Energy Systems in Exercise — MCQs
Which of the following is NOT required for gluconeogenesis from lactate?
Least useful for a 800-m run in a competitive event would be
Which of the following tissues relies EXCLUSIVELY on anaerobic glycolysis for ATP production?
Final common pathway of metabolism of carbohydrate, lipids, and protein metabolism is?
Which of the following is active in dephosphorylated state?
During a 100 m sprint which of the following is used by the muscle for meeting energy demands?
A sprinter gets its immediate energy from -
In isometric exercise all are increased except:
Blood supply to the brain during moderate exercise:
During exercise in physiological limits, what is the effect on end systolic volume?
Energy Systems in Exercise Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following is NOT required for gluconeogenesis from lactate?
- A. Transamination of pyruvate to alanine (Correct Answer)
- B. Transport of lactate from muscle to liver
- C. Conversion of lactate to pyruvate
- D. None of the above
Explanation: ***Transamination of pyruvate to alanine*** - While **alanine** can be a substrate for gluconeogenesis, **lactate** is directly converted to pyruvate, which then enters the gluconeogenesis pathway. **Transamination to alanine** is not a required intermediate step for lactate-derived glucose production. - The direct conversion of **lactate to pyruvate** by **lactate dehydrogenase** is the key initial step, not its conversion to alanine. *Transport of lactate from muscle to liver* - **Lactate** produced in muscles (e.g., during intense exercise) must be transported to the **liver** via the bloodstream to be used for **gluconeogenesis** in the **Cori cycle**. - This transport is essential for clearing lactate from the periphery and supplying the liver with a gluconeogenic precursor. *Conversion of lactate to pyruvate* - **Lactate dehydrogenase** catalyzes the reversible conversion of **lactate to pyruvate**, which is the critical first step in converting lactate into a gluconeogenic substrate. - This reaction regenerates **NAD+** (not NADH), which is necessary for glycolysis to continue in muscle tissue. *None of the above* - This option is incorrect because there IS a step listed above that is not required: **transamination of pyruvate to alanine** is indeed not necessary for gluconeogenesis from lactate, making Option A the correct answer to this "NOT required" question.
Question 2: 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 3: Which of the following tissues relies EXCLUSIVELY on anaerobic glycolysis for ATP production?
- A. Skeletal muscle during exercise (anaerobic)
- B. Liver hepatocytes (primarily aerobic)
- C. Cardiac muscle (primarily aerobic)
- D. Mature RBCs (exclusively anaerobic) (Correct Answer)
Explanation: ***Mature RBCs (exclusively anaerobic)*** - **Mature red blood cells** lack mitochondria, making them incapable of **oxidative phosphorylation** and thus relying entirely on **anaerobic glycolysis** for ATP. - This pathway produces **2 net ATP** molecules per glucose molecule, which is sufficient for their metabolic needs like maintaining ion gradients. *Skeletal muscle during exercise (anaerobic)* - While skeletal muscle can perform **anaerobic glycolysis** during intense exercise when oxygen supply is limited, it is not an exclusive reliance. - Skeletal muscle also utilizes **aerobic respiration** and **creatine phosphate** for ATP production depending on activity level and oxygen availability. *Cardiac muscle (primarily aerobic)* - **Cardiac muscle** has a very high metabolic demand and is rich in **mitochondria**, relying almost exclusively on **aerobic respiration** for ATP production. - It uses fatty acids, glucose, and lactate as fuel sources, producing a large amount of ATP efficiently with oxygen. *Liver hepatocytes (primarily aerobic)* - **Liver hepatocytes** are highly metabolically active and primarily rely on **aerobic respiration** for ATP production, performing diverse functions such as gluconeogenesis, glycogenolysis, and detoxification. - Although the liver can perform some anaerobic glycolysis under hypoxic conditions, it is not its exclusive or primary mode of ATP synthesis.
Question 4: Final common pathway of metabolism of carbohydrate, lipids, and protein metabolism is?
- A. Gluconeogenesis
- B. TCA (Correct Answer)
- C. HMP pathway
- D. Glycolysis
Explanation: ***TCA (Tricarboxylic Acid Cycle)*** - The **TCA cycle** (also called Krebs cycle or citric acid cycle) is the **final common oxidative pathway** where all three macronutrients converge - **Carbohydrates** → Pyruvate → **Acetyl-CoA** (via pyruvate dehydrogenase) - **Lipids** → Fatty acids → **Acetyl-CoA** (via beta-oxidation) - **Proteins** → Amino acids → **Acetyl-CoA or TCA intermediates** (via deamination/transamination) - Complete oxidation of acetyl-CoA occurs in the TCA cycle, producing **NADH, FADH2, and GTP** for energy production *Gluconeogenesis* - This is a **biosynthetic pathway** that synthesizes glucose from non-carbohydrate precursors (lactate, glycerol, amino acids) - It is an **anabolic process**, not the catabolic final common pathway for energy production from all macronutrients *Glycolysis* - **Carbohydrate-specific pathway** that converts glucose to pyruvate - It is only the initial breakdown pathway for carbohydrates, not the common pathway where lipids and proteins also converge - Pyruvate from glycolysis must enter TCA cycle for complete oxidation *HMP pathway (Pentose Phosphate Pathway)* - Parallel pathway to glycolysis that generates **NADPH** (for biosynthesis and antioxidant defense) and **ribose-5-phosphate** (for nucleotide synthesis) - Processes only **glucose-6-phosphate** from carbohydrate metabolism - Not involved in lipid or protein metabolism integration
Question 5: Which of the following is active in dephosphorylated state?
