2024 IB DP Sports, Exercise and Health Science Practice Paper with Answers

Arterio-venous oxygen difference (\(a\text{-}\bar{v}\text{O}_2\text{ diff}\)) represents the difference in oxygen content between arterial and venous blood. During exercise, active skeletal muscles require and extract more oxygen from the arterial blood to meet the metabolic demands of aerobic respiration. Consequently, the oxygen content of venous blood returning to the heart decreases significantly. Since arterial oxygen content remains relatively constant (due to efficient gas exchange in the lungs), the difference between arterial and venous oxygen content increases.

Award [1] for the correct answer (A). Reject other choices as they do not accurately describe the physiological change in arterio-venous oxygen difference during exercise.

During moderate-to-high intensity exercise, active muscles produce carbon dioxide (\(\text{CO}_2\)) as a byproduct of aerobic metabolism. This increases the partial pressure of carbon dioxide (\(P_{\text{CO}_2}\)) in the blood, leading to an increase in hydrogen ion concentration (which lowers blood pH). Central and peripheral chemoreceptors detect these changes (primarily the rise in \(P_{\text{CO}_2}\) and corresponding drop in pH) and signal the respiratory control center in the medulla oblongata to increase the rate and depth of ventilation.

Award [1] for the correct answer (B). Reject A because blood pH decreases (becomes more acidic) rather than increases. Reject C because arterial oxygen partial pressure does not drop significantly under normal physiological conditions to become the primary stimulus. Reject D because although temperature increases, chemical stimuli are the primary regulator of ventilation.

During muscle contraction, the actin (thin) filaments slide past the myosin (thick) filaments. The A-band, which corresponds to the complete length of the myosin filaments, does not shorten or change length during contraction. The I-band (containing only actin) and the H-zone (containing only myosin in the center of the sarcomere) both shorten, and the overall distance between consecutive Z-discs decreases.

Award [1] for the correct answer (C). Reject A, B, and D because the I-band, H-zone, and distance between consecutive Z-discs all shorten during contraction.

During the downward phase of a pull-up, gravity pulls the body down. To control this descent and prevent a rapid drop, the muscles that performed the upward phase (specifically the latissimus dorsi, which is the primary agonist) must undergo a controlled lengthening while under tension. This is known as an eccentric contraction. Therefore, the latissimus dorsi acts as the agonist, performing an eccentric contraction to slow down the movement.

Award [1] for the correct answer (A). Reject B because a concentric contraction would pull the body upward. Reject C because the biceps brachii also undergoes an eccentric contraction (lengthening under tension) to control the movement, not isometric. Reject D because the pectoralis major is not the primary agonist for this movement.

In a standing calf raise, the foot operates as a second-class lever. In a second-class lever, the load lies between the fulcrum and the effort. Here, the fulcrum is at the metatarsal-phalangeal joints (ball of the foot), the load is the body's weight acting down through the ankle joint, and the effort is applied by the gastrocnemius and soleus muscles pulling upward on the calcaneus via the Achilles tendon. Thus, it is a second-class lever with effort applied by the gastrocnemius.

Award [1] for the correct answer (B). Reject A because it describes a first-class lever and incorrect muscle. Reject C because it describes a third-class lever. Reject D because the floor reaction force is the force acting at the fulcrum, not the muscular effort.

Feedback that comes from an external source (such as a coach) is classified as extrinsic (or augmented) feedback. Feedback that provides detailed information about the patterns of the movement and how the skill was executed (e.g., 'your legs were slightly bent') is known as Knowledge of Performance (KP). In contrast, Knowledge of Results (KR) would focus on the outcome of the performance (e.g., the final score or whether the vault was successful).

Award [1] for the correct answer (B). Reject A and C because the feedback is external, not intrinsic. Reject D because it describes the quality of the movement execution (KP) rather than the outcome (KR).

