Exercise Physiology — MCQs

Exercise Physiology Indian Medical PG Practice Questions and MCQs

Question 51: Immediate soreness and fatigue in muscles during vigorous exercise is primarily due to?

A. Lactic acidosis (Correct Answer)
B. Hyponatremia
C. Hyperthermia
D. Hyperkalemia

Explanation: ***Lactic acidosis*** - During **vigorous exercise**, oxygen supply to muscles may be insufficient, leading to anaerobic metabolism and the accumulation of **lactic acid**. - This buildup of **lactic acid** lowers pH within muscle cells, which interferes with muscle contraction and causes immediate soreness and fatigue. *Hyponatremia* - **Hyponatremia** is a condition of low sodium concentration in the blood, often associated with prolonged, excessive fluid intake without adequate electrolyte replacement. - While it can cause muscle cramps and weakness, it typically manifests in **endurance events** (e.g., marathons) rather than immediate symptoms during vigorous exercise. *Hyperthermia* - **Hyperthermia** is an elevated body temperature due to overwhelmed thermoregulatory mechanisms, often seen in hot environments or prolonged intense activity. - It can lead to fatigue, weakness, and dizziness, but widespread immediate muscle soreness is more directly linked to **metabolic byproducts** rather than solely heat. *Hyperkalemia* - **Hyperkalemia** refers to elevated potassium levels in the blood, which can affect cardiac and neuromuscular function. - While it can lead to muscle weakness or paralysis, it is not a primary or immediate cause of post-exercise muscle soreness or fatigue in healthy individuals during typical vigorous exercise.

Question 52: Which of the following is the mechanism for a decrease in splanchnic blood flow during exercise?

A. Increased splanchnic metabolic demand
B. Arteriolar vasoconstriction due to sympathetic stimulation (Correct Answer)
C. Arteriolar vasodilation due to parasympathetic stimulation
D. Decreased cardiac output to splanchnic organs

Explanation: ***Arteriolar vasoconstriction due to sympathetic stimulation*** - During **exercise**, the **sympathetic nervous system** is activated, leading to a release of **norepinephrine** and **epinephrine**. These neurotransmitters bind to **alpha-1 adrenergic receptors** on **splanchnic arterioles**, causing **vasoconstriction**. - This **vasoconstriction** shunts blood away from the gastrointestinal tract, liver, and spleen, redirecting it towards the **skeletal muscles** and heart, which have a higher metabolic demand during exercise. *Increased splanchnic metabolic demand* - The **splanchnic organs** (gut, liver, spleen) actually experience a *decrease* in activity and metabolic demand during strenuous exercise, as their primary functions are temporarily reduced. - An increase in splanchnic metabolic demand would typically lead to **vasodilation** to meet those demands, not a decrease in blood flow. *Arteriolar vasodilation due to parasympathetic stimulation* - **Parasympathetic stimulation** generally causes **vasodilation** in the gut and is primarily active during rest and digestion. - During exercise, **parasympathetic activity** is *reduced*, and **sympathetic activity** predominates, leading to **vasoconstriction**, not vasodilation. *Decreased cardiac output to splanchnic organs* - While the *proportion* of **cardiac output** directed to splanchnic organs decreases during exercise, the overall **cardiac output** *increases* significantly. - The reduction in splanchnic blood flow is a result of **active vasoconstriction** and blood redistribution, not a direct decrease in total cardiac output itself, which is actually elevated.

