Table 9
Low back and neck–shoulder pain and fatigue (VAS) in urban bus drivers before and after driving in drivers having recurrent low back pain (low back support vs. no support, n = 24)
Vibration positive (n = 12) Vibration negative (n = 12)
Baseline After driving Baseline After driving
Low back pain (0–100 mm)
No support
Support 14.3 ± 24.9
15.5 ± 22.4 20.6 ± 26.6
18.8 ± 19.2 25.7 ± 29.7
27.2 ± 26.7 25.3 ± 24.1
21.8 ± 23.1
Low back fatigue (0–100 mm)
No support Support 12.4 ± 20.3
7.9 ± 8.2 29.8 ± 23.2*
29.9 ± 17.4†
19.8 ± 19.6
22.3 ± 19.6 25.9 ± 26.9
30.2 ± 29.2
Neck–shoulder pain (0–100 mm)
No support Support 12.1 ± 22.6
11.6 ± 22.1 18.7 ± 26.2
24.2 ± 22.4*
24.3 ± 21.8
22.7 ± 29.1 20.9 ± 26.1
16.9 ± 21.2
Neck–shoulder fatigue (0–100 mm)
No support 13.1 ± 21.3 25.5 ± 21.0†
22.3 ± 27.2 22.4 ± 21.0
Support 10.4 ± 13.1 32.2 ± 18.0†
20.2 ± 18.4 22.3 ± 23.3
Values are expressed as mean ± S.D.
* P < 0.05.
† P < 0.01.
found in five subjects having positive pain provocation and in four subjects with negative pain provocation.
4. Discussion
To our knowledge, there is no previous field study on low back and neck–shoulder muscle loading in urban bus drivers. Subjects of this study represented average Finnish bus drivers, and only seven out of 40 drivers had never experienced back pain. This study showed that average paraspinal muscle load- ing in urban bus drivers during driving itself was minimal. Even average muscle activity during breaks was significantly higher. Low back pain and ergonomic lumbar support had no effect on paraspinal muscle activity. Trapezius muscle activ- ity tended to be higher in drivers with LBP. Increased muscle activity was expected in drivers suffering low back pain due to protective muscle spasm or decreased due to reflex- inhibition or adaptation [35] but this was not seen during driving.
There seems to be considerable individual variation both in paraspinal and trapezius muscle activity according to the wide standard deviations in the mean values of the muscle activities. The left trapezius muscle activity varied from 1 to 12% of MVC and in right side from less than 1% to over 7% of MVC. The average paraspinal muscle activity varied from nearly 0% to over 3% of MVC between subjects of both groups. It was difficult to estimate how largely the muscle loading consists of dynamic and how largely of static load.
The low paraspinal muscle loading would suggest to pre- vent fatigue. Apparently, however, the insufficient active sta- bilisation leads to the remarkable loading of spinal column especially of intervertebral discs and also the muscle spindle activation remains question. When sitting the lumbar spine is continuously in neutral zone when the stabilising function of
muscles is more important than that of ligaments and tendons [36–38]. The continuous loading of passive elements leads to increased stress and fatigue, expose to injury and eventually even pain.
When the most important muscles stabilising back are mainly passive during driving, the importance of passive sta- bilising structures and also the significance of other stabilisers of back such as abdominal muscles must be emphasised. The disturbed function of abdominal muscles can be associated with low back pain and may expose to injury [35,39]. Since the stabilising muscles are passive during driving, the lumbar spine is supported poorly and exposed to the effect of whole body vibration and injuries caused by sudden loads [9,28].
Ergonomic low back support maintains back in physi- ologic posture when the pressure is concentrated on discs regularly. Disc pressure and myoelectric activity has been observed to decrease when the backrest inclination was increased and the low back support was used [25]. Thus, ergonomic lumbar support may prevent LBP. This is sup- ported by the subjective beneficial effect.
