Exercise Physiology — MCQs
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Which of the following is caused by exercise?
On vigorous exercise, which of the following is most critical for sustaining respiratory function?
As part of a research experiment, a person undergoes two fine needle muscle biopsies to obtain small amounts of tissue for biochemical analysis. The first is taken at the beginning of the experiment while the subject is at rest. The second is taken at the end of 30 minutes of aerobic exercise on a stationary bicycle. The activity of the muscle pyruvate dehydrogenase complexes is found to be much higher in the second measurement. Which of the following biochemical changes would be most likely to produce this effect?
What type of exercise is done to increase muscle strength?
Severe muscular exercise causes which of the following?
During exercise, which of the following is decreased?
Which of the following changes is noted during exercise?
What physiological changes occur during exercise?
A manual laborer moves from Kashmir to Delhi in March and works outdoors for a month. Compared with his responses on the first few days in Delhi, for the same activity level after acclimatization, what would one expect?
Which of the following is NOT a mechanism that increases blood supply to muscles during exercise?
Exercise Physiology Indian Medical PG Practice Questions and MCQs
Question 11: Which of the following is caused by exercise?
- A. Increased blood flow to the muscles after half a minute or one minute
- B. Increase in cerebral blood flow due to an increase in systolic blood pressure
- C. Increase in body temperature (Correct Answer)
- D. Decreased O2 consumption
Explanation: **Explanation:** **Correct Option: C. Increase in body temperature** During exercise, muscle contraction involves the conversion of chemical energy (ATP) into mechanical work. However, this process is only about 20-25% efficient; the remaining 75-80% of energy is released as **heat**. This metabolic heat production leads to a rise in core body temperature, which can reach 38°C to 40°C (100°F to 104°F) during vigorous activity. This rise triggers thermoregulatory mechanisms like sweating and cutaneous vasodilation. **Analysis of Incorrect Options:** * **A. Increased blood flow to the muscles after half a minute:** This is incorrect because the increase in blood flow is **immediate**. At the onset of exercise, "command signals" from the brain and local vasodilator metabolites (like K+, adenosine, and lactate) cause an almost instantaneous rise in muscle perfusion. * **B. Increase in cerebral blood flow:** Cerebral blood flow is remarkably **constant** due to powerful autoregulation. While systolic blood pressure rises during exercise, cerebral vessels constrict or dilate to maintain steady flow, preventing hypertensive damage or ischemia. * **D. Decreased O2 consumption:** Exercise significantly **increases** oxygen consumption ($VO_2$) to meet the high metabolic demands of active muscles. **High-Yield Pearls for NEET-PG:** * **$VO_2$ Max:** The best indicator of aerobic cardiovascular fitness. * **Blood Flow Redistribution:** During exercise, blood flow to the GI tract and kidneys decreases (via sympathetic vasoconstriction), while flow to the heart and skeletal muscles increases. * **Hemoglobin-Dissociation Curve:** Exercise shifts the curve to the **right** (due to increased $CO_2$, $H^+$, and temperature), facilitating O2 unloading at the tissues (Bohr Effect).
Question 12: On vigorous exercise, which of the following is most critical for sustaining respiratory function?
- A. Availability of ADP
- B. Availability of substrate for ATP production
- C. Glycogen stores (Correct Answer)
- D. Increased intrapleural pressure
Explanation: During **vigorous exercise**, the body’s metabolic demand increases exponentially. To sustain respiratory function (specifically the continuous contraction of the diaphragm and intercostal muscles), a constant supply of energy is required. **Why Glycogen stores is the correct answer:** The primary limiting factor for prolonged, high-intensity (vigorous) muscular activity is the availability of energy substrates. While the body uses various fuels, **muscle glycogen** is the most critical and preferred substrate for rapid ATP production via both aerobic and anaerobic glycolysis. Once glycogen stores are depleted (a phenomenon known as "hitting the wall"), the muscles cannot maintain the force of contraction required for vigorous ventilation, leading to respiratory fatigue. **Analysis of Incorrect Options:** * **A. Availability of ADP:** ADP is a byproduct of ATP hydrolysis. While it acts as a signal to stimulate oxidative phosphorylation, it is never a limiting factor; rather, the rate-limiting step is the regeneration of ATP from ADP. * **B. Availability of substrate for ATP production:** This is a broad term. While technically true, "Glycogen stores" is the **most specific** and physiologically accurate answer in the context of vigorous exercise, as free glucose or fatty acids cannot be mobilized fast enough to meet the peak demands of vigorous activity. * **C. Increased intrapleural pressure:** Intrapleural pressure actually becomes **more negative** (decreases) during inspiration to facilitate air inflow. An increase in intrapleural pressure (becoming positive) occurs during forced expiration but is not a "critical factor" for sustaining function; rather, it is a mechanical consequence. **High-Yield Facts for NEET-PG:** * **Respiratory Quotient (RQ):** During vigorous exercise, the RQ approaches **1.0**, indicating that carbohydrates (glycogen) are the primary fuel source. * **VO2 Max:** This is the best indicator of an individual's aerobic capacity and cardiorespiratory fitness. * **Anaerobic Threshold:** The point during exercise when lactate begins to accumulate significantly in the blood, usually occurring at 50-60% of VO2 max.