Question 53: Least useful for a 800-m run in a competitive event would be

A. Lohmann reaction (Correct Answer)
B. Pale muscle fibres
C. Muscle glycogen
D. Oxidative phosphorylation

Explanation: ***Lohmann reaction*** - The **Lohmann reaction** (creatine kinase reaction) is primarily involved in rapid, **short-burst energy production** for activities lasting a few seconds (e.g., sprints). - An 800-meter run is a middle-distance event requiring sustained energy from both anaerobic and aerobic pathways, where the immediate **phosphocreatine** system (Lohmann reaction) is quickly depleted and less useful for the majority of the race. *Pale muscle fibres* - **Pale muscle fibers** (Type II or fast-twitch fibers) are characterized by a high capacity for **anaerobic metabolism** and rapid, powerful contractions. - While they are crucial for the initial burst and speed in an 800-m run, their high glycolytic capacity makes them essential for the sustained high-intensity effort required, even as the race progresses beyond pure sprint. *Muscle glycogen* - **Muscle glycogen** is the primary stored carbohydrate fuel for **anaerobic glycolysis**, which is a significant energy pathway during the high-intensity portions of an 800-m run. - Its breakdown provides quick ATP generation without oxygen, supporting the rapid pace required throughout much of the race. *Oxidative phosphorylation* - **Oxidative phosphorylation** (aerobic respiration) becomes increasingly important as an 800-m race progresses, contributing a substantial portion of the ATP required for sustained muscle contraction. - It allows for the efficient production of large amounts of ATP when oxygen is available, crucial for maintaining pace and minimizing fatigue over the middle distance.

Question 54: For a person who is running, the main source of energy used in the first minute is:

A. Fat
B. Glucose
C. Glycogen (Correct Answer)
D. Phosphagen

Explanation: ***Glycogen*** - For intense activities like running, especially in the first minute, the body primarily relies on **anaerobic metabolism** and readily available glucose stored as glycogen in muscles and the liver. - **Glycogenolysis** rapidly breaks down glycogen into glucose, which then enters glycolysis to produce ATP quickly, albeit inefficiently without oxygen. *Fat* - **Fat (triglycerides)** is a primary energy source for prolonged, lower-intensity exercise, as its breakdown via **beta-oxidation** and subsequent **oxidative phosphorylation** is slower and requires oxygen. - While fat provides more ATP per gram, its utilization is not as immediate as glycogen for high-intensity, short-duration efforts. *Glucose* - **Glucose** in the bloodstream is an immediate fuel source, but its supply is limited and quickly supplemented by **glycogenolysis** during intense exercise. - While glucose is the molecule ultimately catabolized for energy, it's primarily derived from glycogen stores rather than circulating glucose for the initial burst of high-intensity activity. *Phosphagen* - The **phosphagen system (creatine phosphate)** provides energy for extremely short, maximal bursts of effort (e.g., first 10-15 seconds of a sprint) by rapidly regenerating ATP. - While crucial for the very initial phase, its stores are depleted quickly and cannot sustain energy production for an entire minute of running.

Question 55: Blood supply to the brain during moderate exercise:

A. Fluctuates unpredictably
B. Increases
C. Decreases
D. Remains constant (Correct Answer)

Explanation: ***Correct: Remains constant*** - Cerebral blood flow is **autoregulated** to ensure a stable supply of oxygen and nutrients to the brain, regardless of changes in systemic blood pressure or metabolic demand during moderate exercise. - This autoregulation mechanism maintains a relatively constant blood flow (~750 mL/min or 50 mL/100g brain tissue/min) within a wide range of mean arterial pressures (60-150 mmHg). - The brain receives approximately **15% of cardiac output** at rest, and this proportion is maintained during moderate exercise. *Incorrect: Fluctuates unpredictably* - While there can be minor variations, the brain's **autoregulatory mechanisms** work to stabilize blood flow, preventing unpredictable fluctuations that would harm brain function. - Significant, unpredictable fluctuations would indicate a failure of these crucial physiological controls. *Incorrect: Increases* - Though overall cardiac output increases during exercise, the brain's demand for blood flow does **not significantly increase** in proportion to the body's other organs. - The brain prioritizes a constant, rather than an increased, supply to maintain stable function during moderate exercise. *Incorrect: Decreases* - A decrease in cerebral blood flow would lead to **cerebral hypoperfusion**, compromising brain function and potentially causing symptoms like dizziness or syncope. - The body's physiological responses during exercise are designed to prevent such a dangerous outcome.

Question 56: Why does the body produce sweat during exercise?

