Purpose: Research has shown that there are some risk factors for creating and developing low back pain with prolonged standing. For attempt to recognition of predisposing factors to development of LBP during prolonged standing, the purpose of this study was to investigate to maximal voluntary contraction (MVC) at selected groups of muscles and some of the psychological aspects in back-healthy subjects who developed LBP during prolonged standing.Methods: In this cross sectional study, 25 back-healthy subjects and 14 chronic nonspecific LBP completed anxiety inventory (STAI), Tampa Scale for kinesiophobia (TSK) and pain catastrophizing scale (PCS) questionnaires. Dynamometer was used to assess MVC of the selected groups of muscles. Finally back-healthy subjects get tested for 2 h prolonged standing protocol and based on a visual analog scale (VAS) were categorized as pain developers (PD) or non-pain developers (NPD).Results: Ten subjects (% 40) with developing pain were categorized as PD. There were no significant difference at psychological aspects between three groups of PD, NPD and LBP had. But analysis of MVC showed PD and LBP groups had less MVC at the left plantar flexors than left plantar flexors of the NPD group. Also PD and LBP groups had significantly more between two sides asymmetry at MVC at the plantar flexors compared to NPD group.Conclusion: This preliminary data suggests less MVC and asymmetry of MVC at plantar flexor muscles maybe related to development of the LBP during prolonged standing in the back-healthy peoples. Future study is needed to investigate other function of plantar flexors and their probably relations to development of LBP during prolonged standing
