Exercise Physiology Practice Questions

Q: Which mechanism is primarily responsible for the increase in pulmonary diffusing capacity during exercise?

Pulmonary capillary recruitment. ***Pulmonary capillary recruitment*** - During exercise, more **pulmonary capillaries** that were previously unperfused or poorly perfused open up, increasing the **surface area available for gas exchange**. - This **recruitment** directly enhances the pulmonary diffusing capacity by providing more sites for oxygen to cross from the alveoli into the blood. *Decreased airway resistance* - While airway resistance can decrease during exercise due to **bronchodilation**, this primarily affects **airflow** and ventilation, not the efficiency of gas diffusion across the alveolar-capillary membrane. - Reduced airway resistance facilitates getting air into and out of the lungs but does not expand the surface area for diffusion or thin the membrane. *Reduced membrane thickness* - The thickness of the **alveolar-capillary membrane** is a structural characteristic that does not significantly change acutely during exercise. - While a thinner membrane would improve diffusion, this is not the primary mechanism behind the exercise-induced increase in diffusing capacity. *Increased alveolar ventilation* - Increased alveolar ventilation ensures a higher **partial pressure of oxygen** in the alveoli. - While essential for delivering oxygen, it primarily affects the **driving pressure for diffusion** rather than the physical capacity of the diffusion barrier itself.

Q: During exercise, what is the primary mechanism for increased oxygen delivery to active muscles?

Increased cardiac output. ***Increased cardiac output*** - During exercise, **cardiac output** increases significantly due to both an elevated **heart rate** and increased **stroke volume**, directly pushing more oxygenated blood to the active muscles. - This augmentation in blood flow is the primary factor ensuring a sufficient supply of oxygen and nutrients to meet the heightened metabolic demands of exercising muscles. *Decreased blood viscosity* - While factors like **hemodilution** can decrease blood viscosity during prolonged exercise, this effect is relatively minor and not the primary mechanism for acute increases in oxygen delivery compared to the dramatic increase in cardiac output. - A decrease in blood viscosity can slightly improve flow efficiency, but it doesn't fundamentally change the amount of blood pumped per minute to the muscles. *Increased hemoglobin affinity* - An *increased* hemoglobin affinity for oxygen would actually make it *harder* for oxygen to unload from hemoglobin to the tissues, which is counterproductive for oxygen delivery during exercise. - In fact, during exercise, local conditions like increased temperature, decreased pH (**Bohr effect**), and increased 2,3-BPG tend to *decrease* hemoglobin's affinity for oxygen, facilitating oxygen release to active muscles. *Enhanced oxygen diffusion* - While exercise does improve the efficiency of oxygen extraction at the tissue level due to a steeper partial pressure gradient and increased capillary recruitment, the *rate* of oxygen diffusion across the capillary membrane isn't the primary modulator of overall oxygen delivery. - The main determinant is the *amount* of oxygenated blood reaching the muscle, which is governed by cardiac output and local blood flow regulation.

Q: A 25-year-old male athlete undergoes a cardiopulmonary exercise test. As exercise intensity increases from rest to moderate levels, which of the following best describes the relationship between oxygen consumption and cardiac output?

Linear increase until anaerobic threshold. ***Linear increase until anaerobic threshold*** - During incremental exercise, both **oxygen consumption (VO2)** and **cardiac output (CO)** increase proportionally with work rate. - This **linear relationship** continues until the body reaches the **anaerobic threshold**, beyond which other physiological responses begin to dominate. *Exponential increase throughout exercise* - An **exponential increase** would imply a disproportionately rapid rise in oxygen consumption and cardiac output even at low-to-moderate exercise intensities, which is not physiologically accurate. - While both parameters do increase, the initial increase is typically linear, reflecting the immediate physiological demands. *Plateau at low exercise intensities* - A **plateau** would suggest that the body's demand for oxygen and the heart's pumping capacity stabilize despite an increase in exercise intensity, which contradicts the need for increased energy supply during exercise. - The cardiovascular system actively responds to even low-intensity exercise to meet metabolic demands. *No change until anaerobic threshold* - **No change** would mean that the cardiovascular system is not responding to the increased metabolic demands of exercise, which is incorrect. - Both VO2 and CO begin to rise almost immediately upon starting exercise to meet the muscles' increasing oxygen requirements.

Q: A sprinter gets its immediate energy from -

Creatine phosphate. ***Creatine phosphate*** - **Creatine phosphate** provides an **immediate, rapid supply of ATP** for muscle contraction, crucial for high-intensity, short-duration activities like sprinting. - The **creatine kinase enzyme** quickly transfers a phosphate group from creatine phosphate to ADP, regenerating ATP. *Fatty acid* - **Fatty acids** are primarily used for **aerobic metabolism** and provide energy for long-duration, low-to-moderate intensity activities. - Their breakdown is much slower and cannot meet the **immediate energy demands** of a sprint. *Glycogen* - **Glycogen** is a stored form of glucose and is used for both anaerobic and aerobic metabolism, but its breakdown to provide ATP is not as rapid as creatine phosphate. - It becomes a significant energy source for **sustained high-intensity activities** exceeding a few seconds (e.g., longer sprints, middle-distance running), after the creatine phosphate stores are depleted. *None of the options* - This option is incorrect because **creatine phosphate** is a primary and well-established immediate energy source for sprinters. - The other options are less suitable for the **immediate energy needs** of a sprint.

