Lesson 17 · Lowering the cost of the task
Biomechanics for efficient, sustained movement
Two runners of identical fitness hold the same pace for an hour, and one finishes far more tired than the other. Nothing about their aerobic capacity explains it. What differs is what that pace cost each of them, and cost is something technique decides.
Two runners of identical fitness run side by side at exactly the same pace for an hour. One finishes noticeably more tired than the other. Neither has taken a different route, and neither is carrying an injury.
Write down three things about how they were moving that could account for the difference. Then answer the question this lesson is built on: if you could measure only one thing to find out which of your three explanations is right, what would you measure and why?
- Define efficiency in movement terms, and explain why it decides how long a performance can be sustained.
- Explain how anatomical structures and muscle size and output set the mechanical possibilities for an athlete.
- Explain force absorption and force application, and describe how each can be measured to assess efficiency.
- Apply projectile motion — angle, height and speed of release — to a real skill.
- Explain fluid dynamics, drag and thrust, and how athletes and equipment manage both.
- Explain how a biomechanical change becomes a performance change, rather than describing the change alone.
- Biomechanics — the study of forces and their effects on the human body in movement.
- Efficiency — the ratio of useful work produced to the energy cost of producing it.
- Economy — the energy cost of moving at a given speed, the practical measure of efficiency in endurance sport.
- Force application — the production of force against the ground, water, an implement or an opponent, in a useful direction.
- Force absorption — the dissipation of force on landing or impact, over time and over as much tissue as possible.
- Lever — a rigid segment rotating about a joint; limb length and muscle attachment set its mechanical characteristics.
- Centre of gravity — the point about which a body's mass is balanced.
- Projectile — a body or object in flight, acted on principally by gravity and air resistance.
- Angle of release — the angle to the horizontal at which a projectile leaves the hand, foot or implement.
- Drag — the resistive force opposing motion through air or water.
- Thrust — the propulsive force generated against air or water.
- Streamlining — shaping a body or object to reduce drag.
The dot point asks how biomechanics develops efficient movements for sustained movement, and efficiency is the word to define precisely: the useful work produced relative to the energy it cost. Two athletes moving at the same speed can differ substantially in what that speed costs them, and in a long event the cheaper athlete is the one still moving well at the end.
This is why biomechanics belongs in a training module rather than only in a physics one. In Lesson 8 the way to improve endurance was to raise the ceiling — greater cardiac output, greater maximal oxygen uptake. Biomechanics does the opposite and arguably easier thing: it lowers the cost of the task, so a given pace consumes a smaller fraction of the ceiling the athlete already has.
| Source of waste | What it looks like | Why it costs energy |
|---|---|---|
| Movement in an unhelpful direction | Excessive vertical oscillation in running, side-to-side sway, a wandering swimming line | Muscle work that does not advance the athlete still requires energy, and in running the body must then be lowered and re-accelerated on every stride |
| Unnecessary muscle tension | Gripping hands, hunched shoulders, a clenched jaw | Contracting muscles consume energy whether or not they contribute, and antagonist tension actively opposes the intended movement |
| Poor force direction | Braking forces from over-striding, pushing water sideways rather than backwards | Force applied in the wrong direction must then be overcome, so the athlete pays twice |
| Excess resistance | A high body position in the water, an upright cycling posture, loose clothing | Drag rises steeply with speed, so the extra resistance costs disproportionately more the faster the athlete goes |
And the sustained-movement link, which is the part the dot point actually asks for: an inefficient athlete reaches any given level of fatigue sooner, and as they fatigue their technique degrades further, which raises the cost again. Efficiency does not merely save energy — it protects technique against the fatigue that is coming, which is the same argument Lesson 15 made from the recovery side.
Raising the ceiling is training. Lowering the cost is biomechanics. Both increase how long a pace can be held, and the second is often the faster of the two to change.
Quick check: A runner reduces their vertical oscillation while holding the same pace. The most direct benefit is that:
Anatomical structures set what is mechanically possible. Bones act as levers rotating about joints, and the length of a segment together with where a muscle attaches determines both the force a movement can produce and the speed at which the far end travels. A longer limb moves its end point faster for the same joint rotation, which favours throwing and striking, and costs more to swing, which is a disadvantage in repeated actions. Joint structure sets available range, and the position of the centre of gravity relative to the base of support determines stability.
