Exercise Physiology Exam 2

Increasing prevalence of overweight/obesity since ~1980 suggests that many people live in a chronic energy surplus o Energy surplus means the energy expenditure is less than energy intake ▪ Strongly associated with significant reductions in physical activity energy expenditure

• Three primary processes of energy expenditure o REE (60-75% in average adult) o PAEE (15-30% in average adult) ▪ Remember, three key ATPases and what they do! o TEF (~10% in average adult) ▪ Effects of macronutrient makeup of diet on TEF and TDEE? - TEF for protein? ~20-30% - TEF for CHO? ~5-10% - TEF for fat? ~0-3% ▪ What does the consumption of a mixed meal (i.e., a meal comprised of each of the macronutrients) do to VO2 during the digestive process? Increases VO2 due to energy needed for digestion and absorption ▪ What does the consumption of a mixed meal do to RER during the digestive process? Increases RER due to a higher proportion of CHO oxidation

o Of the three processes of energy expenditure, PAEE is the most easily, immediately, and significantly changeable ▪ EE in muscle fiber can increase 100x above rest when contracting

• What is a MET? o VO2? 3.5 mL/kg/min o Energy expenditure? 1 kcal/kg/hr

• What is our metabolic efficiency? o ~60% of our energy expenditure is immediately “lost” in the form of heat

• What is “direct calorimetry?” o Advantages of this technique? Accurately measures total heat production o Key issues for use during exercise? Expensive, impractical, and limited application in dynamic settings

• What is “indirect calorimetry?” o What is a metabolic analyzer (often called a metabolic cart, or “met cart”)? Device measuring O2 consumption and CO2 production o What must be measured to be able to determine energy expenditure via indirect calorimetry? ▪ Oxygen consumption ▪ Carbon dioxide production o The basis of this process is that amount of inspired oxygen is equal to the amount of expired nitrogen over any period of time ▪ 79% of our air is comprised of nitrogen ▪ 21% of our air is comprised of oxygen ▪ ~0.03-0.04% of our air is comprised of carbon dioxide

• Indirect calorimetry allows us to calculate the respiratory exchange ratio (RER) o Formula? VCO2/VO2 o Two important pieces of information that we can learn from RER are substrate utilization and energy expenditure o The range of RER (during steady-state conditions) is from a low of 0.7 to a high of 1.0 ▪ What does a low RER indicate? Predominant fat oxidation - Compared with CHO, FA requires more oxygen to fully oxidize - Energy provided per liter of oxygen consumed? ~4.7 kcal ▪ What does a high RER indicate? Predominant CHO oxidation - Energy provided per liter of oxygen consumed? ~5.05 kcal

• Why is it optimal that RER increases as the intensity of exercise increases? o Carbohydrates provide a more rapid source of ATP, needed when oxygen availability is limited

• Where does the carbon dioxide that we exhale come from? o Oxidation of glucose and fatty acids in metabolic processes

• At rest, most healthy young people exhibit an RER of ~0.8 o At resting RER, ~60% of whole-body energy is being provided by the oxidation of fatty acids

• Under what conditions can RER (measured at the mouth) exceed 1.0? o During high-intensity exercise due to buffering of lactate and increased CO2 production

• Energy expenditure using “doubly-labeled water” o What is an isotope? Variant of an element with a different number of neutrons o What is doubly labeled water? Water with isotopes of hydrogen and oxygen o Considered a gold-standard method of determining energy expenditure in free-living conditions

• Estimation of energy expenditure via heart rate? o Basis of this method is that there is a very strong correlation between VO2 and heart rate

• Energy expenditure using accelerometers and pedometers o Key differences? Accelerometers measure movement intensity; pedometers only count steps o Effect of placement on results? Accuracy varies depending on location (e.g., wrist vs. hip)

• Energy expenditure by self-report o Bias? Overestimation common; CDC reports ~50% of adults meet PA guidelines, but accelerometer data suggests only ~10%

• Expressing VO2 o Most common expression is mL/kg/min o What expression is necessary to allow for determination of energy expenditure? L/min

• Prediction of VO2 during walking o VO2 = 0.1 x speed + 1.8 x speed x grade + 3.5

• Prediction of VO2 during running o VO2 = 0.2 x speed + 0.9 x speed x grade + 3.5