The complete aerobic breakdown of glucose begins with Glycolysis in the cell cytoplasm (converting glucose into pyruvate), followed by the Krebs cycle in the mitochondrial matrix (which processes acetyl-CoA and produces NADH and FADH2), and ends with the Electron Transport Chain on the inner mitochondrial membrane (which uses these carriers to generate a large amount of ATP through oxidative phosphorylation). Beta-oxidation is only used for fatty acids, not glucose.

Award [1] for the correct answer (B). Reject A because the sequence is incorrect (Krebs cycle occurs after glycolysis). Reject C and D because Beta-oxidation is the pathway for fat breakdown, not glucose.

The Interactionist theory proposed that behavior is a function of both personality traits and situational factors, typically represented by the formula \(B = f(P, E)\), where Behavior (\(B\)) is a function of the stable Personality (\(P\)) and the Environment (\(E\)). Trait theory focuses solely on stable, genetically determined characteristics. Social learning theory suggests behavior is entirely learned from environmental observations and reinforcement.

Award [1] for the correct answer (C). Reject A because trait theory ignores situational influences. Reject B because social learning theory ignores stable internal traits. Reject D because psychoanalytic theory focuses on unconscious drives and conflict.

The immediate increase in heart rate at the very onset of exercise (or even just prior to it) is mediated by the central nervous system (central command) which causes parasympathetic withdrawal (vagal withdrawal) followed closely by an increase in sympathetic nervous system activity. Chemical changes in the blood (like elevated carbon dioxide or lactic acid) take longer to develop and stimulate chemoreceptors, so they do not account for this initial rapid spike.

Award 1 mark for the correct answer (A). No partial marks are awarded for multiple-choice questions.

During a concentric contraction, actin (thin) filaments are pulled toward the center of the sarcomere. This causes the H-zone (the area containing only myosin) to narrow or completely disappear. However, the A-band represents the entire length of the thick myosin filaments, which do not change in length during contraction. Therefore, the H-zone shortens while the A-band remains constant.

Award 1 mark for the correct answer (A).

Carbohydrates are stored in the human body as glycogen. The main reservoirs for glycogen are skeletal muscles and the liver. Glucose is the circulating form in blood, and glucagon is a hormone, not a storage form.

Award 1 mark for the correct answer (B).

The feedback is delivered after the movement has ended (terminal feedback) and focuses on the pattern and quality of the movement execution (Knowledge of Performance) rather than the outcome of the shot (Knowledge of Results).

Award 1 mark for the correct answer (B).

In a second-class lever, the load/resistance lies between the fulcrum and the effort force (Fulcrum - Load - Effort). In a standing calf raise, the ball of the foot (metatarsophalangeal joints) is the fulcrum, the downward force of body weight is the load, and the upward pull of the Achilles tendon is the effort. Thus, it is a second-class lever.

Award 1 mark for the correct answer (B).

The ATP-CP system is only the primary source of ATP for high-intensity efforts lasting up to approximately 10 seconds. For high-intensity efforts lasting between 10 to 90 seconds, such as an 18-second maximal sprint, the lactic acid (anaerobic glycolysis) system becomes the dominant provider of ATP.

Award 1 mark for the correct answer (A).

An action potential initiates at the dendrite or cell body of the motor neuron, travels along the axon, crosses the neuromuscular junction to depolarize the sarcolemma (muscle cell membrane), and propagates down the transverse tubules (T-tubules) to trigger calcium release from the sarcoplasmic reticulum.

Award 1 mark for the correct answer (A).

An individual's actual physical performance characteristics (phenotype) are determined by the interaction of their underlying genetic makeup (genotype) and external environmental factors (such as training intensity, nutrition, and environmental conditions). Genotype is fixed at birth and does not change with training.

Award 1 mark for the correct answer (C).

During sub-maximal steady-state aerobic exercise, an untrained individual's stroke volume increases rapidly and then plateaus (typically around 40% to 60% of \(VO_2\) max). Heart rate also increases and reaches a steady-state plateau to match the metabolic demands of the exercise. Therefore, both stroke volume and heart rate increase and plateau.

