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