Muscle size and output then determine what force is available. Larger cross-sectional area allows more force, but only if the athlete can recruit it and direct it usefully — which is the neural adaptation point from Lesson 8. Extra muscle is not free: it must be carried and fuelled, so in a sustained-performance context the useful question is not how much force a muscle can produce but how much useful force per unit of mass carried.
Force then appears in two directions, and the syllabus support material names both.
| Force application | Force absorption | |
|---|---|---|
| What the athlete is doing | Producing force against the ground, water, an implement or an opponent | Receiving force from a landing, a catch, an impact or a collision |
| The principle | Apply force in the direction of intended movement, over the greatest useful range, with the segments sequenced from largest to smallest | Increase the time over which the force is received, and spread it over the largest possible area or the most tissue |
| Done well | A thrower rotating from the ground upwards, so the hand is the last and fastest link in a chain | A landing with flexion at ankle, knee and hip, so the force is absorbed gradually by muscle rather than abruptly by bone and joint |
| Done poorly | An arm-only throw, which discards the force the legs and trunk could have contributed | A stiff-legged landing, which shortens the absorption time so peak force rises sharply |
| Consequence | Less force, or the same force at greater cost | Higher peak forces, which is a direct injury mechanism and links straight to Lessons 20 and 21 |
Notice the last row. Force absorption is the point where this lesson becomes an injury lesson: absorbing the same force over a longer time reduces the peak force the tissue experiences, and peak force is what tissue fails under. That is why landing technique is coached, and why it degrades exactly when fatigue arrives.
True or false: Landing with flexion at the ankle, knee and hip reduces the peak force the tissues experience, because the same impulse (change in momentum) is received over a longer time.
Once an object or body leaves the ground or the hand it is a projectile, and its flight is determined by three things at the moment of release: speed, angle and height. Everything a coach can change about a throw, a jump, a kick or a shot is one of those three.
| Variable | Effect | How much it matters |
|---|---|---|
| Speed of release | The dominant determinant of distance; because both the time in flight and the horizontal velocity increase together, distance rises far faster than speed does | By far the most important of the three, which is why throwing and jumping training is fundamentally about producing more speed at release |
| Angle of release | Sets how the release speed is divided between going up, which buys flight time, and going forward, which uses it | Important, but with a broad optimum. From the same height as landing the optimum is around 45 degrees; when release is above the landing point the optimum falls below 45 |
| Height of release | Greater release height adds flight time for free, so the projectile travels further at the same speed and angle | Modest but real, and largely fixed by the athlete's anatomy and technique rather than freely chosen |
Two applications make this examinable rather than abstract. In the shot put, the shot is released from around shoulder height and lands on the ground, so release is well above landing and the optimum angle is meaningfully below 45 degrees. In basketball shooting, distance is not the goal at all — the target is a hoop of fixed size, so a steeper angle is preferred because it presents a larger effective opening to the ball as it descends.
That second example is the general lesson. The optimum depends on what is being optimised. Maximum distance, maximum accuracy and maximum chance of scoring are three different objectives and give three different answers, and an answer that recites "45 degrees is optimal" without asking what the athlete is trying to achieve has missed the question.
Air resistance complicates all of this
The clean relationships above assume gravity is the only force acting in flight. Real projectiles meet air resistance, which matters more for light objects with a large surface area, such as a shuttlecock or a table tennis ball, and for anything spinning. So treat the three variables as the framework and the air as a real correction to it, rather than assuming the idealised answer is exact.
Fill the gaps. The three release variables of a projectile are speed, height and of release. The resistive force opposing motion through air or water is called . Receiving a landing force over a longer time reduces the experienced by the tissues.
Air and water are both fluids, so an athlete moving through either meets drag, the resistive force opposing motion, and generates thrust, the propulsive force pushing them forward. Net progress is what remains, so a performance can be improved either by increasing thrust or by reducing drag — and for a sustained performance, reducing drag is frequently the better investment because it costs nothing to maintain.