Award [1] for the correct answer: A. No partial marks.

The rapid, immediate increase in ventilation at the very start of exercise is driven by neural mechanisms: central command from the motor cortex and feedback from proprioceptors (mechanoreceptors) in the active joints and muscles. Chemical changes (such as changes in arterial \(PCO_2\) or pH) take time to develop and are sensed later by chemoreceptors during the slower secondary rise in ventilation.

Award [1] for the correct answer: B. No partial marks.

During the downward (eccentric) phase of a squat, the quadriceps femoris muscle group is lengthening under tension to control the rate of knee flexion against gravity. This is defined as an eccentric contraction.

Award [1] for the correct answer: C. No partial marks.

The elbow joint is structurally classified as a synovial joint, and functionally/structurally behaves as a hinge joint. Cranial sutures are fibrous joints but are not pivot joints. The hip joint is a ball and socket synovial joint (not cartilaginous). Intervertebral discs are cartilaginous joints (not saddle joints).

Award [1] for the correct answer: A. No partial marks.

A calf raise represents a second-class lever system. The fulcrum (F) is located at the metatarsophalangeal joints (the ball of the foot). The load (L) is the body weight acting downward through the tibia (in the middle). The effort (E) is applied upward by the gastrocnemius and soleus muscles via the Achilles tendon at the heel. Because the load is between the fulcrum and the effort, it is a second-class lever.

Award [1] for the correct answer: B. No partial marks.

Muscle glycogen is broken down into glucose-1-phosphate and converted to glucose-6-phosphate to enter the glycolytic pathway. During high-intensity aerobic exercise, it acts as a rapidly accessible source of glucose for ATP resynthesis, supporting high-rate energy production.

Award [1] for the correct answer: C. No partial marks.

Feedback regarding the execution and technique of a movement (e.g., wrist position during the swing) is classified as Knowledge of Performance (KP). Because this feedback comes from an external source (the coach), it is extrinsic (or augmented) feedback.

Award [1] for the correct answer: B. No partial marks.

The three components of somatotyping are endomorphy (roundness/adiposity), mesomorphy (muscularity), and ectomorphy (linearity/thinness). Elite marathon runners rely on energy efficiency and heat dissipation, which are favored by high linearity and a low body mass-to-surface area ratio, typical of ectomorphy.

Award [1] for the correct answer: C. No partial marks.

In untrained healthy individuals, stroke volume increases progressively during submaximal exercise but plateaus at approximately 40% to 60% of maximum oxygen uptake (\(VO_2\text{ max}\)). Beyond this intensity, any further increase in cardiac output is achieved primarily through an increase in heart rate.

Award 1 mark for the correct option (B). No partial marks.

Tropomyosin is a regulatory protein that wraps around actin filaments. At rest, it covers the myosin-binding sites on actin, preventing the myosin heads from forming cross-bridges. When calcium binds to troponin, troponin shifts tropomyosin out of the way, allowing contraction to occur.

Award 1 mark for identifying the correct regulatory role of tropomyosin (B).

Consuming high-glycemic index carbohydrates immediately post-exercise rapid-starts glycogen resynthesis. Adding protein enhances this effect by stimulating a greater insulin response, which increases glucose uptake into the muscle cells via GLUT-4 transporters.

Award 1 mark for identifying the correct combination of high-glycemic carbohydrates and protein (B).

The autonomous stage of learning is characterized by skills performing automatically without conscious control. The learner can focus on tactical aspects or artistic expression while maintaining high consistency and self-correcting subtle errors.

Award 1 mark for identifying the Autonomous stage (C).

In a third-class lever, the effort force (biceps tendon insertion) lies between the fulcrum (elbow joint) and the load (mass of the forearm and hand). This is the most common lever class in the human musculoskeletal system.

Award 1 mark for selecting the correct example of a third-class lever (B).

Heavyweight powerlifters and weightlifters benefit from high muscularity (mesomorphy) combined with high overall mass and bone density (often associated with endomorphy) to provide leverage and stability, while minimizing ectomorphy (linearity/thinness).