Question 13: As part of a research experiment, a person undergoes two fine needle muscle biopsies to obtain small amounts of tissue for biochemical analysis. The first is taken at the beginning of the experiment while the subject is at rest. The second is taken at the end of 30 minutes of aerobic exercise on a stationary bicycle. The activity of the muscle pyruvate dehydrogenase complexes is found to be much higher in the second measurement. Which of the following biochemical changes would be most likely to produce this effect?
- A. Decreased ADP
- B. Decreased intracellular Ca2+
- C. Increased acetyl CoA
- D. Increased pyruvate concentration (Correct Answer)
Explanation: **Explanation:** The **Pyruvate Dehydrogenase (PDH) complex** is the key regulatory enzyme that converts pyruvate into acetyl CoA, linking glycolysis to the TCA cycle. Its activity is tightly regulated by a phosphorylation-dephosphorylation cycle. **Why Option D is Correct:** During aerobic exercise, the rate of glycolysis increases to meet energy demands, leading to an **increase in pyruvate concentration**. Pyruvate acts as a potent **inhibitor of PDH Kinase**. Since PDH Kinase normally phosphorylates (inactivates) the PDH complex, inhibiting the kinase keeps the PDH complex in its **active (dephosphorylated) state**. Thus, increased pyruvate directly promotes PDH activity to ensure efficient aerobic metabolism. **Analysis of Incorrect Options:** * **A. Decreased ADP:** Exercise *increases* ADP levels. High ADP inhibits PDH Kinase, thereby activating PDH. Decreased ADP would have the opposite effect. * **B. Decreased intracellular Ca²⁺:** Exercise *increases* cytosolic Ca²⁺ (released during muscle contraction). Ca²⁺ is a powerful **activator of PDH Phosphatase**, which dephosphorylates and activates the PDH complex. * **C. Increased acetyl CoA:** Acetyl CoA is a product of the PDH reaction. High levels exert **feedback inhibition** by activating PDH Kinase, which shuts down the enzyme complex. **High-Yield NEET-PG Pearls:** * **PDH Regulation:** Active = Dephosphorylated (promoted by PDH Phosphatase); Inactive = Phosphorylated (promoted by PDH Kinase). * **Activators of PDH:** Pyruvate, NAD+, ADP, and **Calcium** (the most important link between muscle contraction and energy production). * **Inhibitors of PDH:** Acetyl CoA, NADH, and ATP (indicators of high energy status). * **Clinical Correlation:** PDH deficiency is a common cause of congenital lactic acidosis, as pyruvate is shunted to lactate when the PDH pathway is blocked.
Question 14: What type of exercise is done to increase muscle strength?
- A. Aerobic isotonic
- B. Isometric
- C. Isotonic (Correct Answer)
- D. All of the above
Explanation: **Explanation:** The correct answer is **Isotonic exercise**. In isotonic (dynamic) exercise, the muscle tension remains constant while the muscle length changes, resulting in joint movement. This type of exercise is the primary method for increasing **muscle strength and hypertrophy**. It involves two phases: concentric (shortening) and eccentric (lengthening), both of which recruit motor units effectively to build contractile proteins. **Analysis of Options:** * **Isotonic (Correct):** By moving a constant load through a range of motion (e.g., weightlifting), the muscle undergoes structural adaptations, increasing the cross-sectional area of fast-twitch fibers, which directly correlates with increased strength. * **Isometric (Incorrect):** In isometric exercise, muscle length remains constant while tension increases (e.g., pushing against a wall). While it improves static endurance and stabilizes joints, it is less effective than isotonic exercise for building overall functional strength and muscle mass. * **Aerobic isotonic (Incorrect):** While aerobic exercises (like jogging) are technically isotonic, they are low-intensity and high-repetition. They primarily increase mitochondrial density and capillary supply (endurance) rather than muscle strength or power. **High-Yield Clinical Pearls for NEET-PG:** * **Isotonic Exercise:** Increases Cardiac Output (CO) primarily by increasing **Stroke Volume**. It causes significant peripheral vasodilation. * **Isometric Exercise:** Causes a disproportionate increase in **Mean Arterial Pressure (MAP)** due to mechanical compression of blood vessels, leading to a significant increase in afterload. * **Hypertrophy vs. Hyperplasia:** Strength training leads to fiber **hypertrophy** (increase in size/actin-myosin filaments), not hyperplasia (increase in number of fibers). * **Muscle Fiber Recruitment:** Strength training primarily targets **Type IIb (Fast-twitch glycolytic)** fibers.
