Cardiovascular and Respiratory Responses to Exercise
Blood Flow Redistribution during Exercise
Exercising Muscles: Experience significant vasodilation. This occurs because local intrinsic mechanisms within the exercising muscles override sympathetic vasoconstriction, allowing for increased blood flow.
Impact on a-vO2 Difference: The redistribution of blood flow profoundly affects the arterial-venous oxygen difference. More blood directed to active tissues means greater oxygen utilization, leading to a higher a-vO2 difference. Athletes skilled at this redistribution show a significantly greater a-vO_2 difference.
Exercise in the Heat (Skin Blood Flow):
When exercising in heat, blood is shunted to the skin for vasodilation, aiding in cooling the body.
Negative Effects on a-vO_2 Difference:
Reduced Muscle Oxygen Use: Less blood goes to the muscles, limiting their oxygen uptake.
Reduced Venous Return: Blood tends to pool in the skin vessels, slowing its return to the heart. Blood returning from muscles is more easily pushed back, so shunting to the skin impairs this process.
Performance Impairment: Exercising in the heat often compromises VO_{2max}, leading to impaired performance due to these effects.
Cardiac Direct and Cardiovascular Drift
Steady State Heart Rate: Defined as the heart rate plateau reached after a certain period of exercise at a consistent intensity, where oxygen consumption matches demand.
Oxygen Requirement vs. Consumption: For a given exercise intensity (e.g., running at 6 miles/hour), there's a specific oxygen requirement.
O2 Deficit: The lag between the start of exercise and when actual oxygen consumption meets the body's demand for that activity. During this time, the body isn't getting enough oxygen because heart rate, stroke volume, and a-vO_2 difference haven't fully risen to the required level.
O2 Debt (EPOC - Excess Post-exercise Oxygen Consumption): After exercise, heart rate and breathing rate remain elevated for a period. This