Metabolic Rate and Heat Production

Key Concepts

• Metabolism and Heat: Metabolism is tied to heat production because chemical reactions are inefficient—about 60% of energy is lost as heat.
• Mechanical Work: Activities like rubbing hands generate heat through muscle proteins actin and myosin.

Measuring Metabolic Rate

• Calorimeter: Direct measurement through heat liberation, typically more effective in water.
• Respirometer: Indirect measurement through oxygen consumption, linked to metabolic rate as oxygen is the final electron acceptor in the electron transport chain.

Basal Metabolic Rate (BMR)

• Definition: Energy needed for essential body activities in a post-absorptive, relaxed state at room temperature.
• Measurement: Recorded in kcal per square meter of body surface per hour.

Influencing Factors

• Surface Area to Volume Ratio: High ratio in thin individuals leads to higher metabolic rates to maintain body temperature.
• Age: BMR decreases with age due to reduced physical activity.
• Gender: Males generally have higher BMR due to more muscle mass and testosterone's anabolic effects.
• Temperature & Stress: Increase BMR to generate more heat or energy.
• Thyroxine: Hormone increases oxygen consumption, heart rate, and cellular respiration, thus elevating BMR.

Total Metabolic Rate

• Definition: Kcal consumption rate for all activities, beyond just essential processes.
• Influencing Factors:
  • Physical Activity: Increases total metabolic rate, though not necessarily BMR.
  • Food Ingestion: Food-induced thermogenesis raises metabolic rate, especially with high protein and alcohol intake.