Question 15: Severe muscular exercise causes which of the following?
- A. Lactic acidosis (Correct Answer)
- B. Ketoacidosis
- C. Hypothermia
- D. Increased CPK levels
Explanation: **Explanation:** **Correct Option: A. Lactic Acidosis** During severe or strenuous muscular exercise, the oxygen demand of the skeletal muscles exceeds the oxygen supply (anaerobic threshold). To maintain energy production, muscles switch from aerobic metabolism to **anaerobic glycolysis**. In this pathway, pyruvate is converted into **lactic acid** by the enzyme lactate dehydrogenase (LDH). The accumulation of lactate and hydrogen ions in the bloodstream leads to a decrease in blood pH, resulting in metabolic acidosis (specifically, high anion gap lactic acidosis). **Incorrect Options:** * **B. Ketoacidosis:** This is typically associated with uncontrolled Diabetes Mellitus (DKA) or prolonged starvation, where the body metabolizes fatty acids into ketone bodies. Exercise primarily utilizes glucose and glycogen; it does not trigger ketoacidosis. * **C. Hypothermia:** Exercise generates significant metabolic heat due to muscular contraction. Therefore, severe exercise leads to **hyperthermia** (elevated body temperature), not hypothermia. * **D. Increased CPK levels:** While Creatine Phosphokinase (CPK) levels do rise following intense exercise due to micro-trauma to muscle fibers, **Lactic Acidosis** is the more immediate and physiological hallmark of "severe" exercise metabolism in the context of acid-base balance. In the hierarchy of physiological responses to acute anaerobic exertion, lactic acid production is the definitive metabolic consequence. **High-Yield Facts for NEET-PG:** * **Oxygen Debt:** The extra oxygen consumed after exercise to restore metabolites (ATP, CP, and lactate clearance) to resting levels. * **Bohr Effect:** During exercise, increased $CO_2$, $H^+$ (lactic acid), and temperature shift the Oxygen-Dissociation Curve to the **right**, facilitating oxygen unloading to tissues. * **Respiratory Quotient (RQ):** During severe exercise, the RQ approaches or exceeds 1.0 as carbohydrates become the primary fuel source.
Question 16: During exercise, which of the following is decreased?
- A. Oxidation of fatty acids
- B. Glucagon release
- C. Glycogenolysis
- D. Lipogenesis (Correct Answer)
Explanation: **Explanation:** The physiological response to exercise is driven by the body's need to mobilize energy substrates to meet the increased metabolic demands of skeletal muscles. This is mediated by a shift in the hormonal milieu, primarily characterized by an **increase in sympathetic activity (Catecholamines)** and **Glucagon**, and a **decrease in Insulin**. **Why Lipogenesis is decreased:** Lipogenesis (the synthesis of fatty acids and triglycerides) is an anabolic, energy-storing process stimulated by insulin. During exercise, insulin levels drop and the body enters a catabolic state. High levels of Epinephrine and Glucagon inhibit *Acetyl-CoA Carboxylase*, the rate-limiting enzyme of lipogenesis. Therefore, the body halts fat storage to prioritize fat mobilization. **Analysis of Incorrect Options:** * **Oxidation of fatty acids:** This **increases** during exercise. As glycogen stores deplete, the body relies heavily on Beta-oxidation of free fatty acids (FFAs) to provide ATP for prolonged muscular activity. * **Glucagon release:** This **increases**. The fall in blood glucose and increased sympathetic stimulation during exercise trigger the alpha cells of the pancreas to release glucagon to maintain glycemic levels. * **Glycogenolysis:** This **increases**. Both hepatic and muscle glycogenolysis are rapidly activated (via phosphorylase) to provide immediate glucose for glycolysis. **High-Yield Facts for NEET-PG:** * **Hormonal Shift:** Exercise is "Insulin-like" because it increases GLUT-4 translocation to the sarcolemma via an insulin-independent pathway (AMPK activation). * **Respiratory Quotient (RQ):** During high-intensity exercise, the RQ approaches 1.0 (carbohydrate use); during prolonged low-intensity exercise, it shifts toward 0.7 (fat use). * **Key Enzyme:** Hormone-Sensitive Lipase (HSL) is activated during exercise to promote lipolysis.