Award 1 mark for the correct option (B).

(a) Strategy B (6% carbohydrate-electrolyte solution) showed the lowest percentage body mass loss (1.1%), indicating it was the most effective protocol at preventing body mass loss.

(b) The standard deviation (SD) for Strategy A (0.3%) is lower than that of Strategy C (0.5%). This demonstrates that the variability of body mass loss was smaller/more consistent among individuals when drinking water (Strategy A) compared to receiving no fluids (Strategy C). However, both protocols still showed greater overall variability than Strategy B (0.2%).

(c) Consuming a carbohydrate-electrolyte solution provides multiple advantages over water alone:
1. Carbohydrate delivery: Maintains blood glucose levels and spares muscle/liver glycogen, postponing the onset of central and peripheral fatigue.
2. Enhanced absorption: Sodium and carbohydrate co-transport in the small intestine accelerates water absorption rates compared to plain water.
3. Fluid retention: Sodium helps maintain extracellular fluid volume and plasma volume, reducing cardiovascular drift and physical strain.
4. Thirst maintenance: Sodium preserves the osmotic drive to drink, ensuring athletes maintain better voluntary hydration habits.

Part (a):
- Award [1] for identifying Strategy B (accept 6% carbohydrate-electrolyte solution).

Part (b):
- Award [1] for stating that Strategy A has lower variability / a smaller standard deviation than Strategy C (0.3% vs 0.5%).
- Award [1] for stating that a lower standard deviation means the participants' responses under Strategy A were more consistent/clustered closer to the mean than under Strategy C.

Part (c):
Award [1] per valid physiological point explained, up to [4 max]:
- Carbohydrate intake spares muscle/liver glycogen levels OR maintains blood glucose levels.
- Sodium/electrolytes promote faster intestinal absorption of water via co-transport mechanisms.
- Electrolytes help maintain plasma/extracellular fluid volume, reducing cardiovascular strain/drift.
- Sodium maintains the osmolality of blood, which sustains the drive to drink/thirst mechanism.
- Carbohydrate utilization prevents hypoglycemia and delays the onset of fatigue.

(a) At 80% MAP, the blood lactate concentration for elite rowers is 3.1 mmol/L.

(b) For both groups, blood lactate concentration increases as exercise intensity (%MAP) increases. However, the accumulation is much more pronounced and occurs at lower relative intensities in recreational rowers (rising from 1.9 to 9.1 mmol/L) compared to elite rowers (rising from 1.1 to 5.4 mmol/L). The onset of blood lactate accumulation (OBLA) is delayed to a higher %MAP in elite rowers.

(c) Several muscular and cardiovascular adaptations explain why elite rowers maintain lower blood lactate concentrations:
1. Increased capillary density around skeletal muscles: Improves local oxygen delivery and facilitates the removal of metabolic byproducts/lactate from active fibers.
2. Increased mitochondrial density and size: Enhances the capacity of the muscle cells to produce ATP aerobically via the Krebs cycle and electron transport chain, reducing reliance on anaerobic glycolysis.
3. Higher activity of oxidative enzymes (e.g., citrate synthase, succinate dehydrogenase): Facilitates rapid aerobic metabolism at higher submaximal workloads.
4. Improved lactate clearance: Greater expression of monocarboxylate transporters (MCT-1 and MCT-4) allows faster shuttling and clearance of lactate to be oxidized in slow-twitch fibers or the heart.
5. Glycogen-sparing effect: Better adaptation for fat oxidation at submaximal levels reduces the rate of pyruvate (and thus lactate) production.

Part (a):
- Award [1] for stating 3.1 mmol/L (accept "3.1").

Part (b):
- Award [1] for stating that blood lactate increases in both groups as exercise intensity increases.
- Award [1] for identifying that recreational rowers experience a steeper/faster rate of lactate accumulation OR that elite rowers maintain lower absolute lactate levels at every exercise stage.