A. Regulate temperature (Correct Answer)
B. Maintain pH
C. Improve circulation
D. Eliminate toxins

Explanation: **Regulate temperature** - Sweating is a primary mechanism for **thermoregulation**, allowing the body to cool down by evaporating water from the skin surface. - During exercise, **muscle activity generates heat**, raising the body's core temperature, which triggers the sweating response. *Maintain pH* - The body maintains pH primarily through **buffer systems** in the blood, the **respiratory system**, and the **renal system**. - While sweat has a slightly acidic pH (typically between 4.0 and 6.0), its role in systemic pH balance is negligible compared to other homeostatic mechanisms. *Improve circulation* - Exercise itself improves circulation through **increased heart rate** and **vasodilation**, delivering more oxygen and nutrients to muscles. - Sweating does not directly improve circulation; rather, it is a response to the physiological demands and heat generated by improved circulation during exercise. *Eliminate toxins* - The primary organs for **eliminating toxins** are the **liver** (metabolism) and the **kidneys** (excretion in urine). - While sweat contains small amounts of metabolic waste products, its contribution to detoxification is minimal and not its primary function.

Question 57: During intense exercise, the body's demand for oxygen increases. What are the physiological mechanisms that enhance oxygen delivery to the muscles?

A. Increased cardiac output and increased peripheral resistance, with decreased respiratory rate and depth
B. Increased cardiac output and decreased peripheral resistance (Correct Answer)
C. Decreased cardiac output and increased peripheral resistance, with decreased oxygen extraction by muscles
D. Decreased cardiac output and decreased peripheral resistance, with increased blood flow to inactive muscles

Explanation: ***Increased cardiac output and decreased peripheral resistance*** - During intense exercise, **cardiac output increases** significantly to pump more oxygenated blood to the working muscles. - **Peripheral resistance decreases** due to vasodilation in the active muscles, improving blood flow. *Increased cardiac output and increased peripheral resistance, with decreased respiratory rate and depth* - While **cardiac output increases**, **peripheral resistance does not increase** globally; instead, it decreases in active muscles to facilitate blood flow. - A **decreased respiratory rate and depth** would hinder oxygen uptake and delivery, which contradicts the body's need during intense exercise. *Decreased cardiac output and increased peripheral resistance, with decreased oxygen extraction by muscles* - A **decreased cardiac output** would limit oxygen delivery to the muscles, which is contrary to the body's response during intense exercise. - **Decreased oxygen extraction by muscles** would also reduce oxygen availability, impairing performance. *Decreased cardiac output and decreased peripheral resistance, with increased blood flow to inactive muscles* - **Decreased cardiac output** would not meet the increased oxygen demand of active muscles. - **Increased blood flow to inactive muscles** would divert blood away from working muscles, reducing their oxygen supply.

Question 58: A 24-year-old athlete collapses during a marathon. His core temperature is elevated at 40°C, and he is experiencing confusion. Which mechanism is primarily responsible for his hyperthermia?

A. Increased basal metabolic rate
B. Increased muscular activity (Correct Answer)
C. Decreased sweat production
D. Increased ambient temperature

Explanation: ***Increased muscular activity*** - During intense exercise like a marathon, **skeletal muscles generate a significant amount of heat** as a byproduct of ATP hydrolysis. - This heat production can overwhelm the body's cooling mechanisms, leading to a rapid rise in **core temperature** and hyperthermia. *Increased basal metabolic rate* - **Basal metabolic rate** refers to the energy expended at rest, which does not significantly increase to cause severe hyperthermia during exercise. - While exercise does increase metabolic rate, it's the specific heat generated by muscle contraction that is the primary driver of hyperthermia in this context, not an elevated basal rate. *Decreased sweat production* - Although **decreased sweat production** would exacerbate hyperthermia, it is generally a compensatory mechanism or a sign of dehydration, not the primary cause of heat generation itself. - In exertional heatstroke, the body is usually sweating profusely initially, but this mechanism may fail due to dehydration or environmental factors. *Increased ambient temperature* - While a **high ambient temperature** can contribute to the body's inability to dissipate heat effectively, it is a confounding factor, not the primary mechanism of heat generation in an exercising individual. - The internal heat produced by muscular activity is the direct source of the core temperature elevation described.