Question 17: Which of the following changes is noted during exercise?
- A. Blood flow to the brain increases with an increase in mean systolic blood pressure.
- B. Body temperature increases. (Correct Answer)
- C. Lymphatic flow from muscles decreases.
- D. Blood flow to muscles increases after half a minute.
Explanation: **Explanation:** **Correct Option: B (Body temperature increases)** During exercise, muscle contraction involves the conversion of chemical energy (ATP) into mechanical work. However, this process is only about 20-25% efficient; the remaining 75-80% of energy is released as **metabolic heat**. This leads to a rise in core body temperature, which triggers thermoregulatory mechanisms like cutaneous vasodilation and sweating. **Analysis of Incorrect Options:** * **Option A:** While cardiac output increases significantly, **cerebral blood flow remains constant** (approximately 750 ml/min) due to powerful autoregulation. While systolic blood pressure rises, the brain is protected from these fluctuations to maintain a stable environment. * **Option C:** Lymphatic flow from active muscles **increases** significantly (up to 10-30 fold). This is due to increased capillary hydrostatic pressure (leading to more interstitial fluid) and the "muscle pump" effect, which propels lymph toward the thoracic duct. * **Option D:** Blood flow to muscles increases **immediately** at the onset of exercise (within 1-2 seconds). This is initiated by "command signals" from the CNS and maintained by local metabolic factors (adenosine, $K^+$, $H^+$, and $CO_2$) causing rapid vasodilation. **High-Yield NEET-PG Pearls:** * **The "Active Hyperemia" Effect:** Local metabolites are the primary drivers of increased muscle blood flow during exercise, overriding sympathetic vasoconstriction (Functional Sympatholysis). * **Oxygen Dissociation Curve:** During exercise, the curve shifts to the **Right** (due to increased $H^+$, $CO_2$, Temperature, and 2,3-BPG), facilitating oxygen unloading to tissues. * **Blood Pressure:** Systolic BP increases, but **Diastolic BP** usually remains stable or decreases slightly due to a massive drop in Total Peripheral Resistance (TPR).
Question 18: What physiological changes occur during exercise?
- A. Transient increase in blood flow to muscles immediately after exertion.
- B. Augmentation of cerebral blood flow secondary to elevated systolic blood pressure.
- C. Elevation of core body temperature. (Correct Answer)
- D. Increased oxygen consumption.
Explanation: **Explanation:** **Correct Answer: C. Elevation of core body temperature.** During physical exercise, muscle contraction generates significant metabolic heat as a byproduct of ATP hydrolysis. While the body employs thermoregulatory mechanisms like cutaneous vasodilation and sweating, these cannot fully offset the heat production during intense exertion. Consequently, a controlled rise in core body temperature occurs, which actually shifts the oxyhemoglobin dissociation curve to the right (Bohr effect), facilitating oxygen unloading to active tissues. **Analysis of Incorrect Options:** * **Option A:** This describes **Reactive Hyperemia**. During exercise, blood flow increases *during* exertion (Active Hyperemia) due to local metabolic factors (lactate, adenosine, $K^+$). A transient increase *after* exertion is not the primary physiological hallmark of the exercise state itself. * **Option B:** Cerebral blood flow is remarkably well-maintained through **autoregulation**. Despite significant increases in systolic blood pressure and cardiac output during exercise, cerebral blood flow remains relatively constant to prevent hypertensive brain injury. * **Option D:** While oxygen consumption ($VO_2$) does increase during exercise, in the context of standardized medical examinations, "Elevation of core body temperature" is often cited as the definitive systemic physiological change resulting from the metabolic demand of skeletal muscle. *(Note: In many clinical contexts, D is also true, but C is the classic physiological "change" emphasized in thermoregulation chapters).* **High-Yield NEET-PG Pearls:** * **Cardiac Output:** Increases primarily due to increased Stroke Volume (early) and Heart Rate (late). * **Blood Flow Redistribution:** Shunted from the splanchnic and renal beds to skeletal muscles and the heart. * **Oxyhemoglobin Curve:** Shifts to the **RIGHT** (due to $\uparrow$ Temp, $\uparrow$ $PCO_2$, $\uparrow$ 2,3-DPG, and $\downarrow$ pH). * **Vitals:** Systolic BP increases, while Diastolic BP may decrease or remain stable due to decreased Total Peripheral Resistance (TPR).
Question 19: A manual laborer moves from Kashmir to Delhi in March and works outdoors for a month. Compared with his responses on the first few days in Delhi, for the same activity level after acclimatization, what would one expect?
