Background: Prolonged sitting posture as in computer users is harmful to the spine and may lead to posture abnormalities, which are due to changes in spinal mobility, leading to changes of back functional stability and mobility. Purpose: to investigate the effect of prolonged sitting posture on lumbar range of motion (LROM) in computer users. Material and methods: thirty-two adult computer users of both sexes participated in this study. Their age ranged from 20 to 35 years, with no musculoskeletal diseases or current spinal pain. Group A: "16" participants were using computer from 8 to 10 years, divided into: A1: 8 participants were using computer more than 5 hours daily. A2: 8 participants were using computer from 2 to 5 hours daily. Group B: "16" participants were using computer from 2 to 4 years, divided into: B1: 8 participants were using computer more than 5 hours daily. B2: 8 participants were using computer from 2 to 5 hours daily. Back range of motion device (BROM II) was used to evaluate LROM. Results: Two-way MANOVA was conducted to investigate the effect of years and daily hours of computer usage on all lumbar range of motion. Two-way MANOVA showed a significant effect of years of computer usage on lumbar flexion, extension, right lateral flexion, left lateral flexion and left rotation ROM. A significant effect of daily hours of computer usage was found on lumbar extension ROM, while there was no significant effect of daily hours of
computer usage on other ROM measurements. There was no significant interaction effect of years and daily hours of computer usage on lumbar flexion (p = 0.24), extension (p = 0.26), right lateral flexion (p = 0.73), left lateral flexion (p = 0.54), right rotation (p = 0.61) and left rotation ROM (p = 0.1). Conclusion: the effect of prolonged sitting posture on LROM in computer users varies according to the daily hours and number of years of computer usage.