Exercise Physiology: Acute Responses - Anatomy and Physiology
- Roughly how much does cardiac output rise from rest to maximal exercise in a healthy untrained adult?
- About four- to fivefold, from about 5 L/min at rest to about 20 to 25 L/min.
- During exercise, oxygen consumption is 1500 mL/min and the arteriovenous O2 difference is 15 mL O2 per 100 mL blood. What is cardiac output?
- 10 L/min. By the Fick principle, cardiac output = 1500 mL/min divided by 150 mL O2 per liter of blood.
- What is the lactate threshold?
- The exercise intensity at which blood lactate begins to rise sharply because production exceeds clearance.
- How does the arteriovenous oxygen difference change during exercise?
- It widens, because active muscle extracts a larger share of the oxygen from each volume of blood.
- During dynamic exercise such as running, how do systolic and diastolic blood pressure change?
- Systolic pressure rises substantially, while diastolic pressure stays about the same or falls slightly because active muscle vessels dilate.
- During intense exercise, which abdominal organs receive markedly reduced blood flow?
- The digestive organs and the kidneys, through sympathetic vasoconstriction, freeing blood for active muscle.
- Which local chemical changes in active skeletal muscle cause its arterioles to dilate?
- Increased CO2, H+, K+, and adenosine, decreased O2, and higher temperature.
- During moderate exercise, how does minute ventilation mainly increase at first?
- Mainly through a larger tidal volume; breathing rate rises more as intensity increases.
- What causes heart rate to rise within seconds of starting exercise, before metabolites accumulate?
- Withdrawal of parasympathetic (vagal) tone and central command from the brain, followed by sympathetic activation.
- How does total peripheral resistance change during dynamic whole-body exercise?
- It decreases, because metabolic vasodilation in active skeletal muscle outweighs vasoconstriction elsewhere.
- How does stroke volume respond as exercise intensity increases?
- It rises, from greater venous return (muscle pump) and sympathetic contractility, then plateaus at moderate intensity in most people.