The reason drag matters so much is that it does not rise in proportion to speed; it rises far more steeply, roughly with the square of speed. Doubling speed therefore multiplies drag several-fold. This has two consequences worth stating. Small reductions in drag are worth more at high speed than at low speed, and drag is a much larger share of the total resistance in water than in air, because water is far denser — which is why swimming technique is dominated by drag reduction while running technique is not.
| Sport | Reducing drag | Increasing thrust |
|---|---|---|
| Swimming | A horizontal body position with the hips high, a streamlined push-off, a stable head, minimal lateral movement, and appropriate swimwear | A high-elbow catch that pushes water backwards rather than down, and a full underwater pull |
| Cycling | A lower riding position, close-fitting clothing, equipment shaped for airflow, and riding in the shelter of others | Force applied through the whole pedal stroke rather than only at the top |
| Running | Less important than in the other two, but real at speed and into a headwind, and the reason runners shelter behind others | Force directed backwards and downwards rather than braking ahead of the centre of gravity |
Two of those entries are the same idea in different clothes. Sheltering behind another rider or runner reduces drag without any change to the athlete at all, which is why it is tactically decisive in cycling and in distance running — and it connects this lesson directly to the tactics of Lesson 13, where a decision to refuse to lead into a headwind is a biomechanical decision expressed as a tactic.
Beyond the syllabus · the Magnus effect. A spinning ball travels on a curved path because it drags a thin layer of air around with it: on one side that air moves with the airflow and on the other against it, producing a pressure difference and a sideways force. It is what makes a swinging cricket delivery, a curving free kick and a topspin forehand behave the way they do. This is genuine physics and it is useful for understanding your own sport, but it goes beyond the syllabus's fluid dynamics: drag/thrust. You will still be examined on drag and thrust, on how athletes and equipment reduce drag and increase thrust, and on how that supports sustained performance — no question can require you to explain the Magnus effect by name or by mechanism.
Odd one out. Three of these reduce drag for a swimmer. Which one increases thrust instead?
The syllabus support material specifically mentions the measurement of force absorption and application to assess efficiency, so knowing what can be measured is part of the content. Each measure answers a different question and none answers all of them.
| Measure | What it shows | Limitation |
|---|---|---|
| Video, from a fixed position and angle | Joint angles, body position, timing and sequencing, and change over time | Two dimensions only, so movement towards or away from the camera is distorted; the setup must be identical between sessions to be comparable |
| Force platform | The size, direction and timing of forces applied to the ground, including peak force on landing | Fixed in one place, so it captures a step or a landing rather than a performance |
| Wearable sensors and GPS | Speed, distance, acceleration, ground contact time and cadence, continuously in a real session | Derived quantities depend on the device's own processing, and accuracy varies between products |
| Physiological cost at a fixed speed | The most direct measure of efficiency there is: the same pace costing a lower heart rate or oxygen uptake | It changes with fitness as well as technique, so it cannot separate the two without holding fitness constant |
That last row is what answers card 01. The two runners were matched for fitness, so the difference in how tired they finished is a difference in what the pace cost them — and the single most informative measurement is the physiological cost at a fixed speed, because it measures efficiency itself rather than one of its possible causes. The video then tells you which of your three explanations produced it.
Finally, the dot point's verb is explain, and that requires a chain rather than an observation. A complete answer runs: the biomechanical feature, the mechanical consequence, the effect on energy cost, and then the effect on sustained performance. "She has less vertical oscillation" is an observation. "She has less vertical oscillation, so less work is done lifting the body against gravity on each stride, so the same pace costs less energy, so a greater fraction of her capacity remains available late in the race and her technique degrades later" is an explanation.
Feature, mechanical consequence, energy cost, sustained performance. Four links. Most answers stop after the first, and most marks live in the last two.
Two truths and a lie. One of these statements is false. Find it.
Text description
- Three parts, top to bottom.
