the first on-farm visit (Fig. 1). Exposure to WBV was measured in accordance to ISO 2631-1 and 2631-5 standards when each farmer was sitting on a custom made rubberized seat pad containing a tri-axial accelerometer (constructed by Scott Parsons Electronics (SPE) in Albany, Western Australia using 2 biaxial iMEMSÒ ADXL210–10 g gravitational accelerometers). The accelerometer axes were aligned; X – anterior–posterior, Y – mediolateral, and Z – superior–inferior with the ATV. The farmers were asked to ride their ATV for approximately 20 min on a typical daily work route of their choice. Data were digitally stored in a purposefully built 6 channel data logger (SPE LoggersÒ – Australia) mounted and strapped to the rear carrying rack of the ATV (Fig. 1). The sampling frequency was 200 Hz with an anti-aliasing filter set at 100 Hz. 2.3. Total riding time To obtain a representative total ATV daily riding time for each farmer, a second on-farm visit was required. During this visit a triaxial accelerometer of the same design was secured in a watertight housing and fastened with screws to the top of an ATV helmet mounted on the head of each farmer. The helmet was a commercially available and size adjustable unit. This accelerometer was connected to the data logger (SPE LoggersÒ) via a cable with an inline plug. Each farmer was instructed to firmly put the helmet on and attach the cable to the data logger when sitting on the ATV. Conversely when leaving the ATV, the cable was to be unplugged and helmet removed. In this way, the total riding time of the ATV for a workday could be determined by the accumulation of helmet vibration data episodes. Helmet mounted vibration data were also gathered for future analysis of head/neck vibration of farmers.
2. Material and methods 2.1. Participants Twelve mixed stock farmers (Table 1) were recruited from the South Otago rural population of New Zealand. South Otago is representative of the classical New Zealand rolling lowland mixed stock farm. These farmers were highly experienced, self-employed,
Table 1 Characteristics of recruited farmers (n ¼ 12 males). Variable
Min
Max
Mean
SD
Age (yrs) Height (m) Weight (kg) BMI (kg/m2) Farming experience (yrs)
41.0 1.70 75.0 22.2 15.0
62.0 1.85 110.0 32.8 44.0
49.6 1.78 90.0 28.4 29.6
7.1 0.05 9.4 2.8 8.1
531
Fig. 1. ATV with data logger mounted on the rear carrying rack.
532
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2.4. Data analysis Vibration exposure was expressed as the daily vibration dose value (VDV). The use of the VDV, as opposed to root mean square (RMS) to measure exposure, followed ISO 2631-1 recommendations as the measure is more sensitive to the amplitude peaks that are associated with shock (ISO, 1997). In order to confirm the use of the VDV as an appropriate exposure measure the maximum crest factor for the Z direction was calculated for each farmer. A mean crest factor in excess of 9.0 would justify use of the VDV as a more sensitive indicator of shock (ISO, 1997). The acceleration dose for mechanical shock was calculated in accordance with the ISO 2631-5 standard from the same ATV seat pad accelerations. The risk of adverse health effects from exposure to mechanical shock was obtained by comparing the acceleration dose with established exposure limits (ISO, 2004). Calculation of both VDV and exposure to mechanical shock are explained below. 2.5. Whole body vibration – vibration dose value (VDV) Following ISO 2631-1 recommended frequency weighting, VDVs in the X, Y, and Z orthogonal directions were calculated (Eq. (1)) as the weighted fourth power of acceleration.
2 VDVi ¼ wi 4
ZT
314 4
a ðtÞdt 5
(1)
0
where awi is the frequency-weighted acceleration with values of wX ¼ 1.4, wY ¼ 1.4, wZ ¼ 1.0 (ISO, 1997). The total VDV (tVDV) over the collection period was then calculated as the vector sum (Eq. (2)) of VDV obtained for each direction of vibration.
tVDV ¼
VDV4x þ VDV4y þ VDV4z
1 4
(2)
The VDV obtained from each participant’s 20 min data collection sample (T20) was then used to calculate a daily VDV by extrapolation to the total riding time (Ttotal) as recorded from the helmet (Eq. (3)).
VDV ¼ VDVt
1 Ttotal 4 T20
(3)
2.6. Mechanical shock – calculation of the spinal response acceleration dose
"
X
#1=6 A6ik
Dkd ¼ Dk
td tm
1=6
(5)
The daily equivalent static compression dose, Sed, was calculated by a weighted sum of the three orthogonal daily acceleration dose values where mX equals 0.015 MPa/(m/s2), mY equals 0.035 MPa/(m/ s2) and mZ equals 0.032 MPa/(m/s2) (Eq. (6)).
