Science 7–10 · Year 9

Pulse and breathing rate before and after exercise: body systems responding together

Science understanding: Biological sciences

PracticalLow risk

The idea

When muscles work harder, the nervous system raises heart rate and breathing rate together, so the circulatory and respiratory systems deliver more oxygen and carry away the extra carbon dioxide the muscles produce; when exercise stops, both rates fall back toward resting over several minutes.

Safety card

Low riskAn adult supervises

Hazards

Over-exertion
Asthma, heart or other medical conditions made worse by exercise
Tripping or falling from the step
Embarrassment about fitness in front of peers

Controls

The teacher checks health care plans before the lesson; anyone with a condition, an injury or who prefers not to exercise takes the timing and recording role
Moderate pace only; stop at once if dizzy, short of breath or in pain, and tell the teacher
Step on a flat, non-slip floor against a wall
Class results pooled without names

Note

No hazardous chemicals; record a RiskAssess risk assessment for the activity as school procedure requires.

What you need

A stopwatch or timer that shows seconds, one per pair
A sturdy step or the bottom stair of a staircase, or open floor space for marching on the spot
A results table with columns for resting readings and for readings at 0, 1, 2, 3, 4, 5, 6, 7 and 8 minutes after exercise
Optional: a finger-clip heart-rate monitor or pulse oximeter to check the hand counts

How to do it

Sit quietly for three minutes. Find the pulse on the thumb side of the wrist (or beside the windpipe in the neck), count the beats for 30 seconds and double the count, the method healthdirect describes. Take three resting readings and calculate the mean.
While the subject is still resting, the partner counts breaths (chest rises) for 30 seconds and doubles the count.
Exercise for two minutes at a steady pace the subject can keep up while still able to speak: step up and down the step, or march on the spot lifting the knees.
Sit down immediately. Count the pulse for 15 seconds and multiply by 4 (a shorter count because the rate is changing quickly), then count breaths for the next 15 seconds and multiply by 4. Repeat both counts at the start of every minute for eight minutes.
Stop recording once the pulse is within 5 beats per minute of the resting mean on two readings in a row, and record that time as the recovery time.
Plot pulse rate and breathing rate against time with the resting mean drawn as a horizontal line. Pool recovery times as a class, without names.
Draw a flow diagram of the response linking the nervous, circulatory and respiratory systems, from the stimulus (exercise) to the effectors (heart and breathing muscles) and the response, using the curve as the evidence of how fast each rate rose and recovered.

What you should see

Resting pulse for most learners falls in or near the 60 to 100 beats per minute that healthdirect gives as normal for adults; the three resting counts agree within a few beats per minute. The first count after exercise is the highest. The pulse then falls back toward the resting line, fastest at first; record whether it reaches the line within the eight minutes. Breathing rate follows the same shape. The recovery time is the learner's own measured value, and the class spread shows variation between people. The learner knows it worked when the curve rises above the resting line and returns toward it.

What changes

What you change: Time since exercise stopped (min)
What you measure: Pulse rate (beats per minute) and breathing rate (breaths per minute)
What you keep the same: Exercise type, pace and duration
Step height
Sitting posture for every reading
Counting method and counting time
Same person counting for one subject

Common misconceptions

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

The heart beats faster during exercise to make more oxygen; it pumps faster to deliver oxygen and remove carbon dioxide.
Heart rate falls after exercise because the heart is tired; it falls because the stimulus has gone and the nervous system slows it.
The rates drop back to resting the moment exercise stops; they fall over several minutes, fastest at first.

Curriculum references

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

Science 7–10 Syllabus (2023)SC5-DIS-01 SC5-WS-04 SC5-WS-05 SC5-WS-06
Australian Curriculum v9AC9S9U01AC9S9I03AC9S9I04AC9S9I05

Sources

The pages the author read to write this activity.

All Concept Studio activities