1. ACUTE RESPONSES TO PHYSICAL ACTIVITY YEAR 11 PE-Year 12 Content

2. ACUTE RESPONSES TO PHYSICAL ACTIVITY ACUTE RESPONSES- Immediate, short-term responses to exercise that last only for the duration of the training or exercise session and recovery period. These changes occur in the cardiovascular, respiratory and muscular systems.

3. ACUTE RESPONSES OF THE MUSCULAR SYSTEM TO PHYSICAL ACTIVITY INCREASED MOTOR UNIT AND MUSCLE FIBRE RECRUITMENT AND MUSCLE CONTRACTIONS When exercise begins, motor unit recruitment must increase so that more muscle fibres can be activated to contract. The greater the force required, the greater the number of motor units recruited and the greater the number of muscle fibres activated for contraction. INCREASED BLOOD FLOW TO THE MUSCLES Due to increase demand for oxygen during exercise, this leads to: Vasodilation of capillaries Redistribution of blood from organs to skeletal muscles.

4. ACUTE RESPONSES OF THE MUSCULAR SYSTEM TO PHYSICAL ACTIVITY INCREASED MUSCLE TEMPERATURE Increase in muscle temperature during exercise is due to: Increased blood flow to working muscles Heat generated as a by-product of ATP production DEPLETION OF MUSCLE ENERGY STORES Muscular sources of fuel for energy production (ATP, PC, glycogen and triglycerides) begin to deplete during exercise.

5. ACUTE RESPONSES OF THE CARDIOVASCULAR SYSTEM TO PHYSICAL ACTIVITY INCREASED HEART RATE Heart rate increases with increasing exercise intensity to assist with greater demand for oxygen for muscle contraction and removal of wastes. INCREASED STROKE VOLUME Stroke volume increases due to increased demand for oxygen for muscle contraction during exercise, allowing more blood to be pumped from the heart with each beat. INCREASED CARDIAC OUTPUT Cardiac output increases during exercise due to increase in heart rate and stroke volume.

6. ACUTE RESPONSES OF THE CARDIOVASCULAR SYSTEM TO PHYSICAL ACTIVITY INCREASED SYSTOLIC BLOOD PRESSURE During exercise, blood is being pumped more forcefully into arteries, due to increase demand for oxygen supply to active muscles. INCREASED BLOOD FLOW AND BLOOD VESSEL DIAMETER Speed and volumed of blood flow to active muscles increasing with exercise, causing blood vessels to increase in diameter (vasodilation). BLOOD FLOW REDISTRUBUTION Blood is redistributed to active muscles from other areas of the body where not required during exercise, to increase supply of oxygen to working muscles. Blood flow can also be redistributed to skin for the removal of heat (produced as a by-product to energy production).

7. ACUTE RESPONSES OF THE CARDIOVASCULAR SYSTEM TO PHYSICAL ACTIVITY INCREASED BODY TEMPERATURE Increase in body temperature occurs due to an increase in metabolism by active muscles. As muscles work harder to contract, more heat is produced as a by-product of exercise. INCREASED ARTERIOVENOUS DIFFERENCE (a-VO² diff) Comparison of amount of oxygen in veins compared to that in the arteries. With increasing exercise intensity, the amount of oxygen in veins (blood returning from body) is lower than at rest, causing a greater difference in oxygen concentration in arteries and veins. No change in oxygen concentration of arteries during exercise.

8. ACUTE RESPONSES OF THE RESPIRATORY SYSTEM TO PHYSICAL ACTIVITY INCREASED RRSPIRATORY (BREATHING) RATE Respiratory rate increases during exercise due to an increase demand for oxygen and removal of carbon dioxide. INCREASED TIDAL VOLUME Tidal volume increases with increasing exercise intensity to supply oxygen to working muscles. INCREASED VENTILATION Due to increases in respiratory rate and tidal volume during exercise, ventilation also increases.