2 Sed
¼ 4
X
31=6 ðnk Dkd Þ
65
(6)
k ¼ x;y;z
Factor R is the ratio between the static compression dose and the ultimate strength of the lumbar spine for a person. R represents the risk of obtaining chronic injury and is used in the assessment of the adverse health effects related to the human response acceleration dose (Eq. (7)).
2 R ¼ 4
n X Sed N1=6 Sui c i¼1
!6 31=6 5
(7)
where n is the number of years of exposure; N is the number of exposure days per year; Sui is the ultimate strength of the lumbar spine adjusted for the age at which exposure starts ‘b’ and years of exposure ‘i’, with Sui (MPa) ¼ 6.75 0.966(b þ i); and ‘c’ is a constant representing the static stress due to gravitational force. A recommended value for ‘c’ is 0.25 MPa for driving posture (ISO, 2004). In accordance with the recommendations of the ISO 2631-5 the health effects for the present study are evaluated by: An Sed < 0.5 MPa indicates a low probability of adverse health effects An Sed > 0.8 MPa indicates a high probability of adverse health effects A Factor R < 0.8 indicates a low probability of adverse health effects A Factor R > 1.2 indicates a high probability of adverse health effects
2.7. Survey of seasonal ATV use and spinal pain
The collected acceleration data from the ATV seat pad was resampled at 160 Hz in accordance with the recommendations of the ISO 2631-5 standard for investigating shock. Using spinal stress methods detailed in the ISO 2631-5, lumbar spine accelerations in the X, Y and Z directions (alX, alY, alZ) were determined in response to the accelerations measured at the seat pad (ISO, 2004). The acceleration dose, Dk, in metres per second squared, for each direction was calculated as the sixth power of acceleration (Eq. (4)).
Dk ¼
workday, the average daily dose, Dkd, in metres per second squared, was calculated where td is the duration of the daily exposure, and tm is the period over which Dk has been measured (Eq. (5)).
(4)
Although the present data collection took place in winter; it is known that there are seasonal variations in ATV use with peak usage occurring during the spring lambing period in New Zealand (Knight et al., 2005). The participants were therefore surveyed with a modified version of the whole body vibration health surveillance questionnaire (WBVHSQ) developed by Pope and colleagues (Pope et al., 2002). This modified questionnaire specifically asked the farmers to estimate their typical daily seasonal (winter, spring, summer, autumn) ATV usage. The modified WBVHSQ also asked the participants whether they had suffered from low back, upper back or neck pain within the past 7 days and within the past 12 months.
i
2.8. Statistical analysis where Aik is the ith peak of the lumbar spine acceleration response alk(t) and ‘k’ corresponds to the X, Y and Z axes. For X and Y directions, both the positive and negative peaks were counted. For the z direction only the positive peaks were counted, since it is the compression forces on the spine during shocks that are of interest for exposure severity (ISO, 2004). In order to scale the dose to an average
Filtering of vibration data and calculation of all derived quantities of WBV and mechanical shock were carried out using LabView 8.0tm. The personal and demographic data, as well as the sampled and calculated daily and annual exposure to WBV (as the VDV) and mechanical shock are presented descriptively in Tables 1 and 2. For
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533
Table 2 Calculation of daily vibration dose value (VDV) and acceleration dose per axis, static compression dose, and risk factor R. Whole body vibration
Mechanical shock
Farmer
Time 20
VDVX
VDVY
VDVZ
Sum20
DRT
VDVDRT
DX
DY
DZ
DXD
DYD
DZD
Sed
D/Y
Exp.
