Hard and Light Physical Work

1
Hard and Light Physical Work

• IENG 321
• Ergonomics and Human Factors Engineering
• Spring 2009

2
Physiological Principles

• Increasing metabolic demands of skeletal muscle
  during hard work
• Nutrient and O2 supply
• Removal of metabolic waste
• Body temp control
• Design physical tasks for many

3
Energy Units

• Work
• Joules and calories
• 4.19J 1 cal
• 1 J 1Nm .7386 ftlb .2389 cal .948 x 10-3
  BTU
• Power
• Watts
• 1 W 1 J/s
• 1 kcal/hr 1.163 W

• Food energy values (cal/g)
• Alcohol 7
• Carbohydrate 4.2
• Protein 4.5
• Fat 9.5

4
Metabolism

• Converting fuel (food, drink, stored energy) into
  mechanical energy
• Absorbed by blood and lymph
• Controlled mainly by the liver
• Glucose and glycogen first energy source
• Fat largest source but last to be used

5
Metabolism

• Basal
• Minimum energy requirements of body with no
  activity
• 1 kcal per kg body mass per hour
• Resting
• Rested as much as possible
• 10 15 greater than Basal
• Work
• Increase between resting and working
• Measure using
• VO2
• Heart rate

6
VO2

• O2 consumption measure of metabolic activity
• Difference in O2 between exhaled and inhaled air
• Average energy value 5 kcal/L O2
• Respiratory Quotient
• More detailed assessment of nutrients metabolized
• Volume CO2 expired to O2 consumed
• Carbohydrate (1), Protein (.8), Fat (.7)

7
Heart Rate

• Greater heart rate for increased metabolic
  demands
• Linear relationship between heart rate and VO2
• Use heart rate to assess metabolic demands
• Dependant on age, gender, physical fitness

8
Heart Rate

• Steady State Work
• Effort stays at or below max capacity
• Blood flow, O2, respiration can maintain required
  levels
• Fitness an important factor

9
Limits of Capacity

• Exceeding abilities not allowing for steady state
• Recovery (even to resting levels)
• Physical fitness and skill important

10
Limits of Capacity
11
Static Work

• Exceeding 15 muscular strength limits blood
  flow
• Increased heart rate, decreased metabolism

12
Designing Heavy Work

• Humans inefficient machines (5 or less of energy
  converted to work)
• Dont exclude
• Design for energy output, neuromuscular function,
  and psychological factors for many
• Avoid exhausting work.
• 2900 3600 kcal (males)
• 2400 2900 kcal (females)
• Provide rest breaks
• Minimize/eliminate static work

13
Designing Heavy Work
14
Light and Moderate Work

• Lighter metabolic demands, considerations for
  diligence with
• Attention to detail
• Endurance (Repetition)
• Physical environment
• Climate
• Sound levels
• Lighting
• Psychosocial

15
Tiredness, Boredom, Alertness

• Diversity vs. Monotony
• Taylorism

• Vigilance vs. Frequency

16
Work Postures

• Minimize/eliminate static work
• Avoid non-neutral postures
• Sitting (less fatiguing)
• Space for legs
• Get up and move occasionally

17
Accurate, Fast, Skillful Movement

• Exact manipulations
• Waist height in front of the trunk
• Possibly higher depending on level of required
  control

18
Vision

• 30 degree cone around line of sight
• Based on LOSEE

19

• Questions?