Acute Responses to Exercise Chapter 4 Acute Responses to Exercise

Robert Malpeli - Balwyn High School 2010

Acute Responses Immediate physiological responses to exercise are called acute responses. The body responds to the demands of exercise by making a number of physiological short-term changes to the cardiovascular, respiratory and muscular systems. Once the exercise is stopped, these three systems will return to pre-exercise levels.

Robert Malpeli - Balwyn High School 2010 Acute responses : Only occur for the duration of exercise and recovery Are dependent on the intensity, duration and type of exercise being undertaken Involve the respiratory, cardiovascular and muscular systems working together to supply more energy / ATP and oxygen to working muscles and then again to remove any waste products Robert Malpeli - Balwyn High School 2010

Any of the acute respiratory responses aim to increase the oxygen supply / concentration of the blood to enable more oxygen to be available to the working muscles for aerobic metabolism.

Ventilation Exercise places increased demands on the body’s need for oxygen to meet the rising energy demands of the activity. Ventilation increases prior to the beginning of exercise and continues to rise to meet the oxygen demands of the exercise. Increases in ventilation are a result of an increase in tidal volume, respiratory rate, or both.

At submaximal exercise intensities, ventilation will increase linearly with oxygen consumption (VO2) until a steady state (plateau) is reached. At maximal intensities, ventilation increases until the exercise is stopped. After the ventilator threshold is reached, ventilation continues to increase non-linearly.

When exercise begins, muscular contractions increase to enable exercise to occur. The body’s responses to exercise are primarily responsible for increasing the amount of oxygen delivered to and used by the working muscles.

Robert Malpeli - Balwyn High School 2010 ↑ Gas Exchange / Diffusion Gases such as oxygen and carbon dioxide always move from areas of high pressure to areas of low pressure. Lungs oxygen concentration is high so it moves from the alveoli into the blood stream to be taken to muscles carbon dioxide concentration in the blood stream is high so it moves into the alveoli to be exhaled Muscles (opposite concentrations to lungs) oxygen concentration is low so it moves from the blood stream to be taken in by the muscles carbon dioxide concentration in the muscles is high so it moves into the blood stream to be transported to the lungs and exhaled Robert Malpeli - Balwyn High School 2010

Robert Malpeli - Balwyn High School 2010 ↑ Arterio-venous oxygen difference (a-vO2 diff) The greater the extraction of oxygen by working muscles, the greater the a-vO2 diff During exercise, the working muscles extract greater Amounts of oxygen from the blood, increasing the A-vO2 difference. Difference in oxygen concentration in the arteries Compared with the veins. It’s a measure of how much Oxygen the muscles have extracted. Robert Malpeli - Balwyn High School 2010

Changes occurring to aVO2-Diff during exercise The arterio-venous oxygen difference (a-vO2 diff) represents the difference in concentration of oxygen in the arterial blood and the concentration of oxygen in the venous blood. It reflects the amount of oxygen used or extracted by the muscles. The arterio-venous oxygen difference (a-vO2 diff) will increase during exercise as working muscles extract more oxygen from the blood into the muscle to produce aerobic energy during exercise – up to 75% more than at rest.

Blood Lactate levels during sub-maximal and maximal intensities Blood lactate levels will be lower during sub-maximal physical activity as compared to maximal exercise where the level of blood lactate will be higher. This because during sub-maximal activity, the athlete is relying primarily on the aerobic system at this intensity. This results in little production of lactate and lactate levels in the blood remain low. When exercise intensity increases to maximal levels the athlete is relying on the anaerobic systems and this results in the production of increased amounts of lactate. This then enters the blood and blood lactate levels begin to rise as the rate of lactate production begins to exceed the rate at which lactate can be removed from the blood and will begin to accumulate in the body.

Blood Redistribution Blood is preferentially redistributed around the body to the working muscles to supply more oxygen and nutrients to assist in aerobic energy production. If the body starts to get too hot, blood will begin to be redistributed away from the working muscles to the surface of the skin to assist with cooling the body (thermoregulation).

Stroke Volume during sub-maximal and maximal intensities Stroke volume plateaus during sub-maximal activity at approximately 40-60% of maximal exercise capacity. Stroke volume plateaus at this exercise intensity because there is insufficient time for further filling of the ventricle as a result of simultaneous increases in heart rate.

Interplay between the body systems allowing increases in oxygen uptake to occur As physical activity begins, the working muscles require more oxygen to produce energy. The cardiovascular system and respiratory system work together to deliver more oxygen to the working muscles via increases in heart rate, stroke volume, cardiac output, arterio-venous difference, respiratory rate, tidal volume and ventilation to deliver more oxygen, whilst the muscles themselves work to utilise the additional oxygen made available.