Overload of spine exposes to microinjuries such as inter- nal annular ruptures, which can lead even to total annular rupture and disc herniation. Internal annular ruptures cause pain, which can be diagnosed by discographic pain provo- cation. This pain can be provoked non-invasively by bony vibration test [32,34,40,41]. According to this study there was evidence for internal disc disruption being one potential cause of low back pain in bus drivers. The prevalence of inter- nal disc disruption in bus drivers suffering from recurrent low back pain was approximately the same as find earlier by disco- graphic pain provocation [42]. Low back and neck–shoulder pain and fatigue increased more during driving in drivers who had positive vibration pain provocation test than those who had negative indicating that driving may expose for pain in those cases.
The “hypersensitivity” to bony vibration must also be taken into consideration. The partial disagreement between MRI and pain provocation findings could be explained by the facts that all internal disc disruption are not visible in MRI and that all disc disruptions are not painful and the total annular rupture is not necessarily painful by the vibration stimulation test.
Trapezius muscle loading during driving seems to be remarkably higher than paraspinal muscle loading in low back. It can be associated with neck–shoulder fatigue, which increased significantly in both groups and perhaps also with pain since as low as less than 1–2% MVC is recommended in sedentary work [43]. Muscle blood flow is related to neck–shoulder pain [44] and maybe a potential link between pain and muscle loading as well as muscle spindle excitabil- ity. However, the side difference in trapezius muscle was not associated with the location of pain in pain maps and the neck–shoulder pain did not increase significantly during driv- ing. The increased left trapezius activity is probably due to that drivers mainly use their left hand in steering the bus and also by the EKG interference seen in some cases despite the filtering.
In conclusion the paraspinal muscle loading in urban bus drivers was very small and neither low back pain nor ergonomic low back support had an effect on it, however, trapezius muscle seems to be less active in drivers suffering from recurrent low back pain. Internal disc disruptions may expose to pain and fatigability during driving.
Acknowledgements
We would acknowledge Koiviston Auto Oy for financial support of this study and Kuopion Liikenne for making this study possible, Matti Ikonen for the ergonomic low back supports used in this study and Matti Suhonen MD for the observation of MRI.
Table 9
Low back and neck–shoulder pain and fatigue (VAS) in urban bus drivers before and after driving in drivers having recurrent low back pain (low back support vs. no support, n = 24)
Vibration positive (n = 12) Vibration negative (n = 12)
Baseline After driving Baseline After driving
Low back pain (0–100 mm)
No support
Support 14.3 ± 24.9
15.5 ± 22.4 20.6 ± 26.6
18.8 ± 19.2 25.7 ± 29.7
27.2 ± 26.7 25.3 ± 24.1
21.8 ± 23.1
Low back fatigue (0–100 mm)
No support Support 12.4 ± 20.3
7.9 ± 8.2 29.8 ± 23.2*
29.9 ± 17.4†
19.8 ± 19.6
22.3 ± 19.6 25.9 ± 26.9
30.2 ± 29.2
Neck–shoulder pain (0–100 mm)
No support Support 12.1 ± 22.6
11.6 ± 22.1 18.7 ± 26.2
24.2 ± 22.4*
24.3 ± 21.8
22.7 ± 29.1 20.9 ± 26.1
16.9 ± 21.2
Neck–shoulder fatigue (0–100 mm)
No support 13.1 ± 21.3 25.5 ± 21.0†
22.3 ± 27.2 22.4 ± 21.0
Support 10.4 ± 13.1 32.2 ± 18.0†
20.2 ± 18.4 22.3 ± 23.3
Values are expressed as mean ± S.D.
* P < 0.05.
† P < 0.01.
found in five subjects having positive pain provocation and in four subjects with negative pain provocation.
4. Discussion
To our knowledge, there is no previous field study on low back and neck–shoulder muscle loading in urban bus drivers. Subjects of this study represented average Finnish bus drivers, and only seven out of 40 drivers had never experienced back pain. This study showed that average paraspinal muscle load- ing in urban bus drivers during driving itself was minimal. Even average muscle activity during breaks was significantly higher. Low back pain and ergonomic lumbar support had no effect on paraspinal muscle activity. Trapezius muscle activ- ity tended to be higher in drivers with LBP. Increased muscle activity was expected in drivers suffering low back pain due to protective muscle spasm or decreased due to reflex- inhibition or adaptation [35] but this was not seen during driving.
