Teacher sheet · Ages 15–16 · about 45–50 minutes
Exercise physiology: heart, muscles and energy
Lesson page: echoesof.science/school/exercise/ages-15-16/ · Pupil worksheet: echoesof.science/school/exercise/ages-15-16/print/
Learning aims
- Use CO = HR × SV with correct units.
- Describe changes in heart rate, stroke volume and cardiac output in exercise; estimate maximum heart rate.
- Compare ATP from creatine phosphate, glycolysis and aerobic respiration; explain lactic acid and oxygen debt.
- Analyse heart-rate recovery data and evaluate measurement uncertainty.
- Interpret population statistics on activity and health critically.
Lesson plan
| Time | Activity |
|---|---|
| 5 min | Starter: why do you keep breathing hard after a sprint? |
| 10 min | Read the text; worked CO example on the board. |
| 20 min | Step test and recovery measurements in pairs. |
| 5 min | Graphs, calculations and uncertainty. |
| 5 min | Quiz, or the Aerobic or anaerobic? game as homework. |
Materials for the experiment
- A stable, low step or gym bench fixed against a wall
- Stopwatch
- Record sheet and graph paper or a spreadsheet
Safety: Use a stable, low step on a non-slip floor. Participation is voluntary; pupils with a health condition follow their care plan or take the role of timekeeper or recorder. Stop at once if anyone feels dizzy, short of breath beyond normal, or has chest pain, and tell the teacher. Data are personal: no comparing or ranking pupils.
Common misconceptions
| Pupils may think… | Actually… |
|---|---|
| Muscles only use aerobic respiration. | At the start of exercise and in intense bursts, creatine phosphate and glycolysis supply ATP without oxygen. |
| Lactic acid is a waste product that is the only cause of fatigue. | Lactic acid may contribute to fatigue; fatigue is when a muscle can no longer contract in response to nerve signals. |
| Cardiac output only rises because the heart beats faster. | Stroke volume rises too, because the heart contracts more strongly. |
Worksheet answers
- Rest: 72 × 0.070 L = 5.04 L/min. After: 144 × 0.110 L = 15.84 L/min. Factor ≈ 3.1.
- Description from class data: a sharp rise, then a fall towards the resting value; recovery time read from the graph.
- Oxygen debt: extra oxygen is needed to make up for the ATP produced without oxygen during exercise, so oxygen intake stays raised until it is repaid.
- ±4 bpm (1 beat × 4). Count for longer (30 s or 60 s) or repeat and take a mean.
Quiz answers
- HR = 80 bpm and SV = 70 mL. What is the cardiac output? 5.6 L/min. 80 × 70 mL = 5,600 mL/min = 5.6 L/min.[6]
- Estimate the maximum heart rate of a 16-year-old. About 204 bpm. 220 − 16 = 204 bpm.[6]
- In exercise CO rises from about 5.25 to 19.5 L/min. By what factor? About 3.7. 19.5 ÷ 5.25 ≈ 3.7, in line with the 4–5 times in the textbook.[6]
- How many times more ATP per glucose does aerobic respiration give than glycolysis alone? About 9 times (36 vs 4). 36 ÷ 4 = 9.[7]
- What is made from pyruvic acid when there is not enough oxygen? Lactic acid. Without oxygen, pyruvic acid is converted to lactic acid.[7]
- Insufficiently active people have a 20–30% higher risk of death. This figure is best described as… an estimate from population studies. Such figures come from studies of large groups and carry uncertainty.[2]
Going further
Design a study to test whether regular training lowers resting heart rate. What would you measure, for how long, and how would you control other variables? Consider the ethics: voluntary participation, privacy and health screening.
Sources used in this lesson
- [1] Physical activity guidelines for children and young people (NHS (UK National Health Service)): reliability High
- [2] Physical activity (fact sheet) (World Health Organization (WHO)): reliability High
- [3] Health Benefits of Physical Activity for Children (Centers for Disease Control and Prevention (CDC)): reliability High
- [6] Anatomy and Physiology, 19.4 Cardiac Physiology (OpenStax, Rice University): reliability High
- [7] Anatomy and Physiology, 10.3 Muscle Fiber Contraction and Relaxation (OpenStax, Rice University): reliability High
Full list with links and a note on each source's reliability: echoesof.science/school/exercise/sources/
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