Biology 11–12 · Year 12

Heart rate, breathing rate and oxygen saturation before, during and after exercise

Module 8: Non-infectious Disease and Disorders (Homeostasis)

PracticalLow risk

The idea

Exercise disturbs the body's internal environment and heart and breathing rates rise to correct it, then fall back toward resting values, while blood oxygen saturation stays nearly constant: a negative feedback response the learner can measure on themselves.

Safety card

Low riskAn adult supervises

Hazards

Falls from the step
Participants with heart, respiratory or other health conditions
Competitive over-exertion

Controls

Stable step, suitable footwear, handrail on stairs
Check health status in advance; the source directs that learners with an identified physical or health condition are not involved and take a recording role instead, and that asthmatics may be able to take part if they use their inhaler before starting, which is a decision for the learner, their parent and their doctor, never a direction from the school
Keep the activity non-competitive and stop anyone who feels unwell

Note

Learners are participants: participation is voluntary, anyone may opt out or withdraw their data, and results are recorded without names, following the briefing and consent approach in the practicalbiology.org human-subject protocols.

What you need

Stop clock or phone timer; a stable step or low bench 20 to 30 cm high, or a staircase with a handrail
Pulse oximeter (optional), cleaned between users
Metronome app to set one stepping rate for every participant
Briefing and consent sheet; individual results table; class spreadsheet

How to do it

Sit quietly for 5 minutes, then count your radial pulse for 30 seconds and double it; repeat three times and take the mean as resting heart rate. Record resting breathing rate over 1 minute and, if available, oxygen saturation.
Plot the class's resting heart rates as a histogram in 5 beat per minute bands and note the spread; compare it with the spread of resting oxygen saturation.
Record heart rate once more after being told you are about to exercise.
Step up and down at the metronome rate for 2 minutes; take heart rate, breathing rate and saturation immediately afterwards.
Record heart rate every minute until it is within 5 beats per minute of your resting mean; the time taken is your recovery time.
Volunteers repeat for 1 and 3 minutes of exercise; plot heart rate against time after exercise and recovery time against exercise duration, and draw the negative feedback loop that returns heart rate toward resting.

What you should see

Heart and breathing rates rise with exercise and fall back over the following minutes, and longer exercise gives a higher peak and a longer recovery; anticipating exercise alone raises heart rate by a few beats per minute, as the source notes. Oxygen saturation varies far less than heart rate between people and changes little with exercise. A rise from 72 to 126 beats per minute is a 75 percent increase (computed). The learner knows it worked when every participant's heart rate returns to within 5 beats per minute of resting and recovery time lengthens with exercise duration.

What changes

What you change: exercise duration (1, 2 or 3 minutes)
What you measure: peak heart rate, breathing rate and recovery time
What you keep the same: stepping rate and step height
posture while measuring
counting method
time since last meal or caffeine

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Homeostasis keeps every variable fixed; heart rate changes widely so that blood gases and temperature stay near their set range.
A higher resting heart rate is always unhealthy; resting rate varies between healthy people and with fitness.
Negative feedback means a harmful effect; it means a response that reverses the change that triggered it.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Biology Stage 6 Syllabus (2017), current: Year 11 taught to the end of 2026 and Year 12 to Term 3 2027BIO12-15 BIO11/12-5
Biology 11–12 Syllabus (2025), Year 11 focus area Cells to systems; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-11-02
Biology 11–12 Syllabus (2025), Year 11 Working scientifically; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-11WS-03 BI-11WS-04 BI-11WS-05
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

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