- First, three flight paths from the same release speed and height, drawn to scale: 45 degrees travels furthest, while 30 and 60 degrees land at the same point, 60 degrees on a much higher path. A box notes that the optimum follows the goal: in the shot put the release is above landing, so the best angle falls below 45 degrees, and in basketball distance is not the goal, so a steeper angle presents a larger opening at the hoop.
- Then force against time for two landings with equal areas, meaning the same impulse: a stiff landing is a tall, narrow spike, and a flexed landing is a low, wide curve. Peak force is what tissue fails under.
- Last, the four links an explain answer needs: the biomechanical feature, the mechanical consequence, the effect on energy cost, and the effect on sustained performance, the last highlighted.
Activities · from observation to explanation
Each row gives you an observation. Supply the mechanical consequence, the effect on energy cost, and the effect on sustained performance.
A swimmer's hips sit low in the water, so their body is angled rather than horizontal.
A runner's foot lands well ahead of their centre of gravity on each stride.
A cyclist rides upright rather than in a lower position, at 40 km per hour.
A netballer lands from a rebound with very little flexion at the ankle, knee and hip, and does so 40 times a match.
Match each term to its meaning.
- Drag
- Thrust
- Force absorption
- Economy
- The resistive force opposing motion through air or water
- The propulsive force generated against air or water
- Dissipating an impact over time and over as much tissue as possible
- The energy cost of moving at a given speed
Two triathletes are being coached for the same event. Their measured data at a fixed submaximal speed is below.
| Measure | Athlete A | Athlete B |
|---|---|---|
| Heart rate at the fixed running pace, beats per minute | 148 | 171 |
| Vertical oscillation while running, centimetres | 7.5 | 11.8 |
| Ground contact time, milliseconds | 232 | 281 |
| Body position in the water, hip height | high, near horizontal | low, body angled |
| Peak landing force, force platform, multiples of body weight | 4.1 | 6.8 |
| Maximal oxygen uptake, laboratory measure | similar | similar |
Answer five things. Which athlete is more efficient, and which single row is the strongest evidence for that? For athlete B, identify two specific biomechanical causes and run the four-link chain for each. Which measure carries an injury implication rather than an efficiency one, and what would you change? Given that their maximal oxygen uptake is similar, explain why B is nonetheless likely to finish further behind the longer the race is. And finally: name one thing this data cannot tell you, and what you would collect to find it.
Lock it in. In one sentence, explain why improving efficiency can extend how long a pace is held even when nothing about the athlete's aerobic capacity has changed.
Explain how biomechanical analysis can be used to develop more efficient movement and improve performance.
Explain asks how the analysis produces the improvement. Naming biomechanical principles is description; the marks are for what changing a movement achieves.
Plan: name the principle, build linked pairs from analysis to change to outcome, then answer directly.
Efficiency is the ratio of useful work to energy expended. Biomechanical analysis identifies where a movement produces force that does not contribute to the intended outcome, so correcting it either raises performance at the same metabolic cost or sustains the same performance at a lower one.
Analysis of movement patterns identifies motion outside the intended plane — lateral trunk sway in running, or excessive vertical displacement — which requires muscular work while contributing nothing to forward progress, so eliminating it reduces the oxygen cost of a given speed and therefore extends the duration that speed can be sustained.
Analysis of the timing and direction of force application shows whether force is applied in the direction of the intended movement and whether body segments are sequenced from largest to smallest, so correcting the sequence allows momentum to be transferred through the kinetic chain and a greater proportion of the force generated to reach the object or the ground.
Analysis of base of support, centre of gravity and joint alignment identifies positions that are unstable or that load a structure off its axis, so correcting alignment both improves the force the athlete can apply from that position and reduces the repetitive off-axis loading that causes overuse injury — which sustains performance by keeping the athlete available to train.
The analysis is constrained by the athlete: an optimal model movement may be unavailable to a given body because of limb proportions, range of motion or strength, so biomechanics identifies the direction of improvement while the athlete's own structure determines how far it can be taken.