R
1 2 3 4 5 6 7 8 9 10 11 12
18.4 29.2 25.1 26.8 26.0 14.4 22.1 20.2 26.5 18.2 22.1 25.6
9.5 5.4 13.5 9.7 8.9 6.9 11.0 9.2 8.0 6.9 9.3 6.6
7.2 5.1 14.1 10.1 8.1 6.1 11.0 7.3 7.4 7.5 7.9 8.1
11.6 7.2 14.2 11.0 8.7 6.8 11.7 8.2 9.5 8.4 10.7 7.6
13.0 8.0 18.3 13.6 11.3 8.8 14.8 11.0 11.1 10.1 12.5 9.9
45.6 125.2 196.3 117.8 40.2 68.8 83.2 13.3 56.3 122.6 190.8 88.8
16.3 11.6 30.6 19.7 12.6 13.0 20.6 9.9 13.5 16.3 21.4 13.5
5.34 2.40 7.33 5.51 4.68 4.09 6.57 4.92 4.85 3.45 4.41 3.49
3.58 2.77 6.57 4.84 4.50 3.60 6.00 3.35 3.88 4.37 4.39 4.89
9.16 3.69 9.48 6.16 4.42 4.21 8.29 4.66 5.09 4.56 8.17 4.96
6.2 3.1 10.3 7.1 5.0 5.3 8.2 4.6 5.5 4.7 6.3 4.3
4.2 3.5 9.3 6.2 4.8 4.7 7.5 3.1 4.4 6.0 6.3 6.0
10.7 4.7 13.4 7.9 4.8 5.5 10.3 4.3 5.8 6.3 11.7 6.1
0.34 0.16 0.44 0.27 0.18 0.19 0.34 0.15 0.19 0.23 0.38 0.23
250 364 364 300 325 350 300 364 350 336 350 294
42 30 25 15 22 30 28 24 33 44 34 28
0.50 0.20 0.47 0.26 0.18 0.25 0.38 0.17 0.23 0.33 0.48 0.24
Mean SD Min Max
22.9 4.4 14.4 29.2
8.7 2.2 5.4 13.5
8.3 2.4 5.1 14.1
9.6 2.2 6.8 14.2
11.9 2.8 8.0 18.3
95.7 57.3 13.3 196.3
16.6 5.8 9.9 30.6
4.75 1.36 2.40 7.33
4.40 1.09 2.77 6.57
6.07 2.11 3.69 9.48
5.89 1.94 3.06 10.33
5.50 1.74 3.12 9.26
7.61 3.10 4.35 13.36
0.26 0.10 0.15 0.44
328.9 35.9 250 364
29.6 8.1 15.0 44.0
0.31 0.12 0.17 0.50
Key – Whole body vibration: Time 20 ¼ approximately 20-min riding sample; VDVX, VDVY and VDVZ ¼ 20-min vibration dose values in X, Y and Z directions (m/sec1.75); Sum20 ¼ Vector summation of X þ Y þ Z; DRT ¼ daily riding time (in min); VDVDRT ¼ calculated daily VDV (m/sec1.75). Key – Mechanical shock: DX, DY, and DZ ¼ 20-min acceleration dose (m/sec2) in X, Y and Z directions; DXD, DYD, and DZD ¼ Daily acceleration dose (m/sec2) in X, Y and Z directions; Sed ¼ Daily equivalent static compression doses in MPa; D/Y ¼ Days of exposure per year; Exp. ¼ Years of experience; R ¼ Factor R.
the purposes of determining a predicted seasonal daily VDV exposure a mean ratio between estimated ATV usage in winter and actual ATV usage from the helmet mounted accelerometer was calculated, and applied to the WBVHSQ survey to estimate exposure for spring lambing, spring other than lambing, summer and autumn. These survey data thus allowed the estimation of seasonal daily ATV riding time and seasonal VDV exposure as well as the total days per week and days per year of ATV use; information that was required for calculating working lifetime exposure for mechanical shock (Factor R). The presentation of these daily and yearly WBV and shock exposure calculations allows a comparison to the ISO 2631-1 and ISO 2631-5 AL and MPL for adverse health effects amongst New Zealand farmers. 3. Results 3.1. Vibration dose value (VDV) Each farmer rode their ATV for a mean of 22.9 min (Table 2). The crest factor in the Z direction had a mean score of 9.5 within a range of 7.8–11.9 exceeding the recommended threshold exposure for the use of the VDV. The filtered and weighted vibration data for this time period produced similar X, Y and Z mean VDV scores of 8.7, 8.3 and 9.6 m/sec1.75, respectively and were vector summated (ISO 2631-1 guideline) for a resultant VDV of 11.9 m/sec1.75. Each of these calculated time/dose VDV samples were then extrapolated to the full day riding time per day (mean 95.7 min) to obtain an estimated mean daily VDV of 16.6 m/sec1.75 (Table 2). The 95.7 min vector summated VDV of 16.6 m/sec1.75 was then entered into the VDV equation to calculate a VDV AL (9.1 m/sec1.75) and MPL (21.0 m/sec1.75) would be reached after 8.0 min and 220.8 min respectively of ATV use for these farmers under these conditions. All 12 farmers had estimated daily VDV scores (DRT Sum – Table 2) that exceeded the AL with two farmers (Farmer 3 & 11 – Table 2) exceeding the MPL. 3.2. Mechanical shock exposure
