58. Physiology of work. Changes in the body during work

What does work physiology study?

It examines how the human body responds to physical and mental demands of work. This includes:

• Physiological changes (heart rate, oxygen use)

• Psychological stress

• Working capacity (endurance, strength)

• Fatigue development and recovery

• Impact of shift work on circadian rhythm

• Ergonomics and workplace adaptation

• Effects of environmental conditions (heat, noise, light) on health and performance.

What is ergonomics?

• Ergonomics is the science of designing tasks, tools, and environments to suit human anatomy and cognitive abilities.
  

• Its goal is to reduce fatigue, discomfort, and risk of injury while improving productivity and safety.

What are the goals of modern ergonomics?

• Optimize workplace layout and equipment (e.g., desks, chairs)

• Design movement and task sequences to reduce awkward or repetitive motions

• Minimize physical and mental strain

• Promote healthy work-rest cycles to prevent overexertion

• Enhance worker comfort and productivity.

What are the two types of muscle work?

1. Static work: Muscle tension without movement (e.g., holding a heavy object).

2. Dynamic work: Muscle contraction with movement (e.g., walking, lifting).

• Static work can impair circulation and cause fatigue faster.

What happens to oxygen consumption during dynamic physical work?

• Oxygen consumption increases significantly to supply energy for muscle activity.

• The body shifts to aerobic metabolism, using oxygen to produce ATP.

• In intense work, anaerobic metabolism may kick in, producing lactic acid.

How does the respiratory system respond during physical work?

• Tidal volume (amount of air per breath) increases.

• Respiratory rate rises to enhance oxygen intake and CO₂ removal.

• Overall, minute ventilation increases to meet metabolic demands.

How does the cardiovascular system respond to physical work?

• Heart rate and stroke volume increase to pump more blood.

• Cardiac output (HR × SV) rises significantly.

• Systolic blood pressure increases due to higher cardiac output.

• Blood flow is redistributed to working muscles.

What blood changes occur during physical work?

• Temporary hemoconcentration (higher RBC and hemoglobin levels due to fluid loss).

• Increase in lactic acid from anaerobic metabolism.

• Enhanced oxygen extraction from hemoglobin by muscles.

What is the energy unit for biological activity?

• ATP (adenosine triphosphate) is the primary energy currency.

• It fuels all muscle contractions and cellular processes.

• ATP is regenerated from carbohydrates, fats, and proteins.

What body systems adjust to meet oxygen demand during work?

• Cardiovascular system: increases heart rate and stroke volume.

• Respiratory system: boosts ventilation.

• Circulatory system: increases arteriovenous oxygen difference.

• Nervous system: coordinates responses via sympathetic activation.

How is energy for physical activity obtained?

• Food is digested into nutrients, mainly glucose and fatty acids.

• These are absorbed and transported to cells.

• In the presence of oxygen, they are metabolized in mitochondria to produce ATP.

• The body prioritizes carbohydrates during intense work and fats during prolonged moderate work.