Efficiency is the ratio of useful work to energy expended, and biomechanical analysis identifies where a movement produces force that does not contribute to the intended outcome, so correcting it either raises performance at the same metabolic cost or sustains the same performance at a lower one. Analysis of movement patterns identifies motion outside the intended plane — lateral trunk sway in running, or excessive vertical displacement — which requires muscular work while contributing nothing to forward progress, so eliminating it reduces the oxygen cost of a given speed and extends how long that speed can be sustained. Analysis of the timing and direction of force application shows whether force acts in the direction of intended movement and whether body segments are sequenced from largest to smallest, so correcting the sequence lets momentum transfer through the kinetic chain and a greater proportion of generated force reach the object or the ground. Analysis of base of support, centre of gravity and joint alignment identifies positions that are unstable or load a structure off its axis, so correcting alignment both increases the force applicable from that position and reduces the repetitive off-axis loading causing overuse injury, sustaining performance by keeping the athlete available to train. The analysis is constrained by the athlete, however, since an optimal model movement may be unavailable to a given body because of limb proportions, range of motion or strength — so biomechanics identifies the direction of improvement while the athlete's own structure determines how far it can be taken.
Analyse the relationship between movement efficiency, fatigue and injury risk over the course of a competition.
Analyse asks for the parts and their relationships. Three components are named and the stem adds a time dimension, so the analysis must show how the relationship changes as the contest proceeds.
Plan: identify the components, state the constraint linking them, relate them across the contest, then draw the implication.
Three components interact: movement efficiency, which determines the energy cost of each repetition; fatigue, which accumulates as energy is expended and by-products build; and injury risk, which rises as the athlete's capacity to control loading falls.
They form a loop rather than a chain. Fatigue degrades neuromuscular control, so technique deteriorates and efficiency falls; falling efficiency raises the energy cost of each repetition, which accelerates fatigue; and the degraded technique simultaneously loads structures in positions they are less able to tolerate. Each component therefore worsens the next, and the loop closes.
This is why injuries cluster in the later stages of matches and events. Early in a contest the athlete has the neuromuscular capacity to maintain technique under unexpected load; late in it, the same unexpected load meets a slower, less coordinated response and a movement pattern that has already drifted, so an identical external event produces a very different outcome.
The limiting case isolates the mechanism: two athletes of equal fitness but unequal technical efficiency perform the same work, and the less efficient athlete reaches the point of technical breakdown earlier, so efficiency determines not only performance but the time at which injury risk begins to rise sharply.
It follows that technical training is a form of injury prevention, and that conditioning and technique cannot be treated as separate programs — because the purpose of conditioning is partly to delay the point at which technique fails.
Three components interact: movement efficiency, which determines the energy cost of each repetition; fatigue, which accumulates as energy is expended and by-products build; and injury risk, which rises as the athlete's capacity to control loading falls. They form a loop rather than a chain — fatigue degrades neuromuscular control so technique deteriorates and efficiency falls, falling efficiency raises the energy cost of each repetition and accelerates fatigue, and the degraded technique simultaneously loads structures in positions they are less able to tolerate — so each component worsens the next and the loop closes. This is why injuries cluster in the later stages of matches and events: early in a contest the athlete retains the neuromuscular capacity to maintain technique under unexpected load, whereas late in it the same load meets a slower, less coordinated response and a movement pattern that has already drifted, so an identical external event produces a very different outcome. The limiting case isolates the mechanism — two athletes of equal fitness but unequal technical efficiency performing the same work will differ in when technical breakdown occurs, so efficiency determines not only performance but the point at which injury risk begins to rise sharply. It follows that technical training is itself a form of injury prevention and that conditioning and technique cannot be treated as separate programs, since part of the purpose of conditioning is to delay the point at which technique fails.
Go back to card 01. Two runners at the same pace with the same fitness who finish differently tired differ in efficiency: the same pace cost one of them more. The single most informative measurement is the physiological cost at a fixed speed — heart rate or oxygen uptake at that identical pace — because it measures the thing itself rather than one of its possible causes. Video and force data then identify which cause. If your chosen measurement was a cause rather than the outcome, write down why the order matters: measure the effect first to confirm there is one, then look for its cause.