22.9-min riding sample. The Sed score of each farmer was then extrapolated to their full day riding time giving a mean daily Sed of 0.26 MPa (Table 2). This value represents a low probability of an adverse health effect (Sed < 0.5 MPa) in terms of ISO 2631-5. Based on Table 2, farmers rode their ATV for a mean of 328.9 days per year. The age at which the exposure to shocks started was estimated by subtracting years of experience from current age. A mean factor R was then calculated for each farmer (mean 0.3) with no farmers demonstrating a score approaching 0.8, the lower limit of the ISO 2631-5 recommendations. 3.3. Spinal pain survey Low back pain was the most commonly reported complaint for both 7-day (50%) and 12-month prevalence (67%), followed by the neck (17% and 42%) and the upper back (17% and 25%), respectively (Table 3). 3.4. Seasonal variation The recorded winter season ATV daily riding time (mean of 95.7 min) was compared to the farmer estimated winter season use (mean of 156.0 min) extracted from the WBVHSQ (Table 4). These data were used to calculate a ratio of 0.62 between recorded and farmer estimated ATV exposure which was then applied to all farmer estimated seasonal daily riding times. Thus a farmer using an ATV during summer was calculated as having a mean vibration exposure time of 138.0 min, in autumn 114.0 min, in winter 95.7 min (recorded), in spring (non-lambing) 192.0 min and in spring lambing 318.0 min.
Table 3 Seven day and 12 month prevalence of back and neck pain. LBP 7 Pain Yes (n¼) Pain No (n¼) Percent Yes
The seat pad measured accelerations yielded mean acceleration dose values of 4.75, 4.40 and 6.07 m/s2 for the X, Y and Z direction respectively, with a resultant mean Sed value of 0.20 MPa for the
LBP 12
UBP 7
UBP 12
CxP 7
CxP 12
6 6
8 4
2 10
3 9
2 10
5 7
50
67
17
25
17
42
Key: LBP 7, Low back pain in past 7 days; LBP 12, Low back pain in past 12 months; UBP 7, Upper back pain in past 7 days; UBP 12, Upper back pain in past 12 months; CxP 7, Neck pain in past 7 days; CxP 12, Neck pain in past 12 months.
534
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Table 4 Seasonal, weekly and daily use of ATV in a sample of New Zealand sheep farmers (mean SD). Season
DPW
DRT Est
Spring lambing Spring non-lambing Summer Autumn Winter
7.0 6.6 5.6 5.5 6.7
510.0 312.0 222.0 180.0 156.0
(0.0) (0.7) (1.1) (1.1) (0.7)
(144.0)b (156.0)b (126.0)b (126.0)b (72.0)b
DRT 318.0 192.0 138.0 114.0 95.7
(90.0)c (96.0)c (78.0)c (78.0)c (57.3)a
Key – Note: Duration of lambing was 34.3 7.5 days; DPW Farmer estimated days per week of ATV usage; DRT Est Farmer estimated ATV daily riding time in minutes; DRT Actual and calculated daily riding time in minutes. a Actual daily riding time measured from helmet accelerometer. b Estimated daily riding time from survey data. c Calculated seasonal daily riding time.