Part (c):
Award [1] per valid physiological adaptation explained, up to [4 max]:
- Increased capillary density improves muscle perfusion / oxygen delivery / lactate removal.
- Greater mitochondrial density/size allows more aerobic ATP resynthesis, decreasing glycolysis reliance.
- Higher concentrations of oxidative enzymes (e.g., succinate dehydrogenase) speed up aerobic pathways.
- Enhanced lactate transport proteins (MCTs) clear lactate from the sarcoplasm more rapidly.
- Improved capacity to oxidize free fatty acids spares glycogen reserves, resulting in less pyruvate/lactate creation.
- High percentage of Type I (slow-twitch) muscle fibers which have high oxidative capacity and lower lactate production rates.

(a) Cardiovascular drift refers to the progressive increase in heart rate accompanied by a parallel decrease in stroke volume during prolonged, steady-state submaximal exercise.

(b) During prolonged exercise in a warm environment, the body core temperature rises. To facilitate thermoregulation, sweat rate increases, causing a loss of body fluids and a subsequent reduction in blood plasma volume. This reduction in plasma volume decreases venous return (the volume of blood returning to the heart). According to Starling's law of the heart, a reduced venous return decreases end-diastolic volume, which directly causes a reduction in stroke volume. Furthermore, vasodilation of cutaneous blood vessels occurs to transport heat to the skin surface, further reducing central blood volume and venous return.

(c) Cardiac output (\(Q\)) is the product of heart rate (HR) and stroke volume (SV) (represented by the formula \(Q = HR \times SV\)). During prolonged steady-state exercise, the body's metabolic demand remains constant, meaning cardiac output must also remain relatively constant. Because stroke volume progressively declines due to fluid loss and cutaneous redistribution, the heart rate must progressively increase to compensate and maintain a stable cardiac output.

Part (a) [2 marks max]
- Award [1] for noting the progressive increase in heart rate.
- Award [1] for noting the corresponding decrease in stroke volume.
- Note: Must mention that this occurs during prolonged, steady-state/submaximal exercise.

Part (b) [4 marks max]
- Award [1] for mentioning increased core temperature leading to increased sweating / fluid loss.
- Award [1] for linking fluid loss to a reduction in blood/plasma volume.
- Award [1] for identifying that reduced plasma volume leads to decreased venous return.
- Award [1] for stating that decreased venous return reduces stroke volume (accept reference to Starling's law/reduced end-diastolic volume).
- Award [1] for stating that cutaneous vasodilation (redirection of blood to the skin for cooling) further reduces central venous return.

Part (c) [2 marks max]
- Award [1] for identifying that cardiac output (\(Q\)) remains relatively constant/stable during steady-state exercise.
- Award [1] for explaining that as stroke volume decreases, heart rate must increase to compensate and maintain this constant cardiac output (must mention the mathematical relationship: \(Q = HR \times SV\)).

(a) Bernoulli's principle states that the pressure exerted by a fluid (such as air) is inversely proportional to its velocity. This means that as the speed of fluid flow increases, the pressure within that fluid decreases, and where the speed of fluid flow decreases, the pressure increases.

(b) When a tennis ball is hit with topspin, it rotates forward (clockwise relative to its forward motion). This rotation drags a layer of air around the ball. On top of the ball, the rotational motion of the ball's surface opposes the oncoming relative airflow, slowing the air down (creating low velocity, which results in high pressure). On the bottom of the ball, the rotational motion travels in the same direction as the oncoming relative airflow, speeding the air up (creating high velocity, which results in low pressure). The resulting pressure differential (high pressure on top and low pressure underneath) generates a downward force (the Magnus force) that pulls the ball down towards the court quicker than gravity alone.

(c) To minimize drag forces, a cyclist can:
1. Adopt an aerodynamic body position (e.g., tucking the head, leaning forward, or using low aerobars to minimize frontal surface area).
2. Use specialized aerodynamic equipment (e.g., streamlined teardrop helmets, deep-section or disc wheels, and aerodynamic frame designs).
3. Wear tight-fitting, specialized skinsuits made of materials designed to reduce surface drag.
4. Ride closely behind another cyclist to benefit from drafting (reducing frontal air resistance).