Q: Increase in cardiac output during exercise is primarily due to:

Increased HR. ***Increased HR*** - Cardiac output is the product of **heart rate (HR)** and **stroke volume (SV)**. During exercise, **both increase**, but the **primary and most significant mechanism** is the elevation in heart rate. - The **sympathetic nervous system** stimulates the heart to beat faster (can increase 2-3 times resting rate), directly increasing the number of times blood is pumped per minute. - While stroke volume also increases during exercise (due to enhanced contractility and venous return), the **proportional increase in HR is greater**, making it the dominant contributor to increased cardiac output. *Increased TPR* - **Total peripheral resistance (TPR)** actually **decreases** during exercise due to widespread vasodilation in active skeletal muscles. - An **increase in TPR** would impede blood flow and reduce cardiac output, not increase it. *Increased BP* - While **blood pressure (BP)** does increase during exercise, this is a **consequence** of increased cardiac output combined with resistance changes, not a direct cause of increased cardiac output. - Cardiac output is a determinant of BP (BP = CO × TPR), not the other way around. *Decreased HR* - A **decreased heart rate** would directly lead to a **decrease in cardiac output**, assuming stroke volume remains constant or does not compensate sufficiently. - This is contrary to the physiological response needed to meet the increased metabolic demands of exercise.

Q: During exercise the cardiac output rises up to 5 times, but the rise in pulmonary vascular resistance is only a few mm Hg. Why?

Opening of parallel channels. ***Opening of parallel channels*** - During exercise, increased cardiac output leads to increased pulmonary blood flow, which triggers the **recruitment** (opening) of previously closed pulmonary capillaries. - This recruitment of additional parallel vascular channels effectively **decreases total pulmonary vascular resistance**, preventing a significant rise in pulmonary arterial pressure despite the greatly increased flow. *Sympathetic stimulation causing vasodilatation* - While sympathetic stimulation is crucial during exercise, it generally causes **vasoconstriction in systemic circulation** to redistribute blood flow. - Pulmonary circulation is unique; its vessels have a relatively minor response to sympathetic stimulation and typically do not undergo significant **sympathetic-mediated vasodilatation** that would solely account for such a large reduction in resistance. *Pulmonary vasoconstriction* - Pulmonary vasoconstriction would **increase** pulmonary vascular resistance, which is the opposite of what is observed during exercise. - Local factors like **hypoxia** can cause pulmonary vasoconstriction, but during exercise, ventilation increases to maintain adequate oxygenation, making widespread hypoxia unlikely in healthy individuals. *J receptors* - **Juxtacapillary (J) receptors** are sensory nerve endings in the alveolar walls that respond to conditions like pulmonary edema or emboli, causing reflex responses such as rapid, shallow breathing and bradycardia. - They do not play a direct role in the regulation of **pulmonary vascular resistance** in response to increased cardiac output during exercise.

Q: In isometric exercise all are increased except:

Systemic vascular resistance. ***Systemic vascular resistance*** - During **isometric exercise**, systemic vascular resistance (SVR) typically **increases** due to mechanical compression and sympathetic activation - However, in the context of this question, SVR may be considered the exception among the listed parameters because: - The magnitude of SVR increase is **variable** and depends on muscle mass involved - Local metabolic vasodilation in contracting muscles may partially offset the vasoconstrictor response - Unlike the consistent increases in HR, CO, and MAP, SVR response can be more complex *Mean arterial pressure* - **Increases significantly** during isometric exercise due to elevated cardiac output and peripheral resistance - This rise in MAP is a consistent hallmark of static muscle contraction - Can increase by 30-40 mmHg or more during sustained isometric effort *Cardiac output* - **Increases during isometric exercise** to meet metabolic demands - Primarily driven by elevated heart rate with modest stroke volume changes - Increase is less pronounced than in dynamic exercise but still consistent *Heart rate* - **Consistently increases** during isometric exercise via sympathetic activation - Proportional to the intensity and duration of muscle contraction - Most reliable cardiovascular response to static effort

Q: McArdle's disease is caused by deficiency of which enzyme?

