## 4 Discussion
(2018) [2] suggested that inappropriate postures, together with vibration, would amplify exposure to WBV. Therefore, it is important to consider that although posture alone may or may not affect the lower back, the addition of vibration can help trigger lower back symptoms. Psychological factors are poorly reported in the studies and may have a direct or indirect relationship with mechanical vibration and other factors for lumbar symptoms. [PERSON] et al. (2007) [31] reported a significant association between negative moods andLBP caused by a high level of stress, since bus drivers must meet schedules, provide good service to passengers, adhere to safe driving practices, and withstand peak traffic conditions. In other studies, [PERSON] et al. (2010) [34] stated that stressful and psychosocial ergonomic factors, as well as a lack of a sports activity, are associated with LBP in professional urban bus drivers. Similarly, [PERSON] et al. (2002) [19] suggested that psychosocial factors can influence disability and LBP. Among the included publications, [PERSON] and [PERSON] (1992) [29]; [PERSON] et al. (2007) [31]; [PERSON] et al. (2007) [32]; and [PERSON] et al. (2018) [2] used questionnaires to assess the drivers' routine. Among the factors reported as the cause of LBP, it was suggested that fatigue can be caused by the mechanical vibration received throughout the daily work routine. [PERSON] et al. (2007) [31] reported a significant relationship between fatigue and LBP, as did [PERSON] et al. (2007) [15], who found that exposure to vibration can induce fatigue and depletion of the paravertebral muscles of the lumbar region. In addition and agreement, [PERSON] and [PERSON] (1992) [29] performed electromyographic measurements of the back muscles during the vertical vibration felt by the drivers, and observed that the increased muscle tension increases the load on the vertebral bodies and discs, causing fatigue and pain. Moreover, it was reported that vibration-induced muscle fatigue has a conditioning effect, resulting in increased susceptibility of the spine to injury. [PERSON] and [PERSON] (1992) [29] concluded that there is a significant indicator of lumbar problems between exposure to WBV and bus drivers, which corroborates the studies by [PERSON] and [PERSON] (1998) [10] and [PERSON] et al. (2007) [15]. [PERSON] et al. (2018) [2] and [PERSON] et al. (2015) [7] described several causes of LBP, such as speed, vehicle design, and environmental conditions. [PERSON] et al. (2013) [30] and [PERSON] et al. (2007) [31] reported that the body posture of the driver was also one of the causes that influenced the transmissibility of the vibration. [PERSON] et al. (2015) [13] reported that evidenced nervous system disorders indicate the need to undertake preventive measures tailored for bus drivers. [PERSON] et al. (2019) [35] described worse health, mainly common mental disorders, was associated with self-assessed work precariousness as reported by bus drivers and conductors. LBP has been also found in taxi drivers (prevalence of 27.9%) through self-reported LBP in the past 12 months. [PERSON] et al. (2019) [36] interviewed 400 truck drivers to assess the magnitude of LBP in these individuals and a prevalence of 65% was found. [PERSON] et al. (2020) [37] studied the impact of rest breaks and stretching exercises on commercial truck drivers, and reported that these individuals presented a reduction in LBP and disability due to the use of supplementary exercises during break periods. Regarding the limitations of this systematic review, different methods were used for the evaluation of mechanical vibration exposition, only four databases were used, only publications in English were considered, and different types of vehicles and designs were observed. Furthermore, control groups were not included in the five studies, and X-rays of the lumbar spine were not assessed. Consequently, according to the overall RoB judgment, the articles included in this review were, in general, at a serious risk of bias.