Lectures 29: Work and Rest

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Lectures 29 Work and Rest
Readings Chapanis (1996, chapter 5)
09/10/99
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Goals

• Introduce methods for scheduling rest breaks
  according to physical workload, and for designing
  patterns of shift work

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Introduction Two Kinds of Work

• Physical Work
• e.g., work on automobile assembly line,
  construction, mining
• stresses are primarily physical
• 2) Mental Work
• E.g., air traffic controller
• stresses are primarily mental

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Energy Cost of Work
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Grades of Physical Work
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Recommended Limits

• Energy Expenditure (kcal/min, average)
• 8-hour shift 4-hour shift
• Male lt 5.00 lt 6.25
• Female lt 3.35 lt 4.20
• (lt 1/3 MAP)
• Heart Rate (beats/min, average)
• Arm work lt 99
• Leg work lt 112

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Rest Requirements

• R rest time
• T total working time
• K work metabolic rate
• S standard metabolic rate

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Rest Requirements Example 1

• T 60 min
• K 6 kcal/min
• S 4 kcal/min

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Rest Requirements Example 2

• T 60 min
• K 10 kcal/min
• S 4 kcal/min

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Biological Rhythms

• A complicating factor in all decisions about work
  and rest cycles are cyclic changes that we all go
  through in our physiological and psychological
  states.

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Cycles affecting physiology and psychology
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Cycles Govern Human Activity from Cradle to Grave

• The number of deaths due to heart disease is
  highest during the morning hours, as is the
  number of human births

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More Cycles Brainwaves during Sleep

• Beta, above 15 Hz
• fast low amplitude waves occur when cerebrum is
  alert or anxious
• Alpha, between 8 and 11 Hz
• during relaxed wakefulness
• Theta, between 3.5 and 7.5 Hz
• associated with drowsiness and light sleep
• Theta, under 3.5 Hz
• slow waves of large amplitude, often over 100
  microvolts, tend to occur in deep sleep.

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The Circadian Rhythm
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Shift Work

• Shift work is any work period starts at a time
  other than between 700 and 900 a.m.
• A quarter of the American labor force is engaged
  in shift work.

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Factors to consider in designing Shift Schedules

• Job-performance capabilities of operators at
  different times
• Physiological effects of night work on sleep and
  diet
• Psychological effects of evening and night work
  on families and friends

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Piloting Operations

• The job of piloting ships between Baltimore and
  Cape Henry.
• At the time of study, the middle 50 of trips
  took between 9.5 to 12 hours.

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Example Pilot Schedule
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Shift Examples
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Recommendations I

• Job activities should follow entrained body
  rhythms
• It is preferable to work during the daylight
  hours
• shift duration of eight hours daily work is
  usually adequate, but
• shorter times for highly demanding jobs may be
  advantageous and
• longer times may be acceptable for some types of
  routine times

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Recommendations II

• either work only one evening or night shift per
  cycle, then return to the day work, and keep
  weekends free
• stay permanently on the same shift
• Compressed worksheets often are acceptable for
  routine jobs - e.g.4 days with 10 hours