Temporal Ergonomics

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Chapter 21

• Temporal Ergonomics

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Reducing Fatigue

• Maintains or increases work productivity
• Provides optimal stress
• Consider and optimize both goals.

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Kinds and Locations of Fatigue

• General body fatigue
• Muscular fatigue
• Mental fatigue

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Factors in Fatigue

• Physical exertion
• Physical discomfort
• Lack of energy
• Lack of motivation
• Sleepiness

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Factors in Recovery Value of Rest

• How fatigued the muscle is when the rest begins
• The length of the rest
• What happens to the muscle during rest

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Axioms

• Most jobs have peaks and valleys of demand.
• Fatigue increases exponentially with time.
• Rest is more beneficial when it occurs prior to
  too much fatigue.
• The value of rest decreases exponentially with
  time.
• Different parts of the body have different
  recovery rates.
• Active rest and working rest are alternatives to
  passive rest.
• There is output during work and no output
  during rest.

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Work Hours

• Most countries have a workweek of 40 hours or
  less.
• The number of hours worked per year also has
  declined.
• The hours worked per lifetime has declined.
• Daily hours have changed.
• Firms use overtime instead of inventories.
• Firms use part-time workers.
• A compressed workweek is becoming more common.

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Rest Hours (Allowances)

• Normal time is developed from time studies.
• Normal time is adjusted with allowances to yield
  standard time.
• Allowances are based on an 8-h day and 5-day
  week.
• Allowances consider only duration of rest.
• Each minute of rest is assumed to be equally
  valuable.

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Cardiovascular System

• Fatigue occurs during heavy work (e.g. manual
  handling).
• Percent of capacity depends on work duration.
• NIOSH Lifting Guidelines consider
  short/moderate/long categories of lifting
  duration.

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Musculoskeletal System

• Static work
• Dynamic work
• VDT work

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Muscle Fatigue

• Types of muscles
• Slow-twitch
• Fast-twitch
• Static work is more fatiguing than dynamic work.

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Muscle Recovery Time
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Effect of Load
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VDT Work

• Time before a break
• Break length
• Microbreaks
• Active/working/passive rest

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Brain

• Optimum stimulation decreases fatigue.
• Lack of motivation increases fatigue.
• Overload and underload predict fatigue.

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Concentrationand Attention

• Are vulnerable to overload and underload.
• Regulatory agencies provide guidelines for work
  hours and rest.
• Changes that reduce boredom are beneficial.

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Sleep

• Restores the functions of the brain.
• Sleep duration follows a normal distribution.
• Many people have mild, chronic sleep deprivation.
• Sleep deprivation of 2448 h affects motivation.
• Longer sleep deprivation affects ability to
  perform.

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Circadian Rhythm

• Various physiological functions vary in a daily
  pattern.
• The period is about 25 h without external clues.
• The main zietgeber is outdoor light and darkness.
• Alertness peaks in the later afternoon and
  bottoms during the night.
• Morning people tend to be less tolerant to
  shiftwork.

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Countermeasures to Sleep Deprivation

• Rest
• Naps usually take place in the afternoon.
• Investment naps may aid alertness.
• Nighttime naps are of some benefit.
• Sleep inertia may result from night naps.
• Drugs/Food
• Caffeine and amphetamines are effective.
• Short-acting sedatives may aid daytime sleep.
• Alcohol and older antihistamines increase
  sleepiness.
• Effects of some compounds are affected by
  circadian rhythm.
• Food with carbohydrates may relieve fatigue.

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Countermeasures to Sleep Deprivation (cont.)

• Environmental Stimulation
• Bright lights
• Ventilation
• Auditory stimulation
• Conversation
• Physical activity

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Shiftwork

• Shiftwork means not starting work between 7 am
  and 9 am
• 2030 of workers are on some kind of shiftwork.
• Expensive capital encourages shiftwork.
• Social need may require shiftwork.

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Shiftwork Problems

• Economic higher pay
• Social
• Scheduling social activities
• Child care
• Health/safety

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Shift System Design Recommendations

• Avoid permanent night work for the majority of
  shiftworkers.
• Consider advantages and disadvantages of 12-h
  shifts.
• Avoid an early start for the morning shift.
• Consider distribution of leisure time.
• Rotate forward.
• Make the schedule simple and predictable.

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Shiftwork Planning

• Decide on total hours/day of operation.
• Decide on 5-day or 7-day plan.
• Consider having workers in different time zones.
• Decide on fixed, alternating, or rotating shifts.

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Guideline 1

• Have a Work Scheduling Policy
• Problem is insufficient rest.
• Avoid too many hours.
• Avoid work hours at the wrong time.

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Guideline 2

• Optimize Stimulation During Work
• Problem is too much or too little stimulation.
• For too much stimulation, reduce environmental
  stimulation.
• For too little stimulation
• Add physical activity.
• Add task variety.
• Add environmental stimulation.

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Guideline 3

• Minimize the Fatigue Dose
• Problem is that fatigue may become too great.
• Reduce high stress levels.
• Permit rest before fatigue becomes excessive.
• Schedule a break.
• Use part-time workers.

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Guideline 4

• Use Work Breaks
• Problem is that there is no productivity during
  break.
• Work with a different part of the body to rest
  the fatigued part.
• Rest during the automatic part of a machine
  cycle.
• Consider job rotation.

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Guideline 5

• Give Frequent Short Breaks
• Problem is how to divide break time.
• Remember that fatigue recovery is exponential.
• Give breaks in small segments, during the work
  period.
• Permit operator-controlled breaks if possible.

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Guideline 6

• Maximize the Recovery Rate
• Problem is to recover as quickly as possible.
• Reduce contact with environmental stressors.
• Provide good blood circulation for muscle
  recovery.
• Take active rest.
• Consider working rest.

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Guideline 7

• Increase the Recovery/Work Ratio
• The problem is insufficient time to recover.
• Increase the recovery time or decrease the work
  time.
• Moonlighting and 12-h shifts can cause problems.
• Encourage rest on holidays, weekends, and
  vacations.