Question 59: Which of the following is the MOST accurate statement regarding the regulation of blood flow during exercise?

A. Muscle blood flow increases. (Correct Answer)
B. Coronary blood flow remains stable during exercise.
C. Blood flow to the gut remains unchanged during exercise.
D. Total peripheral resistance increases during exercise.

Explanation: ***Muscle blood flow increases*** - During exercise, **skeletal muscles** have a significantly *increased metabolic demand* for oxygen and nutrients, leading to **vasodilation** and a substantial increase in blood flow. - This augmentation in blood flow is crucial for meeting the heightened requirements of contracting muscles and is mediated by both **local metabolic factors** and sympathetic nervous system activity. *Coronary blood flow remains stable during exercise.* - **Coronary blood flow** actually *increases significantly* during exercise to meet the **heightened metabolic demands of the myocardium**, which pumps harder and faster. - This increase is vital to ensure the heart muscle itself receives enough oxygen and nutrients to sustain its increased workload. *Blood flow to the gut remains unchanged during exercise.* - **Blood flow to the gastrointestinal tract** actually *decreases dramatically* during exercise as blood is *redistributed away from splanchnic organs* towards working muscles. - This **sympathetic vasoconstriction** in the gut helps to shunt blood to areas of higher metabolic need. *Total peripheral resistance increases during exercise.* - **Total peripheral resistance (TPR)** usually *decreases* during dynamic exercise due to widespread **vasodilation in active skeletal muscles**, despite vasoconstriction in other areas. - The *increased cardiac output* combined with *decreased TPR* allows for a massive increase in blood flow to meet the muscles' demands.

Question 60: During moderate exercise, cardiac output increases. What is the primary physiological mechanism responsible for this increase?

A. Increased heart rate (Correct Answer)
B. Increased blood viscosity
C. Increased blood pressure
D. Increased peripheral resistance

Explanation: ***Increased heart rate*** - During moderate exercise, cardiac output increases through **both increased heart rate and increased stroke volume**, but heart rate typically shows the **more pronounced and immediate response**. - The elevation in heart rate is driven by **sympathetic nervous system activation** and **reduced parasympathetic tone**, leading to more cardiac cycles per minute. - While stroke volume also increases (via the Frank-Starling mechanism, increased contractility, and enhanced venous return), the **heart rate increase is more dramatic** during moderate exercise, often doubling from rest values. - This makes increased heart rate the **primary contributor** to the overall rise in cardiac output during moderate-intensity exercise. *Increased blood viscosity* - **Increased blood viscosity** would actually **impair blood flow** and reduce cardiac output by increasing resistance to flow. - The heart would need to work harder against increased viscosity, which would decrease, not increase, cardiac efficiency. - While hemoconcentration from dehydration can occur during prolonged exercise, this is not a mechanism that increases cardiac output. *Increased blood pressure* - Blood pressure does increase during exercise, but this is a **consequence** of increased cardiac output and altered peripheral resistance, not the **cause** of increased cardiac output. - Blood pressure = Cardiac Output × Total Peripheral Resistance; increased pressure alone does not drive increased output. - The pressure rise reflects the cardiovascular response to exercise rather than being the mechanism for increasing cardiac output. *Increased peripheral resistance* - **Increased peripheral resistance** would actually **oppose** cardiac output and make it harder for the heart to pump blood. - During exercise, total peripheral resistance actually **decreases** due to marked vasodilation in working skeletal muscles, which overrides vasoconstriction in non-active tissues. - This reduced resistance facilitates, rather than causes, the increase in cardiac output to exercising muscles.

Practice by Chapter

Energy Systems in Exercise

Practice Questions

Cardiovascular Responses to Exercise

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Respiratory Adaptations to Exercise

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Muscle Metabolism During Exercise

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Neuromuscular Adaptations to Training

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Exercise in Hot and Cold Environments

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Fatigue Mechanisms

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Recovery Processes

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Training Principles and Adaptations

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Exercise Testing and Prescription

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