Unit 3 AOS 2: Energy Production in the Body

Oxygen Uptake at Rest, Oxygen Deficit, Steady State, and Recovery

Oxygen Uptake

• Oxygen uptake is examined at rest, during physical activity, and during recovery, including oxygen deficit, steady state, and excess post-exercise oxygen consumption (EPOC).

Oxygen Uptake at Rest

• At rest, the body requires minimal oxygen (O2) consumption because the body's need for ATP is reduced.
• As the body becomes active, O2 consumption increases, which allows working muscles to be supplied with increased levels of ATP.

Oxygen Deficit

• Definition: The difference between the amount of oxygen consumed and the amount of oxygen that would have been consumed if a steady state had been reached from the start of exercise.
• During the transition from rest to exercise, and particularly during high-intensity exercise or when exercise intensity increases, there is a discrepancy between the amount of O2 required and the amount supplied and used. This discrepancy is the oxygen deficit.
• Under these conditions, anaerobic pathways (ATP-CP and Anaerobic Glycolysis system) must supplement the energy demands of the activity.
• The oxygen deficit occurs because the respiratory and cardiovascular systems take time to adjust to the new oxygen demand, even at low exercise intensities.
• Adjustments include:
  • Increased Respiratory Rate (RR)
  • Increased Tidal Volume (TV)
  • Increased Heart Rate (HR)
  • Increased Stroke Volume (SV)
• The size of the oxygen deficit is dependent upon the exercise intensity; the greater the intensity, the greater the debt!
• The debt serves to replenish energy stores utilized during exercise.
• Large oxygen deficit early in event is covered by the ATP- PC and Anaerobic Glycolysis systems ability to supply ATP anaerobically. The athlete can work above 100% of their VO_2 max due to the contribution of the anaerobic energy systems.

Limitations of Anaerobic Energy Systems

• Due to the limitations of the two anaerobic energy systems, specifically depletion of PC and accumulation of lactic acid, H^+ ions, and other metabolic by-products, it is very difficult to sustain high-intensity exercise for longer than 30 seconds.
• The aerobic energy system 'lags' in its ability to contribute large amounts of energy in the first 20 to 30 seconds of exercise because of the more complex chemical reactions required to resynthesise ATP.

Steady State

• Definition: The state in which oxygen supply equals oxygen demand, so almost all of the required ATP to maintain the current exercise intensity is being supplied aerobically.
• Once oxygen supply equals oxygen demand, the body reaches a steady state.
• This steady state in oxygen uptake coincides with a plateau in heart rate and ventilation.
• If exercise intensity increases again, the demand for ATP resynthesis and O_2 also increases.
• If the aerobic system cannot meet these demands, the anaerobic pathways must supplement the energy supply until a steady state is reached once more.
• Reaching a new steady state is only possible when lactate removal is greater than lactate production.

Excess Post-Exercise Oxygen Consumption (EPOC)

• Also referred to as the 'Oxygen Debt'.
• Definition: When oxygen supply is greater than oxygen demand post-exercise.
• Exhausting, high-intensity exercise results in larger EPOC than exercise at lower workloads/intensities.
• After exercise, the demand for ATP decreases dramatically; however, oxygen consumption is still higher than at resting levels.
• Typically occurs during a warm-down.
• O_2 consumption is extended when an active recovery is undertaken, which assists in the removal of metabolic by-products.
• EPOC can be divided into two parts:
  • Fast Replenishment:
    • Restores PC.
    • Takes approximately 2-3 minutes.
  • Slow Replenishment:
    • Removal of lactic acid and H^+.
    • The greater the accumulation of lactic acid, the larger EPOC will be.
    • It can take hours to complete, depending on the size of the debt.
    • Return core temperature to pre-exercise levels.
    • Remove lactic acid through the conversion of lactate → glycogen in the liver.
    • Supply active tissues such as the heart and respiratory system.
    • Replace depleted oxygen stores in the body.

Relationship between Exercise Intensity, Oxygen Deficit, Steady State, and EPOC