All subjects were studied twice and the use of ergonomic low back support was randomised. All driving sessions were performed by two similar busses (Kabus) with similar seats and automatic transmission.
The low back support (Ikonen Matti Oy, Imatra, Finland) was ergonomically shaped, air filled and tied to the seat by sticker belt. The thickness of the support was freely adjustable by pump and valve. All drivers were allowed to choose freely the thickness of the support before driving.
Questionnaires on low back and neck–shoulder pain inten- sities and subjective perception of fatigue were assessed by visual analogue scales (100 mm VAS [29]). Every subject evaluated his/her back and neck–shoulder pain, and fatigue intensities on a 100-mm where 0 denoted no pain or fatigue at all, and 100 the worst possible pain or fatigue. The result was given in millimetres. Low back pain induced disability was assessed by Oswestry disability index (ODI 0–100 [30]). The additional questionnaires for pain and fatigue intensities were filled before and after every driving session. Questionnaire included also pain during driving and a question whether the drivers benefited of the low back support or not.