Part (a) [2 marks max]
- Award [1] for stating that pressure is inversely proportional to velocity in a moving fluid (or equivalent description of velocity-pressure relationship).
- Award [1] for clarifying that high velocity results in low pressure OR low velocity results in high pressure.

Part (b) [4 marks max]
- Award [1] for identifying that topspin causes the ball to rotate in a forward direction.
- Award [1] for explaining that air velocity on top of the ball is reduced due to opposing surface boundary forces, creating high pressure.
- Award [1] for explaining that air velocity below the ball is increased due to surface boundary forces moving in the same direction, creating low pressure.
- Award [1] for concluding that the pressure difference (high pressure above, low pressure below) creates a downward force (Magnus force) causing a steeper downwards trajectory.

Part (c) [2 marks max]
- Award [1] per valid method stated, up to [2 marks max].
- Acceptable answers include:
- Aerodynamic body position / tucking.
- Drafting behind another rider.
- Wearing tight-fitting aerodynamic clothing/skinsuits.
- Using streamlined equipment (e.g., aero helmets, disc wheels, aero frames).

### Part (a) Role of carbohydrates and lipids as energy sources
- At low intensities (e.g., < 50-60% \(VO_2\) max), lipids (fats) are the primary fuel source as they provide a high yield of ATP per molecule through aerobic pathways, though at a slower rate.
- As exercise intensity increases, there is a "crossover point" where the proportion of energy derived from lipids decreases and the proportion from carbohydrates increases.
- During high-intensity exercise (e.g., > 75-80% \(VO_2\) max), carbohydrates become the dominant fuel source because glycogen can be broken down rapidly both aerobically and anaerobically.
- Carbohydrates require less oxygen to produce a given amount of ATP compared to lipids, making them a more efficient fuel source when oxygen delivery is a limiting factor during intense exercise.

### Part (b) Physiological mechanisms of cardiovascular drift
- Cardiovascular drift is a progressive decrease in stroke volume (SV) and a parallel increase in heart rate (HR) during prolonged, steady-state submaximal exercise, while cardiac output (\(Q\)) remains relatively constant.
- In hot environments, the body sweats excessively to facilitate evaporative cooling to regulate core body temperature.
- This prolonged sweating leads to a loss of body fluids, causing a reduction in blood plasma volume.
- Simultaneously, cutaneous vasodilation occurs to direct blood flow to the skin, aiding heat dissipation.
- The combination of reduced plasma volume and venous pooling in the skin vasculature reduces the volume of blood returning to the heart (reduced venous return).
- A reduced venous return decreases end-diastolic volume (EDV) / pre-load.
- According to Starling's Law of the Heart, a lower EDV leads to weaker cardiac contraction and a resulting decrease in stroke volume (SV).
- To maintain a constant cardiac output (since \(Q = \text{HR} \times \text{SV}\)), the heart rate (HR) must progressively increase to compensate for the falling stroke volume.

### Part (c) Nutritional and hydration strategies before, during, and after a marathon

**Before the Marathon (Preparation):**
- **Carbohydrate Loading:** In the 2-3 days leading up to the race, the athlete should consume a high carbohydrate diet (approx. 8-10 g/kg of body weight per day) to maximize muscle and liver glycogen stores.
- **Pre-event Meal:** Consume a meal 3-4 hours prior to the race that is rich in complex carbohydrates, low in fat, fiber, and moderate in protein to top up glycogen reserves while minimizing gastrointestinal distress.
- **Pre-hydration:** Sip fluids (water or sports drinks) in the hours leading up to the race (e.g., 5-7 ml/kg body weight 4 hours prior) to ensure the athlete starts in a euhydrated state.