• Prediction of VO2 during cycle ergometry o VO2 = ((workload x 1.8)/body weight in kg) + 3.5 + 3.5

• VO2 max o Most common expression is mL/kg/min o Average college-aged male = ~45-50 mL/kg/min o Average college-aged female = ~35-40 mL/kg/min

• LT (Lactate Threshold) o The exercise intensity at which lactate production exceeds lactate clearance

• Optimal endurance performance requires: o High VO2 max (greater capacity for aerobic ATP production) o High LT (ability to sustain high intensities aerobically) o Excellent economy (lower VO2 for a given workload) o Type I muscle fibers (fatigue resistance)

• Greatest modifiable influence on energy expenditure? Physical activity

  • Energy expenditure vs. energy intake: Energy expenditure is less than energy intake.

  • REE: (~ 60-75% in the average adult).

  • PAEE: (~ 15-30% in the average adult).

  • TEF: (~ 10% in the average adult).

  • Effects of macronutrient makeup on TEF and TDEE:

    • Protein: 20-30%

    • Carbohydrates (CHO): 5-10%

    • Fat: 0-3%

  • Mixed meal and VO2/RER:

    • Consumption of a mixed meal increases VO2 due to the thermic effect of digestion.

    • Mixed meal increases RER, reflecting a shift to more carbohydrate oxidation during digestion.

  • Most changeable energy expenditure process: PAEE (Physical Activity Energy Expenditure).

  • EE in muscle fiber: Can increase several times above rest when contracting.

  • MET (Metabolic Equivalent of Task):

    • VO2: Volume of oxygen consumed.

    • Energy expenditure: Energy used by the body during physical activity.

  • Metabolic efficiency: Around 60-70% of our energy expenditure is immediately “lost” as heat.

  • Direct calorimetry: Measures heat production directly.

    • Advantages: Accurate measurement of total heat production.

    • Key issues: Difficulty during exercise due to heat loss and environmental variables.

  • Indirect calorimetry: Measures VO2 and VCO2 for estimating energy expenditure.

    • Measures oxygen consumption and carbon dioxide production.

    • Inspired oxygen equals expired carbon dioxide.

    • Nitrogen: 78%, Oxygen: 21%, CO2: 0.04%.

  • RER Formula: RER = VCO2 / VO2.

    • Provides insight into substrate oxidation and respiratory efficiency.

  • Low RER indicates: Primarily fat oxidation.

    • High RER indicates: Primarily carbohydrate oxidation.

  • RER and exercise intensity: RER increases during higher intensity due to increased reliance on carbohydrates.

  • Carbon dioxide in exhalation: Produced from the oxidation of glucose and fatty acids.

  • RER at rest: ~ 0.78-0.82.

    • Fat oxidation contributes around 60-70% of energy.

  • Doubly-labeled water: Gold standard for estimating energy expenditure in free-living conditions.

  • Heart rate method: Correlates heart rate with energy expenditure.

  • Self-report bias: Overreporting or misreporting activity levels.

    • CDC reports: ~ 50% of adults report meeting physical activity guidelines, but actual data shows only 20-30%.

  • VO2 Expression: Most common expression is relative VO2 (ml/kg/min).

  • Prediction of VO2 during walking/running/cycle ergometry:

    • Walking: VO2 = 0.1 x speed + 1.8 x speed x grade + 3.5.

    • Running: VO2 = 0.2 x speed + 0.9 x speed x grade + 3.5.

    • Cycle ergometry: VO2 = (workload x 1.8) / body weight + 3.5.

  • VO2 max plateau: Occurs after around 8-12 weeks of training.

  • VO2 max in athletes: Higher in endurance athletes due to training adaptations.

  • Oxygen deficit: Occurs when VO2 increases gradually at the start of exercise.

  • EPOC (Excess Post-Exercise Oxygen Consumption):

    • Fast component: Clearance of lactate and replenishment of phosphocreatine.

    • Slow component: Increased temperature and metabolic rate.

  • LT (Lactate Threshold): The point where lactate production exceeds lactate clearance.

    • Excellent predictor of endurance performance.

    • Can be increased without improving VO2 max.

  • Economy of movement: Refers to the oxygen cost at a given workload; optimal in activities practiced most frequently.