Biomechanics of leaning forward against a support with an extreme standing reach

Abstract

Back discomfort, lower extremity loading and unbalanced positions may inhibit workers from standing for industrial stationary work. Two forward-leaning supports were compared to unsupported standing during an extreme reach with 30° trunk flexion under varied light load conditions in the outstretched hands. A total of 11 males from the university participated (mean age 30 years [SD =  5]). Link segment modelling showed a 25–30% reduction in the L4/L5 bilateral hip external moments when using a chest-height support. Ribcage expansion with maximal inspiration remained unchanged with an average 85 N of compression force, and low back discomfort remained tolerable for this difficult reach. Leaning against a work table had no influence on L4/L5 moments or back discomfort because contact was at the pelvis; the external moment at the hips decreased by 6%. Postural stability was improved with little migration of the centre of pressure under both supports. Only the chest support showed potential to influence work positioning and prevent back injuries; further study is needed on support forces and usability.

Abstract

Practitioner summary: Forward leaning stabilised an extreme, standing reach; the table reduced the single hip moment by only 3%. A chest-leaning support reduced the moment at L4/L5 by 25–30% and the hip by 12–15%; moreover, back discomfort remained tolerable and chest expansion was unchanged with an average 85 N of compression.

Keywords::

• health-care ergonomics
• industrial ergonomics
• equipment design
• biomechanics
• product design