title: A study of the difference between nominal and actual hand forces in two-handed sagittal plane whole-body exertions.
abstract: Given a task posture, changes in hand force magnitude and direction with regard to joint locations result in variations in joint loads. Previous work has quantified considerable vertical force components during push/pull exertions. The objective of this work was to quantify and statistically model actual hand forces in two-hand, standing exertions relative to the required nominal horizontal and vertical hand forces for a population of widely varying stature and strength. A total of 19 participants exerted force on a fixed handle while receiving visual feedback on the magnitude of force exerted in the required horizontal or vertical direction. A set of regression equations with adjusted R(2) values ranging from 0.20 to 0.66 were developed to define actual hand force vectors by predicting off-axis forces from the required hand force magnitude. Off-axis forces significantly increase the overall magnitude of force exerted in two-hand push/pull and up/down standing force exertions. STATEMENT OF RELEVANCE: This study quantifies and statistically models actual hand forces in two-hand, standing exertions. Inaccuracies in hand force estimates affect the ability to accurately assess task-oriented strength capability. Knowledge of the relationship between nominal and actual hand forces can be used to improve existing ergonomic analysis tools, including biomechanical simulations of manual tasks.
authors.affiliation: University of Michigan Transportation Research Institute, Ann Arbor, MI, USA. grovess@umich.edu
authors.forename: Suzanne G
authors.initials: SG
authors.lastname: Hoffman
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Reed
authors.forename: Don B
authors.initials: DB
authors.lastname: Chaffin
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D006804:Ergonomics / Q000295:instrumentation / Q000379:methods; D025461:Feedback, Physiological; D005260:Female; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D008297:Male; D005082:Physical Exertion / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D055815:Young Adult