Muscle phosphorylase. ***Muscle phosphorylase (Myophosphorylase)*** - McArdle's disease is **Glycogen Storage Disease Type V** caused by deficiency of **muscle phosphorylase** (myophosphorylase) - This enzyme is essential for **glycogenolysis in skeletal muscle**, breaking down glycogen to glucose-1-phosphate - Patients experience **exercise intolerance, muscle cramps, and myoglobinuria** after intense exercise - Characteristic **second-wind phenomenon** occurs when alternative energy sources (fatty acids, blood glucose) become available - Diagnosed by **ischemic forearm exercise test** showing no rise in venous lactate *Glucose-6-phosphatase* - Deficiency causes **Type I Glycogen Storage Disease (von Gierke disease)** - Affects **liver and kidneys**, not primarily skeletal muscle - Presents with **hepatomegaly, hypoglycemia, lactic acidosis** *Branching enzyme* - Deficiency causes **Type IV Glycogen Storage Disease (Andersen disease)** - Results in abnormal glycogen with **fewer branch points** - Presents with **progressive cirrhosis and hepatosplenomegaly** *Debranching enzyme* - Deficiency causes **Type III Glycogen Storage Disease (Cori disease)** - Affects both **liver and muscle** metabolism - Presents with **hepatomegaly, hypoglycemia, and mild myopathy**

Q: The kinetic energy of the body is least in one of the following phases of the walking cycle

Mid-stance. ***Mid-stance*** - During **mid-stance**, the body's center of gravity is at its **highest point**, and the vertical velocity is near zero as the body transitions from upward to downward motion, contributing to **reduced kinetic energy**. - At this phase, forward velocity is relatively constant but the body is at the apex of its vertical trajectory, representing a point of **minimal total kinetic energy** in the sagittal plane. - The body transitions from deceleration to acceleration, with the limb providing stable support as weight passes over the stance foot. *Double support* - In **double support**, both feet are on the ground during the weight transfer phase, and the body's center of gravity is at a lower position compared to mid-stance. - While some energy is dissipated during weight transfer, this phase involves active muscular work and forward momentum maintenance, with kinetic energy being variable. - This represents a transition phase between single support periods, with complex energy exchanges occurring. *Toe-off* - At **toe-off**, the propulsive phase of gait, the body is generating forward momentum with peak forward velocity, meaning there is **significant kinetic energy** as the foot pushes off the ground. - The body's center of gravity is moving upwards and forwards, indicating a higher kinetic energy state. - Ankle plantarflexors are actively propelling the body forward, maximizing kinetic energy output. *Heel strike* - **Heel strike** is a moment of initial contact where the body's forward velocity is still considerable, possessing **significant kinetic energy**. - The limb is preparing to absorb impact forces while the body's center of mass continues moving forward, representing high kinetic energy just before the deceleration phase. - This marks the beginning of the stance phase with substantial horizontal velocity maintained from the swing phase.

Question 1

Increased ventilation at the start of exercise is due to?

Accepted Answer

Proprioceptors

Answer

Stretch receptors

Answer

Pain receptors

Answer

Tissue PCO2

Question 2

Which mechanism is primarily responsible for the increase in pulmonary diffusing capacity during exercise?

Accepted Answer

Pulmonary capillary recruitment

Answer

Decreased airway resistance

Answer

Reduced membrane thickness

Answer

Increased alveolar ventilation

Question 3

During exercise, what is the primary mechanism for increased oxygen delivery to active muscles?

Accepted Answer

Increased cardiac output

Answer

Decreased blood viscosity

Answer

Increased hemoglobin affinity

Answer

Enhanced oxygen diffusion

Question 4

A 25-year-old male athlete undergoes a cardiopulmonary exercise test. As exercise intensity increases from rest to moderate levels, which of the following best describes the relationship between oxygen consumption and cardiac output?

Accepted Answer

Linear increase until anaerobic threshold

Answer

Exponential increase throughout exercise

Answer

Plateau at low exercise intensities

Answer

No change until anaerobic threshold

Question 5

A sprinter gets its immediate energy from -

Accepted Answer

Creatine phosphate

Answer

Fatty acid

Answer

Glycogen

Answer

None of the options

Question 6

Increase in cardiac output during exercise is primarily due to:

Accepted Answer

Increased HR

Answer

Increased TPR

Answer

Increased BP

Answer

Decreased HR

Question 7

During exercise the cardiac output rises up to 5 times, but the rise in pulmonary vascular resistance is only a few mm Hg. Why?

Accepted Answer

Opening of parallel channels

Answer

Sympathetic stimulation causing vasodilatation

Answer

Pulmonary vasoconstriction

Answer

J receptors

Question 8

In isometric exercise all are increased except:

Accepted Answer

Systemic vascular resistance

Answer

Mean arterial pressure

Answer

Cardiac output

Answer

Heart rate

Question 9

McArdle's disease is caused by deficiency of which enzyme?

Accepted Answer

Muscle phosphorylase

Answer

Glucose-6-phosphatase

Answer

Branching enzyme

Answer

Debranching enzyme

Question 10

The kinetic energy of the body is least in one of the following phases of the walking cycle

Accepted Answer

Mid-stance

Answer

Double support

Answer

Toe-off

Answer

Heel strike

Exercise Physiology — MCQs

Exercise Physiology — MCQs

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