- A. Higher core temperature
- B. Higher heart rate
- C. Higher sweating rate (Correct Answer)
- D. Higher sweat salt concentration
Explanation: ### Explanation This question tests the physiological mechanisms of **heat acclimatization**. When an individual moves from a cold climate (Kashmir) to a hot climate (Delhi), the body undergoes adaptive changes to improve heat dissipation. **1. Why "Higher sweating rate" is correct:** The primary adaptation to chronic heat exposure is an **increase in the maximum sweat rate** (from ~1.5 L/hr to up to 3 L/hr). The body becomes more efficient at cooling by: * **Lowering the threshold temperature** for the onset of sweating (sweating starts sooner). * **Hypertrophy of sweat glands**, allowing for a greater volume of sweat production to enhance evaporative cooling. **2. Why the other options are incorrect:** * **A. Higher core temperature:** After acclimatization, the body becomes more efficient at dissipating heat. Therefore, for the same workload, the **core temperature is actually lower** compared to the first few days. * **B. Higher heart rate:** Acclimatization leads to an **increase in plasma volume** (by 10–20%). This increases stroke volume, allowing the heart to maintain cardiac output with a **lower heart rate** for the same activity level. * **C. Higher sweat salt concentration:** This is a common distractor. Aldosterone secretion increases during acclimatization, which acts on sweat ducts to **increase reabsorption of Na+ and Cl-**. Thus, the sweat becomes **more dilute (hypotonic)** to conserve electrolytes. **Clinical Pearls for NEET-PG:** * **Plasma Volume:** Increases within the first 3–6 days of heat exposure. * **Aldosterone Role:** Essential for salt conservation in both sweat and urine during heat stress. * **Timeframe:** Full heat acclimatization typically takes **7 to 14 days**. * **Summary of Acclimatization:** ↑ Sweat rate, ↓ Sweat salt, ↓ Threshold for sweating, ↑ Plasma volume, ↓ Heart rate, and ↓ Core temperature.
Question 20: Which of the following is NOT a mechanism that increases blood supply to muscles during exercise?
- A. Local metabolites
- B. Sympathetic stimulation
- C. Cholinergic stimulation
- D. Inhibition of beta receptors (Correct Answer)
Explanation: **Explanation:** During exercise, the body must redistribute cardiac output to active skeletal muscles. This is achieved through a combination of local and systemic mechanisms. **Why "Inhibition of beta receptors" is the correct answer:** Skeletal muscle blood vessels contain **Beta-2 ($\beta_2$) receptors**. When stimulated by circulating epinephrine, these receptors cause **vasodilation**, which increases blood flow. Therefore, **inhibition** (blockade) of beta receptors would cause vasoconstriction or prevent dilation, thereby **decreasing** blood supply to the muscles. This is why the option is the "odd one out." **Analysis of Incorrect Options:** * **Local metabolites (Active Hyperemia):** This is the most potent mechanism for exercise-induced vasodilation. Accumulation of lactate, $CO_2$, $H^+$, Adenosine, and $K^+$ ions causes direct relaxation of precapillary sphincters. * **Sympathetic stimulation:** While sympathetic alpha-1 stimulation causes general vasoconstriction, the overall effect during exercise is a massive increase in cardiac output and "sympatholysis" (where local metabolites override sympathetic constriction in active muscles), ensuring increased flow. * **Cholinergic stimulation:** Skeletal muscles receive **Sympathetic Cholinergic** fibers. These release acetylcholine, which acts on muscarinic receptors to cause vasodilation, specifically during the "anticipatory phase" just before exercise begins. **High-Yield Pearls for NEET-PG:** * **Most important factor** for increased blood flow during exercise: **Local metabolites** (Active Hyperemia). * **Sympathetic Cholinergic System:** Unique to skeletal muscle; responsible for the initial increase in blood flow before metabolic products accumulate. * **Vascular Resistance:** During exercise, Total Peripheral Resistance (TPR) **decreases** due to massive vasodilation in skeletal muscle beds, despite vasoconstriction in the viscera.
Practice by Chapter
Energy Systems in Exercise
Practice Questions
Cardiovascular Responses to Exercise
Practice Questions
Respiratory Adaptations to Exercise
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Muscle Metabolism During Exercise
Practice Questions
Neuromuscular Adaptations to Training
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Exercise in Hot and Cold Environments
Practice Questions
Fatigue Mechanisms
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Recovery Processes
Practice Questions
Training Principles and Adaptations
Practice Questions
Exercise Testing and Prescription
Practice Questions
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