- A. PEPCK
- B. Pyruvate Carboxylase
- C. Glycogen Synthase (Correct Answer)
- D. Glycogen Phosphorylase
Explanation: ***Glycogen Synthase*** - **Glycogen synthase** is primarily active in its **dephosphorylated state**, which is promoted by insulin and signals glycogen synthesis. - Dephosphorylation relieves the inhibitory effect of phosphorylation, allowing the enzyme to efficiently add glucose units to a **growing glycogen chain**. *PEPCK* - **Phosphoenolpyruvate carboxykinase (PEPCK)** activity is primarily regulated at the transcriptional level, not typically by phosphorylation state for activation. - Its expression is induced by **glucagon** and **cortisol** during gluconeogenesis. *Pyruvate Carboxylase* - **Pyruvate carboxylase** is allosterically activated by **acetyl-CoA** and its activity is not directly regulated by phosphorylation/dephosphorylation in the same manner as glycogen synthase. - This enzyme plays a key role in **gluconeogenesis** by converting pyruvate to oxaloacetate. *Glycogen Phosphorylase* - **Glycogen phosphorylase** is active in its **phosphorylated state**, particularly the 'a' form, which is promoted by glucagon and adrenaline for glycogen breakdown. - Phosphorylation activates the enzyme, leading to the **breakdown of glycogen** into glucose-1-phosphate.
Question 6: During a 100 m sprint which of the following is used by the muscle for meeting energy demands?
- A. Phosphofructokinase
- B. Phosphocreatine (Correct Answer)
- C. Glucose 1 - phosphate
- D. Creatine phosphokinase
Explanation: ***Phosphocreatine*** - **Phosphocreatine (PCr)** is the primary energy source for a **100m sprint** (lasting 10-20 seconds). - The **ATP-PC (phosphagen) system** provides **immediate energy** by rapidly regenerating **ATP** from ADP through the transfer of a high-energy phosphate group. - This system is crucial for **short bursts of maximal intensity exercise** where energy demand exceeds the capacity of glycolysis and oxidative phosphorylation to respond quickly enough. - Phosphocreatine stores can fuel maximum effort for approximately **10-15 seconds**, making it ideal for sprint activities. *Phosphofructokinase* - **Phosphofructokinase (PFK)** is a key regulatory enzyme in **glycolysis**, not an energy substrate. - While PFK-catalyzed glycolysis contributes ATP during intense exercise, it cannot provide energy as rapidly as the phosphocreatine system. - Glycolysis becomes more prominent after the first 10-15 seconds of maximal effort. *Glucose 1-phosphate* - **Glucose 1-phosphate** is an intermediate in **glycogenolysis** (breakdown of glycogen to glucose-6-phosphate). - It is part of the pathway leading to glucose availability for glycolysis, but is not a **direct, immediate energy source** for muscle contraction. - Unlike phosphocreatine, it cannot directly regenerate ATP. *Creatine phosphokinase* - **Creatine phosphokinase (CPK)**, also known as **creatine kinase (CK)**, is the **enzyme** that catalyzes the reversible transfer of phosphate from phosphocreatine to ADP. - It facilitates the energy transfer reaction but is **not an energy substrate** itself. - The enzyme enables the phosphocreatine system to function, but the actual energy comes from phosphocreatine.
Question 7: A sprinter gets its immediate energy from -
- A. Fatty acid
- B. Creatine phosphate (Correct Answer)
- C. Glycogen
- D. None of the options
Explanation: ***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.
Question 8: In isometric exercise all are increased except:
- A. Mean arterial pressure
- B. Systemic vascular resistance (Correct Answer)
- C. Cardiac output
- D. Heart rate
Explanation: ***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
Question 9: 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 10: During exercise in physiological limits, what is the effect on end systolic volume?
- A. ESV decreases (Correct Answer)
- B. ESV increases
- C. ESV first decreases and then increases
- D. ESV remains unchanged
Explanation: ***ESV decreases*** - During exercise, **sympathetic nervous system activity** increases, leading to enhanced cardiac contractility. - Improved contractility allows the heart to eject a greater percentage of its end-diastolic volume, resulting in a smaller **residual volume** in the ventricle after systole. *ESV increase* - An increase in ESV would indicate a **reduced ejection fraction** and poorer cardiac efficiency, which is contrary to the physiological adaptations during exercise. - This typically occurs in conditions of **heart failure** or myocardial dysfunction, not healthy exercise. *ESV first decrease and then increases* - While there are complex physiological responses during exercise, the primary and sustained effect on ESV within physiological limits is a **net decrease** due to increased contractility. - A subsequent increase would suggest a decline in cardiac function or the onset of fatigue beyond physiological limits. *ESV remain unchanged* - An unchanged ESV would imply no significant alteration in **cardiac contractility** or **ejection efficiency**, which is inconsistent with the cardiovascular demands and adaptations during exercise. - The body actively works to optimize cardiac output by increasing stroke volume, partly by reducing ESV during exercise.
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