Acute Physiological Responses to Exercise

Acute Physiological Responses to Exercise

Key Concepts

• Acute Responses to Exercise: These are immediate changes in the body's systems during and immediately after exercise. These responses are temporary and reversible.
• Body Systems Involved: The primary systems involved are the cardiovascular, respiratory, and muscular systems.
• Dependence on Exercise: Acute responses depend on the intensity, duration, and type of exercise.
• Purpose: These systems work together to supply more fuel and oxygen to working muscles and remove waste products.

Respiratory System

• Ventilation (Increases):

  • Ventilation is the amount of air breathed in and out per minute. It is calculated as: Ventilation (L/min) = Tidal Volume (ml/breath) \times Respiratory Rate (breaths/min)
  • Example: 6 L/min = 500 ml/breath \times 12 breaths/min
  • Tidal Volume: The amount of inspired and expired air per breath increases.
  • Respiratory Rate: The number of breaths per minute increases.
  • Reason: Increased demand for ATP leads to an increased demand for oxygen.

• Ventilation Response Graph:

  • Anticipatory Rise: Ventilation increases slightly before exercise begins.
  • Rapid Rise: Ventilation increases rapidly at the start of exercise.
  • Levelling Off (Steady State): During submaximal exercise, ventilation reaches a plateau where oxygen supply equals demand.
  • Decline: Ventilation decreases during recovery.
  • Rapid Decline: Initial rapid decrease, followed by a slower decrease.

• Diffusion (Increases):

  • Diffusion is the movement of gases from areas of high pressure to areas of low pressure.
  • Lungs:
    • Oxygen moves from the alveoli into the bloodstream due to high oxygen concentration in the alveoli.
    • Carbon dioxide moves from the bloodstream into the alveoli to be exhaled due to high carbon dioxide concentration in the blood.
  • Muscles:
    • Oxygen moves from the bloodstream into the muscles due to low oxygen concentration in the muscles.
    • Carbon dioxide moves from the muscles into the bloodstream to be transported to the lungs and exhaled due to high carbon dioxide concentration in the muscles.

Cardiovascular System

• O2 Consumption (VO2):

  • VO2 is the volume of oxygen consumed.
  • Increases linearly with exercise intensity.
  • VO2 max: The maximal amount of oxygen that can be taken in, transported, and utilized.
  • Formula: VO2 max = Cardiac Output \times aVO2 difference

• aVO2 Difference (Increases):

  • The difference in oxygen concentration in the arterioles compared to the venules.
  • Represents the amount of oxygen used by the muscles.

• Cardiac Output (Increases):

  • Cardiac Output (Q) is the amount of blood pumped out of the left ventricle per minute.
  • Formula: Cardiac Output (Q) = Stroke Volume \times Heart Rate
  • Units: Litres/min = (millilitres/beat) x (beats/min)
  • Resting values: 5 L/min = 70 ml/beat \times 70 beats/min (approx.)
  • Maximal values: 35 L/min = 175 ml/beat \times 200 beats/min (approx.)
  • Stroke Volume: The amount of blood ejected by the left ventricle per beat increases.
  • Heart Rate: The number of beats per minute increases.

• Stroke Volume Plateau: Stroke volume plateaus at submaximal intensity.

• Venous Return (Increases):

  • Mechanisms that increase venous return include:
    • Valve opening and closing in veins to prevent backflow.
    • Contraction of skeletal muscles to squeeze veins and push blood towards the heart.
  • Redistribution of Blood Flow
    *Vasoconstriction of arterioles supplying inactive muscles reduces blood flow
    *Vasodilation of arterioles supplying muscles increases blood flow

• Blood Pressure

  • Normal blood pressure is 120/80 (systolic/diastolic).
    • Systolic: Pressure of blood passing out of the heart.
    • Diastolic: Pressure of blood coming back into the heart.
  • In aerobic activities, systolic blood pressure increases, while diastolic remains relatively stable.
  • In weight resistance activities, both systolic and diastolic blood pressure increase.

• Blood Volume (Decreases):

  • Blood volume decreases due to plasma loss.
  • Blood composition includes plasma (55%), buffy coat (leukocytes & platelets, <1%), and erythrocytes (45%).

Muscular System

• aVO2 Difference (Increases):
  • The difference in oxygen concentration in the arterioles compared to the venules.
  • Represents the amount of oxygen used by the muscles.
• Temperature (Increases):
  • Muscle temperature increases due to heat production during energy metabolism.
• Motor Unit Recruitment (Increases):
  • More motor units are recruited to generate greater force.
• Substrates (Decrease):
  • Energy substrates (such as glucose, glycogen, and fats) are depleted during exercise.
• Lactate (Increases):
  • Lactate accumulation coincides with the accumulation of H+ ions, which contributes to fatigue.

Key Formulas and Equations

• Ventilation: Ventilation = Tidal Volume \times Respiratory Rate
• VO2 max: VO2 max = Cardiac Output \times aVO2 difference
• Cardiac Output: Cardiac Output = Stroke Volume \times Heart Rate