There seems to be considerable individual variation both in paraspinal and trapezius muscle activity according to the wide standard deviations in the mean values of the muscle activities. The left trapezius muscle activity varied from 1 to 12% of MVC and in right side from less than 1% to over 7% of MVC. The average paraspinal muscle activity varied from nearly 0% to over 3% of MVC between subjects of both groups. It was difficult to estimate how largely the muscle loading consists of dynamic and how largely of static load.
The low paraspinal muscle loading would suggest to pre- vent fatigue. Apparently, however, the insufficient active sta- bilisation leads to the remarkable loading of spinal column especially of intervertebral discs and also the muscle spindle activation remains question. When sitting the lumbar spine is continuously in neutral zone when the stabilising function of
muscles is more important than that of ligaments and tendons [36–38]. The continuous loading of passive elements leads to increased stress and fatigue, expose to injury and eventually even pain.
When the most important muscles stabilising back are mainly passive during driving, the importance of passive sta- bilising structures and also the significance of other stabilisers of back such as abdominal muscles must be emphasised. The disturbed function of abdominal muscles can be associated with low back pain and may expose to injury [35,39]. Since the stabilising muscles are passive during driving, the lumbar spine is supported poorly and exposed to the effect of whole body vibration and injuries caused by sudden loads [9,28].
Ergonomic low back support maintains back in physi- ologic posture when the pressure is concentrated on discs regularly. Disc pressure and myoelectric activity has been observed to decrease when the backrest inclination was increased and the low back support was used [25]. Thus, ergonomic lumbar support may prevent LBP. This is sup- ported by the subjective beneficial effect.
Overload of spine exposes to microinjuries such as inter- nal annular ruptures, which can lead even to total annular rupture and disc herniation. Internal annular ruptures cause pain, which can be diagnosed by discographic pain provo- cation. This pain can be provoked non-invasively by bony vibration test [32,34,40,41]. According to this study there was evidence for internal disc disruption being one potential cause of low back pain in bus drivers. The prevalence of inter- nal disc disruption in bus drivers suffering from recurrent low back pain was approximately the same as find earlier by disco- graphic pain provocation [42]. Low back and neck–shoulder pain and fatigue increased more during driving in drivers who had positive vibration pain provocation test than those who had negative indicating that driving may expose for pain in those cases.
The “hypersensitivity” to bony vibration must also be taken into consideration. The partial disagreement between MRI and pain provocation findings could be explained by the facts that all internal disc disruption are not visible in MRI and that all disc disruptions are not painful and the total annular rupture is not necessarily painful by the vibration stimulation test.
Trapezius muscle loading during driving seems to be remarkably higher than paraspinal muscle loading in low back. It can be associated with neck–shoulder fatigue, which increased significantly in both groups and perhaps also with pain since as low as less than 1–2% MVC is recommended in sedentary work [43]. Muscle blood flow is related to neck–shoulder pain [44] and maybe a potential link between pain and muscle loading as well as muscle spindle excitabil- ity. However, the side difference in trapezius muscle was not associated with the location of pain in pain maps and the neck–shoulder pain did not increase significantly during driv- ing. The increased left trapezius activity is probably due to that drivers mainly use their left hand in steering the bus and also by the EKG interference seen in some cases despite the filtering.
In conclusion the paraspinal muscle loading in urban bus drivers was very small and neither low back pain nor ergonomic low back support had an effect on it, however, trapezius muscle seems to be less active in drivers suffering from recurrent low back pain. Internal disc disruptions may expose to pain and fatigability during driving.
Acknowledgements
We would acknowledge Koiviston Auto Oy for financial support of this study and Kuopion Liikenne for making this study possible, Matti Ikonen for the ergonomic low back supports used in this study and Matti Suhonen MD for the observation of MRI.
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