**During the Marathon (Performance):**
- **Exogenous Carbohydrates:** Consume 30-60 grams (up to 90g if using multiple transportable carbohydrates like glucose-fructose mixtures) of carbohydrates per hour using gels, sports drinks, or chews to maintain blood glucose levels and spare endogenous glycogen.
- **Fluid Replacement:** Drink fluids regularly to match sweat rate, aiming to prevent a body mass loss of greater than 2% while avoiding overhydration (which can lead to hyponatremia).
- **Electrolytes:** Ensure fluids contain sodium and other electrolytes to stimulate thirst, assist with intestinal fluid absorption, and maintain osmotic balance.

**After the Marathon (Recovery):**
- **Rehydration:** Consume fluids equal to approximately 1.5 times (150%) of the body weight lost during the run to fully restore fluid balance.
- **Refueling (Carbohydrates):** Ingest high-glycemic carbohydrates (e.g., 1.0-1.2 g/kg/hour) immediately after exercise and at regular intervals for the first 4 hours to kickstart rapid muscle glycogen resynthesis.
- **Repair (Protein):** Consume 20-25g of high-quality protein shortly after the race to provide essential amino acids to stimulate muscle protein synthesis and repair exercise-induced muscle damage.

### Part (a) [4 marks maximum]
- **[1]** Award 1 mark for stating that lipids are the primary fuel source at low intensities.
- **[1]** Award 1 mark for describing the transition/crossover concept as intensity increases (shift from lipids to carbohydrates).
- **[1]** Award 1 mark for stating that carbohydrates are the dominant fuel source at high intensities.
- **[1]** Award 1 mark for explaining that carbohydrates are more oxygen-efficient (yield more ATP per unit of oxygen consumed than lipids) or are mobilized/metabolized faster.

### Part (b) [7 marks maximum]
- **[1]** Award 1 mark for defining cardiovascular drift (progressive decrease in SV, increase in HR, constant cardiac output \(Q\)).
- **[1]** Award 1 mark for linking hot environments to increased sweating for thermoregulation/evaporative cooling.
- **[1]** Award 1 mark for explaining that sweat loss leads to a reduction in blood/plasma volume.
- **[1]** Award 1 mark for noting cutaneous vasodilation (blood shunted to skin for heat loss).
- **[1]** Award 1 mark for explaining that reduced plasma volume and cutaneous pooling lead to decreased venous return.
- **[1]** Award 1 mark for linking reduced venous return to reduced end-diastolic volume (EDV) / ventricular filling.
- **[1]** Award 1 mark for explaining that reduced EDV decreases myocardial stretch and stroke volume (Starling's Law).
- **[1]** Award 1 mark for linking the reduction in SV to the compensatory increase in HR to maintain constant cardiac output (using the formula \(Q = \text{HR} \times \text{SV}\)).

### Part (c) [9 marks maximum]
*Award maximum 3 marks per phase (Before, During, After).*

**Before (Max 3 marks):**
- **[1]** Carb-loading: High carbohydrate intake (8-10g/kg) 2-3 days prior to maximize glycogen supercompensation.
- **[1]** Pre-event meal: High carb, low fat/fiber/protein 3-4 hours prior to prevent GI distress and top up blood glucose.
- **[1]** Pre-hydration: Drinking fluids (water/electrolyte solutions) hours before to achieve euhydration.

**During (Max 3 marks):**
- **[1]** Exogenous Carbs: Intake of 30-60g (or up to 90g) of carbohydrates per hour to maintain blood glucose.
- **[1]** Fluid Intake: Drinking to match sweat rate / preventing >2% body mass loss.
- **[1]** Electrolytes: Consuming sodium to prevent hyponatremia and assist fluid absorption.

**After (Max 3 marks):**
- **[1]** Rehydration: Ingesting 1.5 times the weight lost to restore fluid balance.
- **[1]** Refueling: Rapid carbohydrate intake (1.0-1.2g/kg/hr) immediately after to optimize glycogen resynthesis.
- **[1]** Repair: Ingesting 20-25g of high-quality protein to support muscle repair and synthesis.