Monitoring the heart and the effect of exerciseSpec B9.2.3, B9.2.4, B9.2.6
In short
Heart activity can be monitored by an ECG, which records the heart's electrical activity, by the pulse rate in beats per minute, or by listening to the valves closing with a stethoscope. Heart rate rises during exercise, so blood delivers more oxygen and glucose to the respiring muscles and removes carbon dioxide faster, then returns to the resting rate.
The activity of the heart may be monitored in three ways.
- An ECG (electrocardiogram), which records the electrical activity of the heart.
- Pulse rate, felt at the wrist or neck, which is the number of beats per minute.
- Listening to the sounds of the valves closing, using a stethoscope.
Investigating the effect of physical activity on heart rate. Independent variable: the activity (for example, minutes of step-ups or jogging on the spot). Dependent variable: heart rate in beats per minute. Control: the same person, same time of day, same length of rest. Repeat and calculate a mean. Safety: stop if you feel dizzy or unwell, and do not take part if you have a heart or breathing condition.
- Sit still for several minutes, then measure the resting pulse rate by counting beats for 15 seconds and multiplying by 4.
- Do a set exercise for a fixed time, for example 2 minutes of step-ups.
- Measure the pulse rate immediately after exercise.
- Keep measuring every minute until the pulse returns to the resting rate. Record the recovery time.
- Repeat with a different level of exercise and compare.
Calculating heart rate from a pulse count
A student counts 19 beats in 15 seconds. Calculate the heart rate in beats per minute.
- 15 seconds is one quarter of a minute
- heart rate = 19 × 4
Answer: 76 beats per minute
Typical results: heart rate rises during exercise and returns to the resting rate during recovery. The harder the exercise, the higher the rate and the longer the recovery.
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanExplaining the effect of exercise
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanDuring physical activity the muscles respire faster, so they need more oxygen and glucose and produce more carbon dioxide. Heart rate increases so that blood flows faster and:
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean- more oxygen and glucose are delivered to the muscles for aerobic respiration
- carbon dioxide is removed more quickly, and lactic acid is carried away from the muscles if anaerobic respiration has happened
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanHeart rate does not rise to 'give the muscles energy'. It rises to deliver oxygen and glucose faster and to remove carbon dioxide.
Written and checked against the Cambridge IGCSE Combined Science (0653) specification · Updated October 2026