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Energy Expenditure Review

Bioenergetics Review

  • Immediately Available Energy Source: ATP (Adenosine Triphosphate) is the body's immediate energy source.

  • ATP Production from Glycogen: 1 molecule of glycogen through anaerobic glycolysis produces 3 ATP.

  • Rate Limiting Enzyme for Krebs Cycle: Isocitrate dehydrogenase.

  • Effect of High ATP Production on Isocitrate Dehydrogenase: High ATP levels decrease its activity.

  • Net Gain after 2 Turns of Krebs Cycle: 6 NADH, 2 FADH, and 2 ATP.

Energy Expenditure (EE)

  • Definition: Amount of energy used to support the physiological processes of an organism.

  • Rate of Energy Use: Measured via O2 consumption (VO2), which corresponds to caloric expenditure.

  • States of Metabolic Rate:

    • Basal Metabolic Rate (BMR)

    • Resting Metabolic Rate (RMR)

    • Active Energy Expenditure.

Metabolic Rates

  • BMR: Minimum energy required for essential physiological functions, related to fat-free mass (FFM). Reported as kcal/kg FFM/min.

  • RMR: Energy required for resting function; normal range = 1,000-2,500 kcal/day.

  • Determinants of BMR/RMR:

    • Higher FFM leads to greater body surface area.

    • Biological sex: Males generally have a higher BMR.

    • Body temperature and age: Higher temperatures and younger age increase BMR.

    • Energy intake: Lower intake reduces BMR.

    • Caffeine, tobacco, and stress increase BMR.

Daily EE Components

  • Components of Daily EE:

    • Resting Metabolic Rate (RMR)

    • Thermic Effect of Food (TEF) - energy used for digestion and assimilation.

    • Thermic Effect of Activity (TEA) includes both planned physical exercise and non-exercise activity thermogenesis (NEAT).

  • Energy Expenditure Norms:

    • Regular activity: 1,800 - 3,000 kcal/day.

    • Competitive athletes: ≥ 10,000 kcal/day.

Importance of EE

  • Variability in resting metabolic rate (RMR) influences weight gain risk.

  • Low fat to carbohydrate oxidation ratios are predictors of weight gain, established through studies measuring respiratory quotients.

Measuring EE

Direct Calorimetry

  • Heat production increases with body temperature. Water temperature rises as body heat increases.

  • Pros: Highly accurate over time; ideal for measuring RMR.

  • Cons: Expensive and impractical for high-intensity exercises; measurements can be affected by heat and sweat.

Indirect Calorimetry

  • Calculates EE from gas exchange: O2 consumption and CO2 production; RER = VCO2 / VO2 with a range of 0.7 - 1.0.

  • RER and Substrate Utilization:

    • CHO oxidation RER = 1.0: equation C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + 32 ATP.

    • Fat oxidation: 23 O2 with RER calculated as needs.

Exercise Intensity and EE

  • As exercise intensity increases, so does EE.

  • RER shifts from ~0.8 at rest to ~1.0 during intense exercise, indicating a shift from fat to carbohydrate utilization.

VO2 and Maximal Capacity

  • VO2max: Maximal oxygen uptake during intense exercise; important for aerobic fitness assessment. Norms:

    • Untrained men: ~35-45 mL/kg/min.

    • Untrained women: ~25-35 mL/kg/min.

Anaerobic Contributions to EE

  • O2 Deficit: Occurs at the onset of exercise when oxygen demand surpasses consumption.

  • EPOC (Excess Post-exercise Oxygen Consumption): Elevated VO2 after exercise, helps to restore ATP/PCr stores and remove lactate.

Individual Performance Indicators

  • Lactate Threshold: The point when blood lactate rises significantly; indicates performance capacity for sustained exercise.

  • Higher lactate threshold percentages correspond to better endurance performance; trained individuals show increased thresholds compared to untrained individuals.

EE for Activities

  • Energy expenditures vary greatly among physical activities, as shown in various tables during exercises such as cycling, running, and swimming.

  • Factors like age, gender, body mass and physical activity type influence EE calculations.

Summary of Key Points

  • Daily EE = RMR + TEF + TEA; measured directly or indirectly.

  • VO2 increases with exercise intensity, and training can enhance VO2max.

  • Understanding anaerobic contributions, O2 deficit, and EPOC helps in maximizing performance.

Study Questions

  • Describe energy expenditure (EE), metabolic rate, their determinants.

  • Discuss direct vs indirect calorimetry along with advantages and disadvantages.

  • Explain how exercise intensity, substrate utilization, and lactate threshold influence energy expenditure and athletic performance performance.

To calculate the final number of ATP produced from a 12-carbon fatty acid, we consider beta-oxidation and the Krebs cycle:

  1. Beta-oxidation cycles: A 12-carbon fatty acid undergoes (12/2) - 1 = 5 cycles of beta-oxidation.

  2. Acetyl-CoA production: Each cycle removes 2 carbons as acetyl-CoA, so 12/2 = 6 molecules of acetyl-CoA are produced.

  3. ATP from beta-oxidation: Each cycle produces 1 NADH and 1 FADH2.

    • 5 NADH will yield 5 \times 2.5 = 12.5 ATP.

    • 5 FADH2 will yield 5 \times 1.5 = 7.5 ATP.

    • Total from beta-oxidation: 12.5 + 7.5 = 20 ATP.

  4. ATP from Acetyl-CoA in Krebs cycle: Each acetyl-CoA entering the Krebs cycle produces 10 ATP (3 NADH at 2.5 ATP each = 7.5 ATP; 1 FADH2 at 1.5 ATP = 1.5 ATP; 1 GTP/ATP = 1 ATP).

    • 6 Acetyl-CoA molecules will yield 6 \times 10 = 60 ATP.

  5. ATP investment: The initial activation of the fatty acid requires 2 ATP equivalents.

Total Net ATP: 20 (from beta-oxidation) + 60 (from Krebs cycle) - 2 (initial investment) = 78 ATP.

Therefore, breaking down a 12-carbon fatty acid will produce approximately 78 ATP.

Vo2 max is not the best predictor of endurance performance, as it does not account for other factors such as lactate threshold and efficiency of energy utilization during prolonged exercise.

lactate threshold-

lactate threshold (LT)-point at which blood lactate substantially rises above resting levels

lactate production is greater than the clearance

good indicator of performance potential of endurance exercise