Effects of relative hand location upon movement time and fatigue

Details

• Personal Author:
  Wiker, S. F.
• Description:
  Workers often perform manual assembly tasks while hands are postured above the shoulders or to the side of the body. The consequences of such work postures, in terms of decrements in movement performance capability and onset of fatigue symptomatology were unclear. Previous studies of work height upon psychomotor performance capabilities did not examine the consequences of locating working hands above shoulder level or to the side of the body, and failed to consider a wide range of hand loads, work:rest ratios, or sustained work periods. Experiments were conducted to study the sensitivity of movement performance, as well as onset and severity of localized muscle fatigue (LMF) in the shoulder, to a wide range of hand locations about the shoulder under various hand loads, ratios of work-to-rest, and task durations. Subjects performed a spatially-constrained stylus-to-hole Fitts reciprocal movement task designed to simulate high-speed manual assembly operations while providing basic information regarding changes in human move and positioning capabilities. Following movement trials subjects provided cross-modal self-reports of overall and regionalized fatigue or discomfort. In a latter experiment self-reports were augmented with objective metrics of LMF (e.g. surface electromyographic recordings and arm tremor). Movement performance degraded when subjects worked with hands postured above shoulder level. Move and positioning times increased 15.3 and 26.5 percent respectively with elevation of the hand from -15 to 60 degrees respective to shoulder level. LMF increased markedly following movement trials with hands postured above shoulder level; particularly when hand loads and work:rest ratios were increased. Overhead work produced significant LMF despite postural exertion levels below currently recommended limits. Locating hands to the side of the body, or differences in isometric strength capability found between arm postures, were not responsible for LMF or performance decrements found. Decrements in overhead movement performance were attributed to reductions in steering muscle efficiencies, and to LMF resulting from hydrostatic and intramuscular tension restrictions to circulatory feed of the elevated arm. Equations are provided for prediction of move and positioning performance when hands are postured above the shoulders. Workplace design and methods recommendations are provided for job designers facing work height decisions in manual assembly environments. [Description provided by NIOSH]
• Subjects:
  Cumulative Trauma Disorders Ergonomics Fatigue Musculoskeletal Diseases Musculoskeletal System Occupational Health Safety
• Keywords:
  Arm-injuries Cumulative-trauma Cumulative-trauma-disorders Musculoskeletal-system Musculoskeletal-system-disorders Repetitive-work Work-analysis
• Publisher:
  University of Michigan
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Dissertation
• Place as Subject:
  Michigan ; OSHA Region 5
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-254
• NIOSHTIC Number:
  nn:20046453
• Citation:
  Ann Arbor, MI: University of Michigan, 1986 Jan; :1-254
• Federal Fiscal Year:
  1986
• Performing Organization:
  University of Michigan at Ann Arbor, Ann Arbor, Michigan
• Peer Reviewed:
  False
• Start Date:
  19820701
• Source Full Name:
  Effects of relative hand location upon movement time and fatigue
• End Date:
  19950630
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:e6c4579d620e7b0c4ce5a562f303588302c8a718b222145c5e10d71d8692ed24371318f47e7bc82a37782988034fa58cac94d316d396cf2aacc57654897643f6
• Download URL:
  https://stacks.cdc.gov/view/cdc/201508/cdc_201508_DS1.pdf
• File Type:
  [PDF - 7.69 MB ]