Psyc 552 Ergonomics

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Psyc 552 Ergonomics Biomechanics

• Lecture 13

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Work Physiology

• Started in 1913 by Max Rubner in Berlin.
• Discipline grew in an effort to understand where
  humans could operate.
• War was the primary motivator. The cold war
  prompted much study.

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Work Exercise Physiology

• At one time both were studied togetherdifferences
  in physiological demand caused the two to
  disciplines to separate.
• Workers rarely exceed 30 to 40 of their maximum
  aerobic capacity. Athletes regularly exceed
  these rates.
• Today, more exercise physiology research.

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Work physiology basics

• Simple, infrequent lifting produces mechanical
  forces -- Carrying, repetitive lifting,
  walking create physiological demands.
• Carrying, repetitive lifting, and walking can
  exceed the anaerobic energy stores.

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Aerobic Process

• Continuous muscle contractions are supported by
  the aerobic process where carbohydrates and/or
  fat are oxidized in the presence of oxygen.
• For each liter of O2, about 5 kcal of energy are
  generated.

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kilocalories

• Calorie unit of energy the amount of energy
  or heat needed to raise the temperature of 1 gram
  of water by 1 degree Celsius.
• 1 gallon of gasoline 31,000,000 calories or
  31,000 Calories
• Food is measured in kcals or Calories not
  calories.

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Work limits

• NIOSH limits aerobic work to 9.5 kcal/min
• A limit of 70 of maximum aerobic capacity for
  arm work.
• Limits of 50, 40, and 33 of maximum aerobic
  capacity for 1 hour, 1 to 2 hour, and 2 to 8 hour
  work.

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Work Levels
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Maximum Aerobic Capacity

• Can be assessed by
• Running on a treadmill
• Exercising on a cycle ergometer
• Step test
• Expired air is collected and measured for volume
  and O2 content.

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Maximal tests at work

• Maximal tests and are not common in work
  environments.
• Shortcomings

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Submaximal tests

• We can estimate maximum aerobic capacity based on
  the relationship between heart rate and oxygen
  consumption.

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Assumptions

• Linearity of heart rate oxygen consumption
  relationship.
• Similar maximum heart rates for all subjects
• Constancy of mechanical efficiency.

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Factors Affecting Aerobic Output

• Training adaptation
• Sex Age

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Factors (cont)

• Anthropometry
• Nutrition

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Factors (cont)

• Psychological factors
• Type of work

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Factors (cont)

• Work duration
• Technique

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Factors (cont)

• Environment