In terms of survey 50% (n ¼ 6) of these farmers experienced low back pain during the past 7 days and 67% (n ¼ 8) during the past 12 months. Although only 12 farmers were surveyed, this is consistent with the high prevalence of low back pain and musculoskeletal disorders observed in occupations using ATVs (Firth et al., 2002; Rehn et al., 2002; Walker-Bone and Palmer, 2002). As the shock doses for these farmers were low, it is more likely that the high doses of WBV, and not shock are the risk factor for the development of low back pain. Other factors such as the sustained flexed and seated postures used while driving the ATV, and frequent heavylifting work tasks associated with farming and often taken in series with ATV riding, are also likely to account for the high prevalence of low back pain among farmers. 4.1. Limitations
4. Discussion The mean daily VDV sum exposure for farmers using ATVs is high (16.6 m/sec1.75), exceeding the ISO recommended AL (9.1 m/ sec1.75) after 8.0 min and exceeding the recommended MPL (21.0 m/sec1.75) after 220.8 min. The 12 month prevalence of LBP was also high and similar to that of New Zealand farmers previously recorded by Firth et al. (2002). Twelve month prevalence of neck pain at 42% is also high supporting previous research on ATV WBV vibration exposures in Sweden (Rehn et al., 2002). Despite such high levels of vibration exposure, the risk exposure from mechanical shock was shown to be low. If the calculations for seasonally adjusted ATV riding time hold true we would expect that these farmers exceed the calculated MPL (220.8 min) during the spring lambing season (approximately 34 days) placing them at a high risk of developing vibration induced low back pain. All calculations for VDV exposures also demonstrate that these farmers consistently exceeded the AL during the sampled day. It is likely that farmers exceeded the AL on typical farm work days during each season by a considerable amount, placing them at some risk of WBV induced low back pain. Paradoxically participants were not exposed to shock in terms of doses exceeding the Sed lower limit of 0.5 MPa, or lifetime exposure of 0.8 for risk factor R, indicating a low probability of adverse health effects from ATV induced shock exposure associated with farming. Furthermore, factor R ranged from 0.20 to 0.50 demonstrating a low shock exposure from ATV use, particularly where some of these participants had been farming for at least 40 years. However, the calculations for Factor R are reliant on using this recorded VDV exposure as a constant throughout the work year and over working lifetime. We did not record day to day variations in vibration exposure for these farmers and it is also likely that considerable seasonal and yearly variations occur. Over time, these unknown factors are likely to have a summative effect on cumulative shock loadings expressed as Sed and Factor R and as such, our results could either over or underestimate cumulative shock exposure. Although a number of studies have suggested that exposure to severe shock events can occur with WBV exposure (Hoy et al., 2005; Johanning et al., 2006; Okunribido et al., 2006a, 2007; Rehn et al., 2005), these authors have not used the recommended ISO 2631-5 standard to investigate the adverse health effects associated with shock (Alem, 2005). To our knowledge, only two studies have investigated the influence of shock on humans. Burstrom et al. (2006) used the ISO 2631-5 standard to investigate shock doses to aircraft cabin attendants during aircraft landing. Khorshid et al. (2007) measured WBV and shocks in motor vehicles crossing different speed control humps during urban driving. As there is no published shock exposure measurements from agricultural vehicle use comparisons cannot be made. It will require further research with a larger sample of farmers to verify these results.
It is possible that a 20-min riding sample is a poor representation of the true WBV and shock exposure for these farmers during a regular workday and may not represent the true risk of adverse health effects from ATV use. The relatively large uncertainty of WBV measurements reflecting true daily WBV exposure (15–40% variability), has been recently investigated (Pinto and Stacchini, 2006) and may be a factor in determining the true risk of adverse health effects. Although we tested experienced farmers, due to the small sample size it is also difficult to generalize the findings to all farmers who drive ATVs. We also did not quantify the postures employed by these farmers when sitting on the ATVs. Although variations in seated posture will likely have an effect on vibration exposure and transmissibility, neither ISO 2631-1 nor 2631-5 currently address the potential effects of such posture. While the farmers were asked to drive their ATV on a typical farm route on their own farm, it may be that they chose a path that was of relatively even terrain and familiar to them. Participation in the study might have also made them more cautious than normal, thereby not travelling at speeds that they would on a normal workday. Although this 20-min riding sample may be representative of different surface induced WBV, the shock dosage may be less than that of a regular workday when farmers are driving on more uneven terrain, and undertaking everyday farming tasks. If this assertion holds true, the results from this study will underestimate total exposure to mechanical shock from ATV use in farmers. 5. Conclusion The present findings indicate farmers are exposed to very high levels of WBV during daily use of an ATV, and particularly during the busy spring lambing season. This exposure in combination with a constrained seated posture and physically demanding work tasks is likely to be a substantial risk factor for the development of occupational low back pain, at least in this sample of New Zealand farmers. Although mean daily Sed value appeared to be within safe limits at 0.26 MPa the data for this measure also demonstrated considerable variability amongst the 12 farmers (0.15–0.44 MPa) indicating that a larger sample over a greater length of time might be required to calculate this factor with any confidence. The calculation of a working lifetime risk factor R of 0.31 is also well below the ISO 2631-5 recommended lower limit of 0.5 and 0.8 respectively, generally indicating a low probability of adverse health effects from ATV induced mechanical shock exposure. Acknowledgements We thank Scott Parsons and Steve Slack, electronics engineers from Scott Parsons Electronics (SPELEC) in Albany, Western
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