Multiple choice · 5 questions
MC 1. In a movement context, efficiency is best defined as:
- A. the useful work produced relative to the energy cost of producing it
- B. the maximum force a muscle can generate
- C. the speed at which a skill can be performed
- D. the total distance covered in a session
MC 2. Landing with flexion at the ankle, knee and hip reduces injury risk because it:
- A. reduces the total force acting on the athlete
- B. transfers the force to the upper body
- C. increases the athlete's mass at the moment of contact
- D. increases the time over which the force is received, lowering the peak force the tissues experience
MC 3. Which release variable has the greatest influence on how far a projectile travels?
- A. height of release
- B. angle of release
- C. speed of release
- D. the mass of the projectile
MC 4. A basketball player is coached to shoot with a steeper release angle. The reason is that:
- A. a steeper angle produces greater release speed
- B. distance is not the objective, and a steeper descent presents a larger effective opening at the hoop
- C. 45 degrees is optimal for every projectile skill
- D. a steeper angle reduces air resistance on the ball
MC 5. Why does a small reduction in drag matter more at high speed than at low speed?
- A. because thrust decreases as speed increases
- B. because air becomes denser as an athlete moves faster
- C. because muscles produce less force at high speed
- D. because drag rises far more steeply than speed does, so it is a much larger force to begin with
Short answer · exam style
SA 1. Understand Band 4 Explain the difference between force application and force absorption, giving one example of each and stating the principle that governs it. (4 marks)
SA 2. Apply Band 5 Explain how the angle, height and speed of release affect the flight of a projectile, and explain why the optimal angle of release differs between a shot put and a basketball shot. (6 marks)
SA 3. Evaluate Band 6 Explain how biomechanics can be used to develop efficient movement for sustained performance. Refer to force application or absorption and to fluid dynamics, and explain how each change reaches performance. (7 marks)
📖 Comprehensive answers (click to reveal)
Multiple choice: 1 → A. 2 → D. 3 → C. 4 → B. 5 → D.
Activity 1, indicative answers: 1 → Low hips angle the body, so a larger cross-section is presented to the water and drag rises sharply; more of the swimmer's work goes into overcoming resistance rather than into forward motion, so the same speed costs more energy; the swimmer therefore fatigues earlier, and as they tire the hips drop further, which raises drag again. 2 → Landing ahead of the centre of gravity produces a braking force at contact, so the runner must re-accelerate on every stride and ground contact time lengthens; energy is spent overcoming a force the runner created themselves, so the pace costs more; over an hour this accumulates into significantly earlier fatigue, and the impact is also received abruptly, which raises tissue loading. 3 → An upright position presents a much larger frontal area, and because drag rises far more steeply than speed, at 40 km per hour it is the dominant resistance; the rider must produce considerably more power for the same speed; the higher power costs more energy per kilometre, so the same ride is harder and a fixed effort produces a slower time. 4 → A stiff landing shortens the time over which the impact is received, so peak force rises steeply, and repeating this 40 times a match accumulates loading; the energy cost is a secondary matter here, since the primary consequence is mechanical, with muscle absorbing less and bone, joint and connective tissue absorbing more; the risk of overuse and acute injury rises, and the effect worsens late in the match when fatigue reduces the athlete's ability to control the landing at all.
Activity 2, indicative answers: Athlete A is the more efficient, and the strongest single row is the heart rate at the identical fixed pace, 148 against 171, because it measures the physiological cost of the same task and their maximal oxygen uptake is similar, so the difference cannot be explained by fitness. Two causes for B. Vertical oscillation of 11.8 cm against 7.5: more work is done raising the body against gravity on every stride and it must then be lowered and re-accelerated, so more energy is spent on motion that does not advance the runner, the same pace costs more, and B reaches any given level of fatigue sooner. Low hips in the water: the angled body presents a larger cross-section, drag rises steeply, more of the swimming effort goes into overcoming resistance rather than forward motion, and the same swim speed costs more energy, which compounds across the swim leg and leaves less capacity for the rest of the race. The long ground contact time is a further supporting sign of the same pattern. The measure carrying an injury implication rather than an efficiency one is the peak landing force at 6.8 times body weight against 4.1: the change is to coach landing with greater flexion at ankle, knee and hip so the force is received over a longer time and the peak falls. Why the gap grows with race length: efficiency is a cost per unit of distance, so the penalty accumulates, and because B is working at a higher fraction of a similar capacity they fatigue earlier, and fatigue degrades technique further, which raises the cost again. What the data cannot tell you: whether B's technique holds under fatigue, since every measurement here was taken fresh; the useful additional data is the same measures repeated late in a long session, when technique breakdown is what actually decides a race.
SA 1 (4 marks): Force application [2]: producing force against the ground, water, an implement or an opponent [1], governed by applying force in the direction of intended movement, over the greatest useful range, with segments sequenced from the largest to the smallest so that the final segment is the fastest — for example a thrower rotating from the ground upwards so the hand is the last link, rather than throwing with the arm alone [1]. Force absorption [2]: receiving force from a landing, catch or impact [1], governed by increasing the time over which the force is received and spreading it over as much tissue as possible — for example landing with flexion at ankle, knee and hip so the force is absorbed gradually by muscle rather than abruptly by bone and joint, which lowers the peak force the tissue experiences [1].
SA 2 (6 marks): Speed of release [1]: the dominant determinant of distance, because both the flight time and the horizontal velocity increase with it, so distance rises far faster than release speed does. Angle of release [1]: determines how the release speed is divided between vertical motion, which buys flight time, and horizontal motion, which uses it; from the same height as landing the optimum is around 45 degrees. Height of release [1]: greater release height adds flight time at no cost in speed, so the projectile travels further at the same speed and angle. Shot put [1]: the shot is released from around shoulder height and lands on the ground, so release is well above landing, extra flight time is already available, and the optimum angle is meaningfully below 45 degrees. Basketball [1]: distance is not the objective at all; the target is a hoop of fixed diameter, so a steeper descent presents a larger effective opening for the ball to pass through and is preferred even though it is not the distance-maximising angle. The mark that distinguishes a strong answer [1]: the optimum depends on what is being optimised, so maximum distance, maximum accuracy and maximum chance of scoring give three different answers, and quoting 45 degrees without identifying the objective answers a different question.
SA 3 (7 marks): Efficiency and why it matters [2]: efficiency is the useful work produced relative to the energy it costs, so two athletes at the same speed can differ in what that speed costs them [1]; training raises the ceiling while biomechanics lowers the cost, so a more efficient athlete uses a smaller fraction of their capacity at a given pace, fatigues later, and — critically — because fatigue itself degrades technique, efficiency also protects technique against the fatigue that is coming [1]. A force example with all four links [2]: for instance, a runner who lands ahead of their centre of gravity creates a braking force at each contact [1], so they must re-accelerate on every stride, the pace costs more energy, and over an hour this produces significantly earlier fatigue [1]; equally creditable is a landing example run through to peak force and injury risk. A fluid dynamics example with all four links [2]: for instance, a swimmer holding the hips high lies more horizontal and presents a smaller cross-section [1], so drag falls — and because drag rises far more steeply than speed, this matters more the faster they swim — less work is spent overcoming resistance, the same speed costs less, and more capacity remains for the rest of the event [1]. Measurement [1]: efficiency is measured most directly as the physiological cost at a fixed speed, with video, force platforms and wearable sensors then identifying which biomechanical feature is responsible; a strong answer notes that each measure has limits, for instance that two-dimensional video distorts movement towards or away from the camera and that a fixed-speed physiological measure changes with fitness as well as technique.
This opens the final inquiry question of the focus area, and it reframes everything before it. Lessons 3 to 8 raised the ceiling; this lesson lowers the cost of the task, and both extend how long a performance can be sustained.
Keep two artefacts. The four-link chain — feature, mechanical consequence, energy cost, sustained performance — is what turns an observation into the explanation this dot point asks for. And the force-absorption diagram is the bridge to Lessons 20 and 21, because peak force is what tissue fails under, and it is decided by how the athlete lands rather than by how hard they hit the ground. Lesson 18 turns to recovery strategies.
Mark lesson as complete
Tick when you've finished the practice and review.